ULTIMATE ANGLING - the Ultimate SA Fishing website
General Angling Topics => Conservation and Ethics => Topic started by: John F on April 02, 2013, 08:57:32 AM
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Starting this thread to share some interesting and relevant published research on fish and fisheries....
Enjoy!
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Response to ocean acidification in larvae of a large tropical marine fish, Rachycentron canadum
* Currently, ocean acidification is occurring at a faster rate than at any time in the last 300 million years, posing an ecological challenge to marine organisms globally;
* There is a critical need to understand the effects of acidification on the vulnerable larval stages of marine fishes, as there is potential for large ecological and economic impacts on fish populations and the human economies that rely on them;
* Larval cobia were raised through the first 3 weeks of ontogeny under conditions of predicted future ocean acidification to determine effects on somatic growth, development, otolith formation, swimming ability, and swimming activity;
* Cobia exhibited resistance to treatment effects on growth, development, swimming ability, and swimming activity;
* However, these scenarios resulted in a significant increase in otolith size (up to 25% larger area) at the lowest pCO2
levels reported to date, as well as the first report of significantly wider daily otolith growth increments.
* When raised under more extreme scenarios of 3500 and 5400, cobia exhibited significantly reduced size-at-age (up to 25% smaller) and a 2–3 days developmental delay;
* The robust nature of cobia may be due to the naturally variable environmental condi tions this species currently encounters throughout ontogeny in coastal environments, which may lead to an increased acclimatization ability even during long-term exposure to stressors.
Those interested in reading the full paper please let me know.
Reference:
Bignami, S., S. Sponaugle & R. K. Cowen (2013). Response to ocean acidification in larvae of a large tropical marine fish, Rachycentroncanadum. Global Change Biology, 19: 996-1006.
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Nice thread, hope to add something useful here soon!
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Thanks Marcos. Is it known why ocean acidification is accelerating?
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Yes, increase of CO2 in the atmosphere, which dissolves in the water and form carbonic acid. This is an emergent line of research as it has huge implications for tropical countries. As you know coral reefs are basically calcium carbonate deposits. Ocean acidification basically means all carbonate will be dissolved. No more coral reefs. The socio-economic consequences are simply catastrophic!
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That is damn scary!
"We civilse left, we civilse right....."
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Genetic divergence between populations of Lichia amia
* Lichia amia is an important coastal recreational fishery species with a cosmopolitan distribution in the eastern
Atlantic. In southern Africa, it is distributed from southern Angola to northern KwaZulu-Natal in South Africa.
* A recent biological survey revealed differences between Angolan and South African individuals suggesting that they
may represent separate stocks.
* As fishery management decisions should be based on accurate knowledge of population structure, an initial survey of the genetic substructuring of L. amia was conducted on samples collected in southern Angola and South Africa.
* Two deeply divergent (southern Angolan and South African) populations were identified across the Benguela Current system.
* The results suggest that Angolan and South African L. amia should be managed as two independent stocks.
PDF available. Those interested please send me a PM.
Reference
Henriques, R., W. M. Potts, W. H. H Sauer & P. W. Shaw (2012). Evidence of deep genetic divergence between populations of an important recreational fishery species, Lichia amia L. 1758, around southern Africa. African Journal of Aquatic Science, 34: 585-591.
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Ingestion of plastic marine debris by longnose lancetfish (Alepisaurus ferox) in the North Pacific Ocean
* Plastic marine debris affects species on most trophic levels, including pelagic fish;
* While plastic debris ingestion has been investigated in planktivorous fish in the North Pacific Ocean, little knowledge exists
on piscivorous fish;
* The objectives of this study were to determine the frequency of occurrence and the composition of ingested plastic marine debris in longnose lancetfish (Alepisaurus ferox), a piscivorous fish species captured in the Hawaii-based pelagic longline fishery.
* Nearly a quarter (47 of 192) of A. ferox sampled contained plastic marine debris, primarily in the form of plastic fragments (51.9%);
* Further research is needed to determine residence time of ingested plastic marine debris and behavior of toxins associated with plastic debris.
Reference
Jantz, L. A., C. L. Morishige, G. L. Bruland & C. A. Lepczyk (2013). Ingestion of plastic marine debris by longnose lancetfish (Alepisaurus ferox) in the North Pacific Ocean. Marine Pollution Bulletin, 69: 97-104.
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Thanks for this thread Marcos.
A question on the Garrick. I was under the impression that the 2 were acknowledged as separate species, the Angolan and upwards being "Tropical Garrick" as opposed to our "Southern Garrick".
Also, what is pCO2?
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Thanks for this thread Marcos.
A question on the Garrick. I was under the impression that the 2 were acknowledged as separate species, the Angolan and upwards being "Tropical Garrick" as opposed to our "Southern Garrick".
Also, what is pCO2?
So far their are recognized as a single species, although it seems they are following a speciation path into separate species.
pCO2 is the partial pressure of CO2. In the atmosphere, the partial pressure of CO2 is defined as the pressure the CO2 would exert if all other gases were removed. The sum of the partial pressure of all the atmospheric gases will equal the atmospheric pressure.
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Thanks, I had never heard the term before. Seems one is never too old to learn new stuff.
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Contribution of a large no-take zone [Pondoland MPA] to the management of vulnerable reef fishes in the South-West Indian Ocean
* This study, based in the South-West Indian Ocean, evaluated the benefits of area closure to vulnerable fishery species, which have been depleted by overfishing.
* A controlled fishing survey was conducted seasonally between 2006 and 2011 in the Pondoland MPA on the East Coast of South Africa. The MPA includes a 400 km2 no-take zone where all forms of vessel-based exploitation are prohibited.
* Three endemic sparids (slinger Chrysoblephus puniceus, Scotsman Polysteganus praeorbitalis and poenskop Cymatoceps nasutus) and one widely distributed serranid (yellowbelly rockcod Epinephelus marginatus) were chosen as study species.
* These are slow growing, high trophic level species, which are prominent on rocky reefs in the Pondoland area and have been depleted by overfishing. Relative abundance was estimated using catch-per-unit-effort (CPUE) and length frequency
distributions were used to determine the size structure of fish populations.
* The relative abundance and the mean length of all four species were significantly greater in the no-take zone.
* Over the 5-year study period, CPUE of C. puniceus and C. nasutus in the no-take zone increased as did the mean length of all
species, except C. nasutus.
* This study presents clear evidence that the Pondoland MPA no-take zone is providing insurance against the depletion of vulnerable fishery stocks in fished areas, thereby establishing the basis for the enhancement of adjacent fisheries.
PDF available. Those interested please send me a PM.
Reference
Maggs, J. Q., B. Q. Mann & P.D. Cowley (2013). Contribution of a large no-take zone to the management of vulnerable reef fishes in the South-West Indian Ocean. Fisheries Research, 144: 38-47.
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Amazing how important these MPA's are proving to be! Keep these posts coming Marcos... very interesting!
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100% correct Reefman. That's why i'm against beachdriving being allowed again... it has created natural MPA's especially in the southern cape for inshore reef species in particular....
Anycase very interesting information.....
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Thanks John F! Very informative and great reading.
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:+ cred: Something to really monitor! Would you mind mailing me the whole paper?
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:+ cred: Something to really monitor! Would you mind mailing me the whole paper?
:corrct: email sent.
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Thank you, what can the average Joe do about this? I have red about people doing strange things to try and counter this, from dumping metal phosphate into the water to try and change the PH... We know we must reduce carbon, but how do we fix the problem? Assume the person with the answer will be a billionaire soon....
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Like everything else, it's not what ONE individual can do, but the cumulative efforts of millions of ONE's.... this is what, in my opinion, humans still have to realize... gotta learn from bees and ants...
Environmental degradation is rarely caused by the actions of one individual (well, except oil spills and similar)... as a society we need to waste less, recycle/re-use/reduce more. Have less babies and stop thinking about today... every single planning exercise is done on a 4/5 year basis... nature does not operate like that!
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Awesome info there Marcos!
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Like everything else, it's not what ONE individual can do, but the cumulative efforts of millions of ONE's.... this is what, in my opinion, humans still have to realize... gotta learn from bees and ants...
Environmental degradation is rarely caused by the actions of one individual (well, except oil spills and similar)... as a society we need to waste less, recycle/re-use/reduce more. Have less babies and stop thinking about today... every single planning exercise is done on a 4/5 year basis... nature does not operate like that!
Brilliantly put! :+ cred:
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John I really enjoyed these posts on the research about the Lichia amia.
I assume that they are classified as sub species, but is it still possible for the populations to interbreed?
And is it known if individuals travel between the two areas?
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At this stage they're still considered as part of the same species (despite biological and genetic differences). Just separate stocks or sub-populations diverging slowly... eventually they will evolve into 2 whole different species.
The genetics study mentioned above, found a highly genetic divergence and isolation between the two stocks which means they don't interbreed mainly due to physical barriers - the authors cite the oceanographic features of the Benguela current (doesn't necessarily mean they can't! I supposed if you put them together in a tank they would?).
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It's quite an interesting species actually... was reading a bit more about it....
A study done in 2008 (Smith, 2008) concluded that the (then) current stock was only at 14% of its unfished level!!!
This study also analyzed tagging data from the ORI database. of the 6456 fish tagged only 457 had been recaptured (7%)!
Only 16% (71) of the re-captured fish were re-released!
These fish migrate along the KZN-Cape-KZN coast but not a single fish tagged in the Cape area has been reported in Angola (no surprises there! :hehe:).
Reference (PDF available)
Smith, D. (2008). Movement, growth and stock assessment of the coastal fish Lichia amia (Teleostei: Carangidae) off the South African coast. MSc thesis, 164 pp. Durban, University of KwaZulu-Natal, School of Life & Environmental Sciences.
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thank you :udman:
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How many legs does an octopus have?
Extract from the book " The Second Book Of General Ignorance" by John Lloyd and John Mitchenson
Two.
Octopuses have eight limbs protruding from their bodies, but recent research into how they use them has redefined what they should be called. They use their back two tentacles to propel themselves along the seabed, leaving the remaining six to be used for feeding. As a result, marine biologists now tend to refer to them as animals with two legs and six arms.
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How many legs does an octopus have?
Extract from the book " The Second Book Of General Ignorance" by John Lloyd and John Mitchenson
Two.
Octopuses have eight limbs protruding from their bodies, but recent research into how they use them has redefined what they should be called. They use their back two tentacles to propel themselves along the seabed, leaving the remaining six to be used for feeding. As a result, marine biologists now tend to refer to them as animals with two legs and six arms.
It's such an awesome book. It was based on the BBC TV program QI also by John Loyd but with Stephen Fry as host. It's a good and interesting laugh.
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Surveys of white sharks (Carcharodon carcharias) off bathing beaches in Algoa Bay, South Africa
* The study provides information on the existence of a possible inshore nursery area for white sharks (Carcharodon carcharias) in Algoa Bay, South Africa.
* In total, 43 flights were conducted, using a Robinson R22 helicopter, between October 2010 and March 2012.
* A total of 50 white sharks was sighted, with a maximum sighting rate of seven sharks per hour in October 2010.
* The majority (96.0%) of sharks observed were less than 2.5m in length, immature and sighted between October and March (98.0%).
* Modelling showed that water temperature and barometric pressure explained the sightings of sharks, peaking in mid-December.
* A total of 58 white shark catches was recorded from key informant interviews with shore anglers between July 2009 and December 2011.
* Sharks ranged in size from 1.5 to 2.5m in total length, with young-of-the-year sharks (,1.75 m) accounting for 69.0% of the catch.
* Defining key habitats for young-of-the-year and juveniles is critical for the management and conservation of white sharks worldwide.
PDF available. Those interested please send me a PM.
Reference
Dicken, M. L. & A. J. Booth (2013). Surveys of white sharks (Carcharodon carcharias) off bathing beaches in Algoa Bay, South Africa. Marine and Freshwater Research, 64: 530-539.
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Just shows you the importance of the ban on GW fishing in SA, there are many of them but not of breeding age.
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Which also means they are only now after 20 years starting to effectively breed as well!
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A review of the Oceanographic Research Institute’s Cooperative Fish Tagging Project: 27 years down the line
* The Oceanographic Research Institute’s (ORI) Cooperative Fish Tagging Project was initiated in 1984 and is one of the most enduring and successful environmental projects of its kind in South Africa.
* By the end of 2011, 5 130 anglers had joined the project, of whom 3 457 had tagged one or more fish.
* In the project’s 27-year history (1984–2011), over 251 900 fish from 368 different species have been tagged and released, of which approximately 13 192 (5.2%) have been recaptured.
* The five most commonly tagged species to date are galjoen, dusky kob, dusky shark, garrick/leervis and spotted
grunter.
* Information from the Tagging Project has been extensively used in numerous research projects, scientific publications, popular articles and postgraduate theses.
* The results generated by this project have also contributed to policy development and decision-making on linefish management in South Africa.
* Furthermore, the project has had a positive impact on improving angler awareness and knowledge about linefish resources. The concept of tag and release has partly been responsible for changing the ethics of the recreational fishing community, many of whom now release their catch, thereby contributing to a more sustainable fishing future.
PDF available. Those interested please let me know.
Reference:
Dunlop, S. W., B. Q. Mann & R. P. van der Elst (2013). A review of the Oceanographic Research Institute’s Cooperative Fish Tagging Project: 27 years down the line. African Journal of Marine Science, 35(2): 209-221.
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The effects of barotrauma on five species of South African line-caught fish
* Management measures for South African line-caught fish include output controls such as closed seasons, bag
and size limits and no-take moratoria.
* The main condition for these measures to be effective is that undesirable catches can be successfully released.
* However, most of the line-caught fish species are susceptible to barotrauma, a condition caused in physoclists [fishes with closed swimbladders] by the rapid reduction of hydrostatic pressure during the ascent to the surface
during capture.
* The effects of barotrauma on five commercially important species were investigated: roman, silver kob, hottentot, santer and carpenter.
* A classification of the external signs of barotrauma was developed and internal and external signs of barotrauma were examined in relation to fishing depth and fish size, and compared between species.
* Immediate post-release mortality was investigated during a catch-and-release experiment.
* Medium-term survival of roman (~1 d) was examined by returning fish to depth in cages and subsequent monitoring on SCUBA.
* Results indicate that most of the fish experience barotrauma even when caught at relatively shallow depths.
* External signs include extension of the inflated, everted stomach through the mouth, distended eyes, protrusion of the hind-gut and other organs through the cloaca, and gas bubbles in the dermal tissue between the fin rays.
* The absence of any obvious external signs of barotrauma can be misleading as dissections of such fish revealed ruptures of the swimbladder and other internal injuries consistent with barotrauma.
* Results indicate that there might be significant post-release mortality, a factor that needs to be taken into account during stock assessment predictions and during the implementation of catch restrictions.
PDF available. Those interested please let me know.
Reference:
Kerwath, S. E., C. G. Wilke & A. Götz (2013). The effects of barotrauma on five species of South African line-caught fish. African Journal of Marine Science, 35(2): 243-252.
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Can fish really feel pain?
* The paper reviews studies claiming that fish feel pain;
* Deficiencies in the methods used for pain identification were found, particularly for distinguishing unconscious detection of injurious stimuli (nociception) from conscious pain;
* Results were also frequently misinterpreted and not replicable, so claims that fish feel pain remain unsubstantiated;
* Comparable problems exist in studies of invertebrates;
* In contrast, an extensive literature involving surgeries with fishes shows normal feeding and activity immediately or soon after surgery.
* C fiber nociceptors, the most prevalent type in mammals and responsible for excruciating pain in humans, are rare in teleosts and absent in elasmobranchs studied to date;
* A-delta nociceptors, not yet found in elasmobranchs, but relatively common in teleosts, likely serve rapid, less noxious injury signaling, triggering escape and avoidance responses;
* Clearly, fishes have survived well without the full range of nociception typical of humans or other mammals, a circumstance according well with the absence of the specialized cortical regions necessary for pain in humans;
* Recent claims for consciousness in fishes are evaluated, but found to lack adequate supporting evidence, neurological feasibility, or the likelihood that consciousness would be adaptive;
* Even if fishes were conscious, it is unwarranted to assume that they possess a human-like capacity for pain;
* Overall, the behavioral and neurobiological evidence reviewed shows fish responses to nociceptive stimuli are limited and fishes are unlikely to experience pain.
PDF available. Those interested please let me know.
Reference:
Rose, J. D., R. Arlinghaus, S. J. Cooke, B. K. Diggles, W. Sawynok, E. D. Stevens, & C. D. L. Wynne (2014). Can fish really feel pain? Fish and Fisheries, 15:97-133.
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Fascinating articles Marcos!! Keep 'em coming! :+ cred:
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Hi Marcos
May I have a copy of the barotrauma article please. Thank you for this thread, top of the range.
:corrct:
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Thanks, guys. Hope they are somehow helpful.
@Greg, email sent.
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Changing relative abundance and behaviour of silky and grey reef sharks baited over 12 years on a Red Sea reef
* There is a lack of studies on how provisioning may influence shark numbers and behaviour.
* The effects of long-term provisioning were investigated at a Red Sea reef, where both grey reef shark and silky shark occurred.
* Initially, grey reef sharks outnumbered silky sharks, but over 6 years, silky shark numbers increased almost 20-fold, whereas grey-reef sightings decreased >90%.
* Following this, silky-shark sightings also declined considerably (>80%).
* It is suggested that these declines could relate to local overfishing.
* Sighting records indicated that provisioning extended the residency of transient individuals.
* Conversely, the site fidelity typical of grey reef sharks would have made them more susceptible to local depletion. Silky sharks were recorded as behaving more boldly when present in greater numbers, but the decline in grey reef sharks appears to be unrelated to the initial increase in the numbers of silky shark.
PDF available.
Reference:
Clarke, C. R., J. S. E. Lea & R. F. G. Ormond (2013). Changing relative abundance and behaviour of silky and grey reef sharks baited over 12 years on a Red Sea reef. Marine and Freshwater Research, 64: 909-919.
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Agricultural impact on the pelagic ecosystem of the small temporarily open/closed Seteni Estuary, South Africa
* The catchment of the Seteni Estuary, a small intermittently open estuary in South Africa, has been under extensive sugar cultivation for over 60 years.
* The study aimed to determine the impact of agriculturally derived nutrients on its pelagic communities.
* The main effects, thus far, being evident in the exceptionally high nitrogen concentrations and imbalance in nutrient ratios.
* Despite this, the system remains largely functional.
* There is potential for deterioration should the catchment become more nutrient-rich through poor management or land-use changes.
PDF available.
Referrence:
Carrasco, N. K. , R. Perissinotto & A. Whitehead (2013). Agricultural impact on the pelagic ecosystem of the small temporarily open/closed Seteni Estuary, South Africa. Marine and Freshwater Research, 64: 938-950.
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:+ cred: Marcos.
I cannot even put into words how important this info is. (As in all the posts you've made here). Very well done. Please continue, it is great to read this.
Cheers
Robin
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Thank you for a very informative thread!
Do these articles come from one journal?
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Thank you for a very informative thread!
Do these articles come from one journal?
No. These are published on several different journals. If you look at each paper's abstract I posted there's the full reference of the paper at the end i.e. authors, year of publication, title, the journal's name and volume, then pages. The last one for example was published on an Ausie journal called Marine & Freshwater Research. Quite a few of them are from the African Journal of Marine Science, for obvious reasons.
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Thank you john if only I could read...
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Humpback dolphin bycatch in the shark nets in KwaZulu-Natal, South Africa
* Humpback dolphins (Sousa plumbea) in South Africa are classified as Vulnerable and one quantifiable threat is accidental mortality in the shark nets in KwaZulu-Natal.
* The spatial, temporal and life history patterns of this bycatch to guide mitigation strategies to decrease humpback dolphin capture were investigated.
* A total of 203 individuals were caught between 1980 and 2009.
* Most catches (61%) occurred at Richards Bay in the northern part of their distribution in South Africa.
* Annual catch rate fluctuated considerably and there was little seasonality.
* The sex ratio was male-biased (1.55:1) and in particular skewed towards adolescents (56%) which constituted the majority of the catch.
* It is suggested that mitigation strategies be focused at Richards Bay, throughout the year.
* Of the existing shark net mitigation strategies, changing fishing gear from nets to baited hooks (drumlines) could be useful to decrease humpback dolphin capture rates.
PDF available.
Reference
Atkins, S., G. Cliff & N. Pillay (2013). Humpback dolphin bycatch in the shark nets in KwaZulu-Natal, South Africa. Biological Conservation, 159: 442-449.
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Feeding ecology of bull sharks (Carcharhinus leucas) in the coastal waters of the Southwest Indian Ocean
* As apex predators, sharks play an important role shaping their respective marine communities through predation and
associated risk effects
* Understanding the predatory dynamics of sharks within communities is, therefore, necessary to establish effective ecologically based conservation strategies
* Non-lethal sampling methods were used to investigate the feeding ecology of bull (=Zambezi) sharks (Carcharhinus leucas) using stable isotope analysis within a subtropical marine community in the southwest Indian Ocean (Ponta do Ouro)
* The main objectives of this study were to investigate and compare the predatory role that sub-adult and adult bull sharks play within a top predatory teleost fish community.
* Bull sharks had significantly broader niche widths compared to top predatory teleost assemblages
* This suggests that bull sharks forage from a more diverse range of sources over a wider geographical range than the predatory teleost community
* Adult bull sharks appeared to exhibit a shift towards consistently higher trophic level prey from an expanded foraging range
compared to sub-adults, possibly due to increased mobility linked with size
* Although predatory teleost fish are also capable of substantial migrations, bull sharks may have the ability to exploit a more diverse range of habitats and appeared to prey on a wider diversity of larger prey
* This suggests that bull sharks play an important predatory role within their respective marine communities and adult sharks in particular may shape and link ecological processes of a variety of marine communities over a broad range.
PDF available.
Reference:
Daly R., P.W Froneman & M.J. Smale (2013). Comparative Feeding Ecology of Bull Sharks (Carcharhinus leucas) in the Coastal Waters of the Southwest Indian Ocean Inferred from Stable Isotope Analysis. PLoS ONE 8(10): e78229
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Thank you for the information on this thread, I enjoy reading and filling my brain with information that most people find useless. This will go a long way with me. :+ cred:
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Global catches, exploitation rates, and rebuilding options for sharks
* Adequate conservation and management of shark populations is becoming increasingly important on a global scale, especially because many species are exceptionally vulnerable to overfishing.
*Yet, reported catch statistics for sharks are incomplete, and mortality estimates have not been available for sharks as a
group.
* The global catch and mortality of sharks from reported and unreported landings, discards, and shark finning are estimated at 1.44 million metric tons for the year 2000, and at only slightly less in 2010 (1.41 million tons).
* Based on an analysis of average shark weights, this translates into a total annual mortality estimate of about 100 million sharks in 2000, and about 97 million sharks in 2010, with a total range of possible values between 63 and 273 million sharks per year.
* Further, the exploitation rate for sharks as a group was estimated between 6.4% and 7.9% of sharks killed per year.
* This exceeds the average rebound rate for many shark populations, estimated from the life history information on 62 shark species (rebound rates averaged 4.9% per year), and explains the on going declines in most populations for which data exist.
* The consequences of these unsustainable catch and mortality rates for marine ecosystems could be substantial.
* Global total shark mortality, therefore, needs to be reduced drastically in order to rebuild depleted populations and restore marine ecosystems with functional top predators.
PDF available.
Reference:
Worm, B, B Davis, L Kettemer, CA Ward-Paige, D Chapman, MR Heithaus, ST Kessel & SH Gruber (2013). Global catches, exploitation rates, and rebuilding options for sharks. Marine Policy 40: 194-204.
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Southern African Marine Linefish Species Profiles
* This publication is a compilation of species profiles for 139 important marine linefish species from 38 families caught in southern African waters, including both teleosts and elasmobranchs.
* It provides a comprehensive update of a previous edition published in 2000.
* Where available, referenced information for each species is presented on distribution, movement, habitat, feeding, reproduction, biometrics, fishery, biological reference points, stock status, vulnerability, current regulations, management considerations and research requirements.
* Each profile is intended to be an up-to-date summary of what is currently known about the species in order to help users, managers and scientists to determine effective management plans, to ensure the future conservation and sustainable use of each species.
PDF available here (http://www.ori.org.za/uploads/files/Southern_African_Marine_Linefish_Species_Profiles.pdf (http://www.ori.org.za/uploads/files/Southern_African_Marine_Linefish_Species_Profiles.pdf)) or PM me.
Reference
Mann, B. (ed) (2013). Southern African marine linefish species profiles. ORI Special Publication, 9: 343pp.
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The first population estimate for white sharks in South Africa using photo identification and automated software
* South Africa is reputed to host the world’s largest remaining population of white sharks, yet no studies have accurately
determined a population estimate based on mark-recapture of live individuals.
* Dorsal fin photographs (fin IDs) were used to identify white sharks in Gansbaai, South Africa, from January 2007 – December 2011.
* The computer programme DARWIN was used to catalogue and match fin IDs of individuals; this is the first study to successfully use the software for white shark identification.
* The programme performed well despite a number of individual fins showing drastic changes in dorsal fin shape over time.
* Of 1682 fin IDs used, 532 unique individuals were identified.
* The superpopulation size was estimated at 908 (95% confidence interval 808–1008).
* This estimated population size is considerably larger than those described at other aggregation areas of the species and is comparable to a previous South African population estimate conducted 16 years prior.
* The assessment suggests the species has not made a marked recovery since being nationally protected in 1991.
* As such, additional international protection may prove vital for the long-term conservation of this threatened species.
PDF available
Reference
Towner, A. V., M. A. Wcisel, R. R. Reisinger, D. Edwards & O. J. D. Jewell (2013). Gauging the threat: The first population estimate for white sharks in South Africa using photo identification and automated software. PLoS ONE, 8 (6): e66035.
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* The assessment suggests the species has not made a marked recovery since being nationally protected in 1991.
Wow, fascinating! And contrary to popular belief amongst anglers!
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I thought that would catch the interest of many! Yeap, interesting how things turn out, hey?
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Opens up ones eyes, superb read Marcos!
What I find interesting is the total disc width of the Blue Ray is still recorded at 75cm's... I know of so many Blue Rays caught that are wider than that.
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Opens up ones eyes, superb read Marcos!
What I find interesting is the total disc width of the Blue Ray is still recorded at 75cm's... I know of so many Blue Rays caught that are wider than that.
Thing is WK scientists must work with published records for credibility ... so you better start publishing your findings :hehe:
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:hehe: I have a photo of a pregnant fm Blue Ray, DW 90cm...
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Humpback dolphin bycatch in the shark nets in KwaZulu-Natal, South Africa
* Humpback dolphins (Sousa plumbea) in South Africa are classified as Vulnerable and one quantifiable threat is accidental mortality in the shark nets in KwaZulu-Natal.
* The spatial, temporal and life history patterns of this bycatch was investigated to guide mitigation strategies to decrease humpback dolphin capture.
* A total of 203 individuals were caught between 1980 and 2009.
* Patterns of captures in relation to the area of capture (location) and year and month of retrieval from the nets were analysed, as well as the distribution of the sex and size (body length) of humpback dolphins.
* Most catches (61%) occurred at Richards Bay in the northern part of their distribution in South Africa.
* Annual catch rate fluctuated considerably and there was little seasonality.
* The sex ratio was male-biased (1.55:1) and in particular skewed towards adolescents (56%) which constituted the majority of the catch.
* It is suggest that mitigation strategies be focused at Richards Bay, throughout the year.
* Of the existing shark net mitigation strategies, changing fishing gear from nets to baited hooks (drumlines) could be useful to decrease humpback dolphin capture rates.
PDF available.
Reference
Atkins, S., G. Cliff & N. Pillay (2013). Humpback dolphin bycatch in the shark nets in KwaZulu-Natal, South Africa. Biological Conservation, 159: 442-449.
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An evaluation of the injury and short-term survival of bonefish as influenced by a mechanical lip-gripping device
* Mechanical lip-gripping devices are becoming popular among recreational anglers as a means of holding fish for hook removal and photos prior to release in an effort to minimize scale or slime loss from handling.
* There has been no actual evaluation of the consequences of using such a device on the health and survival of the fish.
* Using wild adult bonefish (Albula spp.) as the test organism, we assessed the impact of a commonly used mechanical lip-gripping device on fish injury, behavior, and survival in a seawater laboratory.
* Although no fish died after 48 h, the lip-gripping device caused mouth injuries to 80% of bonefish restrained in the water and 100% of bonefish held in the air, always when fish thrashed while being held.
* Some of the injuries were severe (40%) and included separating the tongue from the floor of the mouth, creating tears and holes in the soft tissue of the lower jaw, and splitting the mandible.
* Anglers should use caution when using mechanical lip-gripping devices for bonefish, at least until additional studies are conducted to help tease apart how the risk of injury using mechanical lip-gripping devices on less exhausted individuals compares to the risk of post-release mortality for fish exercised to exhaustion.
Not so recent but still interesting! PDF available.
Reference:
Danylchuk, A. J., A. Adams, S. J. Cooke & C. D. Suski (2008). An evaluation of the injury and short-term survival of bonefish (Albula spp.) as influenced by a mechanical lip-gripping device used by recreational anglers. Fisheries Research, 93: 248-252.
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That is interesting John... thanks. I have noticed that the are different lips grips and some seem better designed that others with more rounded grips and better quality. I wonder if a better design/quality would do less damage and if the guys testing them used different makes/models and actually considered this.
Thanks again
7/10
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According to the paper they only used one type of grip (no brand mentioned).
This is what they used
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Thanks John... I have a Berkley one with a digital scale and it has flat and rather sharp jaws. I Googled some and got these images of some that seem to be designed to protect the fish with balls or larger gripping area... I can only see a benefit in this design. but who knows. I was blown away to see the number of designs when I googled fish grip images!
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Whales from space: Counting southern right whales by satellite
* A method of identifying and counting whales using very high resolution satellite imagery through the example of southern right whales breeding in part of the Golfo Nuevo, Península Valdés in Argentina is described.
* Southern right whales have been extensively hunted over the last 300 years and although numbers have recovered from near extinction in the early 20th century, current populations are fragmented and are estimated at only a small fraction of pre-hunting total.
* Recent extreme right whale calf mortality events at Península Valdés, which constitutes the largest single population, have raised fresh concern for the future of the species.
* The WorldView2 satellite has a maximum 50 cm resolution and a water penetrating coastal band in the far-blue part of the spectrum that allows it to see deeper into the water column.
* Using an image covering 113 km2, we identified 55 probable whales and 23 other features that are possibly whales, with a further 13 objects that are only detected by the coastal band.
* Comparison of a number of classification techniques, to automatically detect whale-like objects, showed that a simple thresholding technique of the panchromatic and coastal band delivered the best results.
* This is the first successful study using satellite imagery to count whales; a pragmatic, transferable method using this rapidly advancing technology that has major implications for future surveys of cetacean populations.
PDF available.
Reference
Fretwell, P. T., I. J. Staniland & J. Forcada (2014). Whales from space: Counting southern right whales by satellite. PLoS ONE, 9 (2): e88655.
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Opposite latitudinal gradients in projected ocean acidification and bleaching impacts on coral reefs
* Coral reefs and the services they provide are seriously threatened by ocean acidification and climate change impacts like coral bleaching.
Updated global projections for these key threats to coral reefs based on ensembles of IPCC AR5 climate models using the new Representative Concentration Pathway (RCP) experiments, are presented.
* For all tropical reef locations, absolute and percentage changes in aragonite saturation state (Ωarag) are projected for the period between 2006 and the onset of annual severe bleaching (thermal stress >8 degree heating weeks); a point at which it is difficult to believe reefs can persist as we know them.
* Severe annual bleaching is projected to start 10–15 years later at high-latitude reefs than for reefs in low latitudes under RCP8.5.
* In these 10–15 years, Ωarag keeps declining and thus any benefits for high-latitude reefs of later onset of annual bleaching may be negated by the effects of acidification.
* There are no long-term refugia from the effects of both acidification and bleaching.
* Of all reef locations, 90% are projected to experience severe bleaching annually by 2055.
* Furthermore, 5% declines in calcification are projected for all reef locations by 2034 under RCP8.5, assuming a 15% decline in calcification per unit of Ωarag.
* Drastic emissions cuts, such as those represented by RCP6.0, result in an average year for the onset of annual severe bleaching that is ~20 years later (2062 vs. 2044).
* However, global emissions are tracking above the current worst-case scenario devised by the scientific community, as has happened in previous generations of emission scenarios.
* The projections here for conditions on coral reefs are dire, but provide the most up-to-date assessment of what the changing climate and ocean acidification mean for the persistence of coral reefs.
PDF available.
Reference
van Hooidonk, R., J. A. Maynard, D. Manzello & S. Planes (2014). Opposite latitudinal gradients in projected ocean acidification and bleaching impacts on coral reefs. Global Change Biology, 20: 103-112.
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Very interesting John F! Keep them coming! :+ cred:
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Reefz, at this stage I think it is actually scary! The latest IPCC report draws a bleak picture in terms of climate change for the next 100 years. I'm afraid our children and grand-children will inherit a pretty messed-up planet!
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Socio-economic aspects of the Sodwana Bay SCUBA diving industry, with a specific focus on sharks
* Understanding socio-economic aspects of the diving industry at Sodwana Bay, including data on participant motivation and expenditure, is crucial for the effective management of the St Lucia and Maputaland marine protected areas, South Africa.
* Between July 2011 and July 2012 a total of 59 553 dives was conducted by 15 780 divers.
* Data were collected by means of the administration of a semi-structured survey questionnaire to 750 dive participants.
* Participant responses indicated that the direct value of diving to the iSimangaliso Wetland Park was R75 484 784.
* The majority of dives at Sodwana were on coral-covered sandstone reefs (95.2%), with shark diving accounting for only 4.8% of dives.
* Although sharks were not the primary attraction for divers to visit Sodwana, 84.2% of respondents stated that they were interested in shark diving and that more opportunities to dive with sharks would encourage them to revisit Sodwana more often.
* Attaching an economic value to sharks as a dive attraction to Sodwana and highlighting their potential for the growth of the dive industry may act as leverage for their protection against fishing within iSimangaliso.
pdf available.
Reference:
Dicken, M. L. (2014). Socio-economic aspects of the Sodwana Bay SCUBA diving industry, with a specific focus on sharks. African Journal of Marine Science, 36: 39-47.
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Selective exploitation of fish populations by recreational anglers may lead to evolutionary downsizing of adults
* When gene flow is limited and harvesting is intensive, fishing may alter life histories and favour trait combinations that collectively reduce adult body size;
* However, empirical evidence of downsizing of adults in small-bodied coastal fish is still scarce, in part due to the lack of knowledge about the selective nature of certain fishing gears, such as recreational angling, and the difficulties in estimating the dispersion of pelagic early-life stages;
* Using the small-bodied sedentary coastal marine fish Serranus scriba as a model, it is empirically shown that:
* Recreational angling selects for life-history traits (i.e. increased reproductive investment) that promote downsizing of adults;
* Second, using Lagrangian particle dispersion modelling, we show how local hydrodynamics generates patterns of limited connectivity and the emergence of meta-population structure;
* Finally, the life histories presently observed in isolated populations of S. scriba that experienced differential fishing pressure matched expectations of fishing-induced downsizing of adult body size.
* Body size is an important trait in aquatic food webs, and evolutionary downsizing might have unforeseen consequences.
* From a precautionary perspective, maintaining the metapopulation structure and the full range of genotypes inherent in them is important, even for small-bodied, geographically restricted fish species that are mainly harvested by recreational anglers.
PDF available.
Reference:
Alós, J., M. Palmer, I. A. Catalan, A. Alonso-Fernández, G. Basterretxea, A. Jordi, L. Buttay, B. Morales-Nin & R. Arlinghaus
(2014). Selective exploitation of spatially structured coastal fish populations by recreational anglers may lead to evolutionary downsizing of adults. Marine Ecology Progress Series, 503: 219-233.
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Thank you John, I remember reading somewhere that size restrictions on commercial species caused them to spawn at a younger age/size. Will look for the study but I cant remember where I saw it.
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75 million on diving alone in one year at Sodwana!! :shk Serious industry that!
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Google never forgets:
http://www.nature.com/news/ocean-conservation-a-big-fight-over-little-fish-1.12325 (http://www.nature.com/news/ocean-conservation-a-big-fight-over-little-fish-1.12325)
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Thank you John, I remember reading somewhere that size restrictions on commercial species caused them to spawn at a younger age/size. Will look for the study but I cant remember where I saw it.
Yeap... classical signs of overfishing...
i) decrease in CPUE
ii) decrease in average size of the fish
iii) shift in the catch composition
iv) fish start reproducing at younger age/size
v) fishery collapse
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Just reading through from the beginning of the thread here and one cannot help but thinking that we know so little of what is really happening in our oceans and what the future holds for us recreational fisherman.
I unfortunately disagree with much of what may be regarded as factual evidence and what is mere speculation on the part of scientists and researchers , regarding many specific case studies and the resultant methods that are employed to conserve species
What is most evident is that so much more research is required , and it is only through the combined efforts of every person who has any involvement with taking anything from our oceans (and this includes the final consumers (which includes 'chickens' ) to wake up to the realities that fish stocks are dwindling at an alarming rates world wide.
Although the impact of recreational fishermen cannot summarily be discarded in contributing to this , in my opinion , governmental regulations, as far as commercial fisheries , has by far the greatest effect on the overall picture , that we , the recreational fishermen , will ever contribute to these unfortunate statistics.
At the end of the day , for me everything relates back to wise and sustainable ecosystem management , and here governments in my opinion , are failing dismally- the underlying factors for this is to much blah blah blah and far to little contributions from their side in the way of resources and money allocated to get more research underway...get this right , then there is possibly a future for us to continue doing what we enjoy
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Response of fish communities to the deployment of estuarine artificial reefs for fisheries enhancement
* Artificial reef systems constructed in three south-eastern Australian estuaries were monitored over a four-year period;
* Recruitment of fish to the artificial reefs was rapid, with significantly greater species richness observed on artificial reefs than on natural habitats for the majority of locations and times;
* The rate of community change varied between estuaries and appeared to be related to the quality and amount of existing habitat and the distance of the artificial reef from sources of recruitment;
* General patterns were also identified among estuaries driven by strong recruitment, followed by a rapid reduction in several mobile schooling species.
* By contrast, there was early and sustained recruitment of a variety of sparid species, which are of importance to recreational and commercial fisheries.
PDF available.
Reference:
Lowry, M. B., T. M. Glasby, C. A. Boys, H. Folpp, I. Suthers & M. Gregson (2014). Response of fish communities to the deployment of estuarine artificial reefs for fisheries enhancement. Fisheries Management and Ecology, 31: 42-56.
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Thirty years of monitoring traditional fish trap catches at Kosi Bay, KwaZulu-Natal, South Africa, and management implications
* The catches of the traditional fish traps in the Kosi Bay estuarine lakes were monitored over a 30-year period from 1981 to 2010;
* Monitoring data were used to provide estimates of, and insights into, catch size and species composition as well as seasonal and annual cycles of catch abundance;
* Over 1.2 million fish, comprising 43 species and 23 families, were estimated to have been caught during the study period.
* Tag-and-release data were used to estimate the impact of trap fishing on fish stocks and comparisons were made with recreational fishing to indicate overall fishing pressure and the sustainability of the fishing;
* Trap numbers remained fairly similar from the first year of monitoring (1981) until 1994, but thereafter they more than trebled by 2001; although numbers decreased after this, they remained well above earlier levels;
* During this period, recreational angling was an important factor, and gillnetting - both legal and illegal - added to the fishing pressure;
* Information from the fish trap monitoring, together with results from fish mark and recapture studies, suggest a very high, and possibly unsustainable, catch rate that requires management intervention to return them back to historical and sustainable levels.
PDF available.
Reference:
Kyle, R. (2013). Thirty years of monitoring traditional fish trap catches at Kosi Bay, KwaZulu-Natal, South Africa, and management implications. African Journal of Marine Science, 35: 67-78.
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30 years study! but will anyone take action or will we need further study ...
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30 years study! but will anyone take action or will we need further study ...
:corrct: The info to support management is there... :-(
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We have caught very few fish on our last trips to Kosi. With 3 boats and 9 anglers we did little better than put fish on the table for meals :cry: . The gillies saw '' fishermen'' on boats buying rock salmon from the traps :nuts: . IMO many traps are used to keep the fish alive/fresh until bakkies arrive to buy and transport the fish caught in the gill nets' I was was told that the nets are are up to 300m in length . We saw the bakkies on most days, parked under trees next to the traps on 2nd lake, The gillies say this is normal practice.
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Marcos please could you mail me that pdf :pray:
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Assessment of the Trachinotus botla shore-fishery in KwaZulu-Natal, South Africa
* The shore-fishery for Trachinotus botla in KwaZulu-Natal appears to be in a stable state.
* A per-recruit assessment showed that the species is currently underexploited (spawner biomass-per-recruit = 75% of pristine levels) and that fishing mortality could theoretically be increased.
* The fishery was shown to display considerable spatial and temporal variability with resource abundance increasing north-easterly towards Mozambique with catch per unit effort (CPUE) peaking during summer.
* Trachinotus botla displayed random movement patterns indicative of a surf-zone resident, with 78% of the recaptures being made within 1 km of the tagging site.
* The movement pattern observed was not affected by fish size or time at liberty.
* An increasing trend in mean annual CPUE since 2002 suggests that either the resource is increasing since the promulgation of the ban on beach driving or possibly as a result of increased targeting of this species using a relatively modern technique known locally as ‘dropshot’ fishing.
* It is likely that the beach driving ban has shifted fishing effort to accessible nodes along the coast where there is some evidence of localised overexploitation.
PDF available.
Reference:
Parker, D., A. J. Booth & B. Q. Mann (2013). A spatio-temporal assessment of the Trachinotus botla shore-fishery in KwaZulu-Natal, South Africa. African Journal of Marine Science, 35: 35-46.
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Using posts to an online social network to assess fishing effort
* Fisheries management has evolved from reservoir to watershed management, creating a need to simultaneously
gather information within and across interacting reservoirs.
* However, costs to gather information on the fishing effort on multiple reservoirs using traditional creel methodology are often prohibitive.
* Angler posts about reservoirs online provide a unique medium to test hypotheses on the distribution of fishing pressure.
* It is shown that the activity on an online fishing social network is related to fishing effort and can be used to facilitate management goals.
* The Nebraska Fish and Game Association Fishing Forum was searched for all references from April 2009 to December 2010 to 19 reservoirs that comprise the Salt Valley regional fishery in southeastern Nebraska.
* The number of posts was positively related to monthly fishing effort on a regional scale, with individual reservoirs having the most annual posts also having the most annual fishing effort.
* Furthermore, this relationship held temporally. Online fishing social networks provide the potential to assess effort on larger spatial scales than currently feasible.
pdf available.
Reference:
Martin, D. R., C. J. Chizinski, K. M. Eskridge & K. L. Pope (2014). Using posts to an online social network to assess fishing effort. Fisheries Research, 157: 24-27.
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Residency Patterns and Migration Dynamics of Adult Bull Sharks on the East Coast of Southern Africa
* Bull sharks (Carcharhinus leucas) are globally distributed top predators that play an important ecological role within coastal marine communities;
* However, little is known about the spatial and temporal scales of their habitat use and associated ecological role;
* In this study, passive acoustic telemetry was employed to investigate the residency patterns and migration dynamics of 18 adult bull sharks (195–283 cm total length) tagged in southern Mozambique for a period of between 10 and 22 months;
* The majority of sharks (n = 16) exhibited temporally and spatially variable residency patterns interspersed with migration events;
* Ten individuals undertook coastal migrations that ranged between 433 and 709 km (mean = 533 km) with eight of these sharks returning to the study site;
* During migration, individuals exhibited rates of movement between 2 and 59 km.d21 (mean = 17.58 km.d21) and were recorded travelling annual distances of between 450 and 3760 km (mean = 1163 km);
* Migration towards lower latitudes primarily took place in austral spring and winter and there was a significant negative correlation between residency and mean monthly sea temperature at the study site;
* This suggested that seasonal change is the primary driver behind migration events but further investigation is required to assess how foraging and reproductive activity may influence residency patterns and migration;
* Results from this study highlight the need for further understanding of bull shark migration dynamics and suggest that effective conservation strategies for this vulnerable species necessitate the incorporation of congruent trans-boundary policies over large spatial scales.
PDF available.
Reference:
Daly, R., M. J. Smale, P. D. Cowley & P. W. Froneman (2014). Residency patterns and migration dynamics of adult bull sharks (Carcharhinus leucas) on the East coast of southern Africa. PLoS ONE, 9(10): e109357.
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Seagrasses in the age of sea turtle conservation and shark overfishing
* Efforts to conserve globally declining herbivorous green sea turtles have resulted in promising growth of some populations.
* These trends could significantly impact critical ecosystem services provided by seagrass meadows on which turtles feed.
* Expanding turtle populations could improve seagrass ecosystem health by removing seagrass biomass and preventing of the formation of sediment anoxia.
* However, overfishing of large sharks, the primary green turtle predators, could facilitate turtle populations growing beyond historical sizes and trigger detrimental ecosystem impacts mirroring those on land when top predators were extirpated.
* Experimental data from multiple ocean basins suggest that increasing turtle populations can negatively impact seagrasses, including triggering virtual ecosystem collapse.
* Impacts of large turtle populations on seagrasses are reduced in the presence of intact shark populations.
* Healthy populations of sharks and turtles, therefore, are likely vital to restoring or maintaining seagrass ecosystem structure, function, and their value in supporting fisheries and as a carbon sink.
PDF available.
Reference Type: Journal Article
Heithaus, M. R., T. Alcoverro, R. Arthur, D. A. Burkholder, K. A. Coates, M. J. A. Christianen, N. Kelkar, S. A. Manuel, A. J. Wirsing, W. J. Kenworthy & J. W. Fourqurean (2014). Seagrasses in the age of sea turtle conservation and shark overfishing. Frontiers in Marine Science, 1: 6 pp.
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Catch rates and income are associated with fisheries management restrictions and not an environmental disturbance, in a heavily exploited tropical fishery
* The influence of the largest temperature anomaly in recent history, the 1997-1998 El Niño-Indian Ocean Dipole anomaly that killed half of the corals in the Indian Ocean, with a nearly coincident increase in fisheries management restrictions on coral reef fisheries in southern Kenya was evaluated and compared;
* Seawater temperatures, benthic primary producers, and fishing effort and catch rate and income time series collected over the 1993-2012 period were evaluated using time series and variable cointegration methods;
* An observed decline and subsequent increase in catch rates was closely associated with the implementation of increasing fisheries restrictions and was not predictably cointegrated with the temperature or the primary producer’s time series;
* This may have occurred because the disturbance was pulsed with a limited 6 yr impact on the primary producers and the fishery was heavily utilized and composed of fast-growing generalist species with broad diet and habitat needs
* Consequently, under these conditions, promoting fisheries restrictions is expected to attenuate the predicted declines in fish catches projected by global warming.
PDF available.
Reference
McClanahan, T. R. & C. A. Abunge (2014). Catch rates and income are associated with fisheries management restrictions and not an environmental disturbance, in a heavily exploited tropical fishery. Marine Ecology Progress Series, 513: 201-213.
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Not really fisheries, but...
Plastic Pollution in the World’s Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea
* Plastic pollution is ubiquitous throughout the marine environment, yet estimates of the global abundance and weight of floating plastics have lacked data, particularly from the Southern Hemisphere and remote regions.
* An estimate of the total number of plastic particles and their weight floating in the world’s oceans from 24 expeditions (2007–2013) across all five sub-tropical gyres, costal Australia, Bay of Bengal and the Mediterranean Sea conducting surface net tows (N5680) and visual survey transects of large plastic debris (N5891) is reported.
* Using an oceanographic model of floating debris dispersal calibrated by our data, and correcting for wind-driven vertical mixing, a minimum of 5.25 trillion particles weighing 268,940 tons is estimated.
* When comparing between four size classes, two microplastic <4.75 mm and meso- and macroplastic > 4.75 mm, a tremendous loss of microplastics is observed from the sea surface compared to expected rates of fragmentation, suggesting there are mechanisms at play that remove <4.75 mm plastic particles from the ocean surface.
PDF available
Reference:
Eriksen, M., L. C. M. Lebreton, H. S. Carson, M. Thiel, C. J. Moore, J. C. Borerro, F. Galgani, P. G. Ryan & J. Reisser (2014). Plastic pollution in the world’s oceans: More than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea. PLoS ONE, 9 (12): e111913.
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Post-release mortality in istiophorid billfish
* Meta-analysis (inverse-variance, random-effects model) involving 46 studies was used to estimate the effect size of post-release mortality (Fr) in six istiophorid billfish species (black marlin Istiompax indica, blue marlin Makaira nigricans, longbill spearfish Tetrapturus pfluegeri, sailfish Istiophorus platypterus, striped marlin Kajikia audax, and white marlin K. albida) following release from recreational, longline, and harpoon fishing gears.
* The studies involved 400 reporting pop-up satellite archival tags and 64 reporting acoustic (ultrasonic) tags.
* Despite fish being captured, tagged, and released under widely disparate conditions, locations, and gear types; Fr was homogeneous between species.
* Variability in Fr was principally due to random sampling error within studies with no evident patterns.
* Fifteen studies (33% of tags) indicated no mortality and the overall summary effect size for Fr was 13.5% (95% CI: 10.3 – 17.6%).
* Since the random-effects model decomposed to a fixed-effect model when the between-studies variance T2 = 0.00; results were confirmed using exact nonparametric inferential tests and sensitivity analyses.
* The results support earlier findings in the Atlantic and substantiate the majority of istiophorid billfish survive when released from recreational and longline fishing gear, clearly implying catch-and-release as a viable management option that permits fishing activity while protecting parental biomass and the fishery.
PDF available.
Reference:
Musyl, M. K., C. D. Moyes, R. W. Brill, B. L. Mourato, A. West, L. M. McNaughton, W.-C. Chiang & C.-L. Sun (in press). Post-release mortality in istiophorid billfish. Canadian Journal of Fisheries and Aquatic Sciences, 10.1139/cjfas-2014-0323
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This is a really important piece of research. It basically says that only 13.5% of the billfish released dies... irrespective of species, conditions, bleeding, etc, etc.
So, the argument "the fish was badly hooked (or was bleeding badly) and would not survive, so we landed it!", holds even less water!!!!!
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Aspects of the biology and life history of largespot pompano, Trachinotus botla, in South Africa
* Trachinotus botla is an important recreational surf zone-dependent fish species distributed in the Indo-west Pacific from South Africa to Australia.
* In South Africa it is restricted to the northern KwaZulu-Natal coast.
* Biological investigations revealed that it is a fast growing species that attains a maximum age of ~7 years.
* Males and females sexually matured in their third year.
* It has a protracted summer spawning season with evidence of serial spawning behaviour.
* T. botla is an opportunistic predator with a generalist diet, with fish feeding on a wide variety of prey items particularly those that are temporally ‘superabundant’.
* Small fish fed predominantly on copepods and terrestrial insects, whereas larger fish consumed bivalves and crabs.
* Teleosts, primarily engraulids, were important components to the diet of fish of all sizes.
* An ontogenetic dietary shift was observed just after sexual maturity (~300-mm fork length) that is possibly linked to a change in habitat preference with larger fish foraging on deeper reefs.
PDF available.
Reference:
Parker, D. & A. J. Booth (2015). Aspects of the biology and life history of largespot pompano, Trachinotus botla, in South Africa. Marine and Freshwater Research, 66(3): 247-255.
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Movement patterns of surf-zone fish species in a subtropical marine protected area on the east coast of South Africa
* A long-term mark-recapture study was used to assess the movement patterns of surf-zone fishes in the St Lucia Marine Reserve, a marine protected area within the iSimangaliso Wetland Park, a World Heritage Site on the east coast of South Africa.
* Between 2001 and 2013, 6 613 fish from 71 species, caught by hook and line, were tagged at four sites within and adjacent to a no-take marine sanctuary area.
* A total of 1 004 (15.2%) recaptures were made from 17 species.
* The majority (82.4%) of these species displayed station-keeping behaviour, whereas only three were classified as wider-ranging species, and no species with discernible migratory behaviour was observed.
* Findings for five species with the highest recapture rates, namely Pomadasys furcatus, Epinephelus andersoni, E. marginatus, Dinoperca petersi and Lutjanus rivulatus, are presented in greater detail.
* Recapture rates ranged from 7% to 50% and time at liberty from 0 to 3 163 days.
* Individuals of all five species displayed station-keeping behaviour, with the 95th percentile of intra-study-site movements varying between 200 and 1 025 m (linear distance).
* However, four of the five species also displayed some ranging behaviour and made exploratory excursions ranging from 3.5 to 125 km, in both northerly and southerly directions.
* The dominance of stationkeeping behaviour suggests that the St Lucia Marine Reserve sanctuary zone provides an important refuge for these species, with some export to adjacent areas.
pdf available
Reference:
Mann, B. Q., P. D Cowley & S. T. Fennessy (2015). Movement patterns of surf-zone fish species in a subtropical marine protected area on the east coast of South Africa. African Journal of Marine Science, 37: 99-114.
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Scientists discover first warm-bodied fish!!!!!
http://news.sciencemag.org/biology/2015/05/scientists-discover-first-warm-bodied-fish?utm_source=facebook&utm_medium=social&utm_campaign=facebook (http://news.sciencemag.org/biology/2015/05/scientists-discover-first-warm-bodied-fish?utm_source=facebook&utm_medium=social&utm_campaign=facebook)
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Fascinating!
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Just spotted an article on Biznews about the Opah and looks like it's taken the fancy of some chefs... "This discovery is surprising since the opah is large and conspicuous; indeed, it’s already a favourite in fish markets and restaurants. Wegner and his colleagues deserve great credit for recognising and describing in detail the specialised gill heat exchangers that have been hidden right under the noses of fishermen and chefs for centuries."
I hope it doesn't become over exploited because of it's uniqueness.
http://www.biznews.com/light/2015/05/15/the-moonfish-first-warm-blooded-fish-and-a-favourite-in-markets-restaurants/
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Less fish on the hooks does not necessarily mean less fish in the sea
To avoid overfishing and aid in sustainable exploitation, the status of the fish stocks has to be monitored regularly. In many cases stock assessment is based on fishery-dependent data generated from fish markets or creel surveys. The assumption is: the lower the catches in a certain unit of time, the smaller the stock of fish should be. Biologists have now shown that some fish species show enhanced gear-avoidance behavior in regions with high angling intensity compared to fish exposed to low levels of exploitation near marine protected areas.
Reference:
Forschungsverbund Berlin e.V. (FVB). "Clever fish around the coast of Mallorca Island avoid fishing lines." ScienceDaily. ScienceDaily, 20 May 2015. <www.sciencedaily.com/releases/2015/05/150520083129.htm>.
Article:
http://www.sciencedaily.com/releases/2015/05/150520083129.htm (http://www.sciencedaily.com/releases/2015/05/150520083129.htm)
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Wow... that Garrick was laughing at my lure the other day... now I know why hook avoidance and prolonged inspection must have revealed it was there to fool him... Very interesting. Thanks Icstuff...
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Scientists discover first warm-bodied fish!!!!!
http://news.sciencemag.org/biology/2015/05/scientists-discover-first-warm-bodied-fish?utm_source=facebook&utm_medium=social&utm_campaign=facebook (http://news.sciencemag.org/biology/2015/05/scientists-discover-first-warm-bodied-fish?utm_source=facebook&utm_medium=social&utm_campaign=facebook)
Big Fishes of the World: Lucky anglers catch THREE extremely rare OPAH fish in one day (http://www.youtube.com/watch?v=txvxxWQQ2-g#)
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Fish are smarter than we may think!!!!
By revealing that fish cooperate, cheat and punish, Redouan Bshary has challenged ideas about brain evolution
http://www.nature.com/news/animal-behaviour-inside-the-cunning-caring-and-greedy-minds-of-fish-1.17614?WT.ec_id=NATURE-20150528 (http://www.nature.com/news/animal-behaviour-inside-the-cunning-caring-and-greedy-minds-of-fish-1.17614?WT.ec_id=NATURE-20150528)
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Very interesting... I've always felt that animals in general have a whole lot more intelligence that we give them credit.
The two are such "bad boys" :hnthnt:
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:tkx: very interesting, I have heard many times that fish in heavily fished areas are much more wary of bait and visible line than those in isolated less frequented areas. Have also been told that a carp has roughly the intelligence of a domestic fowl and similar responses to frights and food , eg: they will eat slowly when alone, but will go into a frenzy when competition arrives. :dunno: :toppie:
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Parrotfish identified as major producers of island-building sediment in the Maldives
* Reef islands are unique landforms composed entirely of sediment produced on the surrounding coral reefs.
* Despite the fundamental importance of these ecological-sedimentary links for island development and future maintenance, reef island sediment production regimes remain poorly quantified.
* Using census and sedimentary data from Vakkaru island (Maldives), a sand-dominated atoll interior island, the major sediment-generating habitats, the abundance of sediment producers in these habitats, and the rates and size fractions of sediment generated by different taxa was quantified.
* The estimated annual sediment production is 685,000 kg (or 370 m3), ~75% of which is produced on the narrow outer reef flat, despite composing only 21% of the total platform area.
* Approximately 65% of the platform acts solely as a sediment sink.
* Census data identify parrotfish as the major sediment producers, generating >85% of the 5.7 kg/m2 of new sand-grade sediment produced on the outer reef flat each year.
* Halimeda (macroalgae) produce a further 10%, most as gravelgrade material.
* Comparisons between production estimates and sedimentary data indicate that reef ecology and island sedimentology are tightly linked; reef flat and lagoon sediments are dominated by coral and Halimeda, although fine- to medium-grained coral sand is the dominant (~59%) island constituent.
* The generation of sediment suitable for maintaining this reef island is thus critically dependent on a narrow zone of high-productivity reef, but most especially on the maintenance of healthy parrotfish populations that can convert reef
framework to sand-grade sediment.
PDF available.
Reference:
Perry, C. T., P. S. Kench, M. J. O’Leary, K. M. Morgan & F. Januchowski-Hartley (2015). Linking reef ecology to island building: Parrotfish identified as major producers of island-building sediment in the Maldives. Geology, 43: 503-506.
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Here's a nice site with daily news on marine biology and science in general.
http://www.sciencedaily.com/news/plants_animals/marine_biology/ (http://www.sciencedaily.com/news/plants_animals/marine_biology/)
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Red Map... an interesting app that helps keep track of how species are moving in response to climate change. It gives ordinary Oz citizens a chance to be part of science. Hopefully, it will extend around the globe and give us a better picture of how climate change is manifesting.
http://blogs.discovermagazine.com/citizen-science-salon/2015/06/19/science-behind-the-camera-snapping-pictures-for-climate-research/#.VYaah_mqqkr (http://blogs.discovermagazine.com/citizen-science-salon/2015/06/19/science-behind-the-camera-snapping-pictures-for-climate-research/#.VYaah_mqqkr)
And a short vid:
https://www.facebook.com/UniversityofTasmania/videos/10155634579945008/ (https://www.facebook.com/UniversityofTasmania/videos/10155634579945008/)
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Population structure of black musselcracker Cymatoceps nasutus: evidence for multiple populations in South African coastal waters
* Genetic studies on South African marine fishes have shown that many species exist as single, well-mixed stocks
throughout their core distribution;
* The black musselcracker or poenskop Cymatoceps nasutus is a slow-growing, late-maturing and long-lived sparid (Perciformes: Sparidae) that is endemic to South African coastal waters.
* Conventional tagging studies suggest that it is resident, with limited connectivity between different regions
along the coast;
Mitochondrial and nuclear DNA were used to investigate the genetic structure of C. nasutus along the South African coastline and showed evidence of at least two populations;
* Samples collected from the Tsitsikamma Marine Protected Area on the South Coast to KwaZulu-Natal on the East Coast showed no significant population structure over much of the distribution;
* Gene flow for C. nasutus within this region is not limited by geographic distance and appears to be unaffected by various oceanographic barriers and biogeographical boundaries;
* Samples from the Western Cape to the west of Tsitsikamma, however, showed moderate to substantial differentiation for both markers, which may be influenced by a temperature barrier – a coldwater ridge – along the South Coast;
* These data provide the first genetic assessment of this South African sparid, and suggest that a two-stock management strategy would be appropriate for the species.
PDF available.
Reference:
Murray, T. S., G. Gouws, M. Mwale, B. Q. Mann & P. D. Cowley (2014). Unravelling population structure of black musselcracker Cymatoceps nasutus: evidence for multiple populations in South African coastal waters. African Journal of Marine Science, 36: 493-503.
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Controlling outbreaks of the coral-eating crown-of-thorns starfish using a single injection of common household vinegar
* Outbreaks of the destructive coral-eating crown-of-thorns starfish, Acanthaster planci, present a considerable threat to coral reefs worldwide, and mitigating their impact has proven challenging.
* The most effective methods to control A. planci require injecting individual starfish with lethal chemicals.
* While some of these are highly effective, their administration often requires permits, training and access to specialised equipment. We aimed to identify a widely available and highly efficient alternative.
* It was discovered that common household vinegar is lethal to A. planci individuals when injected at the base of one their arms.
* A single injection of 25 ml vinegar induced functional mortality in <24 h and 100 % mortality in <48 h.
* These results demonstrate that vinegar is an effective alternative to currently used chemicals.
* Vinegar is a viable alternative in the toolkit of methods that can control and eradicate local outbreaks of COTS on coral reefs.
PDF available.
Reference:
Boström-Einarsson, L. & J. Rivera-Posada (2015). Controlling outbreaks of the coral-eating crown-of-thorns starfish using a single injection of common household vinegar. Journal: Coral Reefs. DOI 10.1007/s00338-015-1351-6.
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Thanks for sharing, Marcos. It is very interesting and I am sure the vinegar is a much more 'greener' and cheaper alternative.
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How sailfish use their bills to capture schooling prey
* The istiophorid family of billfishes is characterized by an extended rostrum or ‘bill’.
* While various functions (e.g. foraging and hydrodynamic benefits) have been proposed for this structure, until now no study has directly investigated the mechanisms by which billfishes use their rostrum to feed on prey.
* The first unequivocal evidence of how the bill is used by Atlantic sailfish (Istiophorus albicans) to attack schooling sardines in the open ocean is presented.
* Using high-speed video-analysis, it is shown that (i) sailfish manage to insert their bill into sardine schools without eliciting an evasive response and (ii) subsequently use their bill to either tap on individual prey targets or to slash through the school with powerful lateral motions characterized by one of the highest accelerations ever recorded in an aquatic vertebrate.
* The results demonstrate that the combination of stealth and rapid motion make the sailfish bill an extremely effective feeding adaptation for capturing schooling prey.
Sailfish Hunting Sardines (Normal & Slow Motion Attacks) (http://www.youtube.com/watch?v=VISEHbpHkn4#)
PDF available.
Reference:
Domenici, P. et al. (2014). How sailfish use their bills to capture schooling prey. Proceedings of the Royal Society B, 281: 20140444.
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Awesome footage!
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The dilema of derelict gear
* Every year, millions of pots and traps are lost in crustacean fisheries around the world. Derelict fishing gear has been found to produce several harmful environmental and ecological effects, however socioeconomic consequences have been investigated less frequently.
* The economic effects of a substantial derelict pot removal program in the largest estuary of the United States, the Chesapeake Bay were analyzed.
* By combining spatially resolved data on derelict pot removals with commercial blue crab (Callinectes sapidus) harvests and effort, it is shown that removing 34,408 derelict pots led to significant gains in gear efficiency and an additional 13,504 MT in harvest valued at US $21.3 million—a 27% increase above that which would have occurred without removals.
* Model results are extended to a global analysis where it is seen that US $831 million in landings could be recovered annually by removing less than 10% of the derelict pots and traps from major crustacean fisheries.
* An unfortunate common pool externality, the degradation of marine environments is detrimental not only to marine organisms and biota, but also to those individuals and communities whose livelihoods and culture depend on profitable and sustainable marine resource use.
PDF available.
Reference:
Scheld, A. M., D. M. Bilkovic & K. J. Havens (2016). The dilemma of derelict gear. Scientific Reports, 6: 19671.
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Great footage John explains the bill rash we so like to see on our lures :-)
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DNA evidence shows that hatcheries cause substantial, rapid genetic changes
The research, published today in Nature Communications, found that after one generation of hatchery culture, the offspring of wild fish and first-generation hatchery fish differed in the activity of more than 700 genes.
A single generation of adaptation to the hatchery resulted in observable changes at the DNA level that were passed on to offspring, scientists reported.
This research was conducted at Oregon State University in collaboration with the Oregon Department of Fisheries and Wildlife.
Scientists say the findings essentially close the case on whether or not wild and hatchery fish can be genetically different.
Source:
http://www.eurekalert.org/pub_releases/2016-02/osu-des021216.php (http://www.eurekalert.org/pub_releases/2016-02/osu-des021216.php)
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Challenges of estimating post-release mortality of istiophorid billfishes caught in the recreational fishery: A review
* Istiophorid billfishes are targeted in recreational fisheries throughout the tropical and subtropical waters of the world's oceans.
* Over the past thirty years, changes in management regulations and increased angler conservation awareness have resulted in an increasing proportion of the billfish catch being released alive, and in many areas the fishery is principally catch-and-release.
* However, the fate of released fish, and thus the fishing mortality associated with the recreational fishery, is not well understood.
* Some insights into post-release mortality of billfishes caught in the recreational fishery have been gained from analyses of conventional tag data, hooking location information, and acoustic tracking data.
* Over the past 10 years pop-up satellite archival tags (PSATs) have been used to specifically estimate post-release mortality for a limited number billfish species.
* Extrapolation of the results of these limited studies throughout the various recreational billfish fisheries is not prudent due to potential influences of different species, areas, seasons, fishing styles, and hook types.
* The current high cost of PSATs presents a significant obstacle to evaluating the effect of these variables on rates of post-release survival. Nonetheless, the results of the few studies to date have had an important impact on fisheries management and the behavior of recreational anglers.
PDF available.
Reference:
Graves, J. E. & A. Z. Horodysky (2015). Challenges of estimating post-release mortality of istiophorid billfishes caught in the recreational fishery: A review. Fisheries Research, 166: 163-168.
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Postrelease mortality in istiophorid billfish
* Meta-analysis (inverse-variance, random-effects model) involving 46 studies was used to estimate the effect size of postrelease mortality (Fr) in six istiophorid billfish species (black marlin (Istiompax indica), blue marlin (Makaira nigricans), longbill spearfish (Tetrapturus pfluegeri), sailfish (Istiophorus platypterus), striped marlin (Kajikia audax), and white marlin (Kajikia albida) following release from recreational, longline, and harpoon fishing gears.
* The studies involved 400 reporting pop-up satellite archival tags and 64 reporting acoustic (ultrasonic) tags.
* Despite fish being captured, tagged, and released under widely disparate conditions, locations, and gear types, Fr was homogeneous among species.
* Variability in Fr was principally due to random sampling error within studies with no evident patterns.
* Fifteen studies (33% of tags) indicated no mortality, and the overall summary effect size for Fr was 13.5% (95% CI: 10.3%–17.6%).
* Since the random-effects model decomposed to a fixed-effect model when the between-studies variance T2 = 0.00, results were confirmed using exact nonparametric inferential tests and sensitivity analyses.
* The results support earlier findings in the Atlantic and substantiate the majority of istiophorid billfish survive when released from recreational and longline fishing gear, clearly implying catch-and-release as a viable management option that permits fishing activity while protecting parental biomass and the fishery.
PDF available.
Reference:
Musyl, M. K., C. D. Moyes, R. W. Brill, B. L. Mourato, A. West, L. M. McNaughton, W.-C. Chiang & C.-L. Sun (2015). Postrelease mortality in istiophorid billfish. Canadian Journal of Fisheries and Aquatic Sciences, 72: 538-556.
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Postrelease mortality in istiophorid billfish
* The results support earlier findings in the Atlantic and substantiate the majority of istiophorid billfish survive when released from recreational and longline fishing gear, clearly implying catch-and-release as a viable management option that permits fishing activity while protecting parental biomass and the fishery.
That's brilliant news! Finally we can put an end to the nonsense and speculation.
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To be honest ive never understood the discussion... If released and floating away belly up and a 0.005% chance of survival, it's still 100% higher survival possibility than on the deck. The amount of fish caught with entire gill plates or jaws missing should have been enough evidence years ago.
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Awesome news indeed.
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Growth rate of speckled snapper Lutjanus rivulatus (Teleostei: Lutjanidae) based on tag-recapture data from the iSimangaliso Wetland Park, South Africa
* The growth rate of speckled snapper Lutjanus rivulatus was investigated using data from a long-term tag-recapture study conducted in the St Lucia Marine Reserve within the iSimangaliso Wetland Park, a World Heritage Site in northern KwaZulu-Natal, South Africa;
* A total of 1 429 L. rivulatus were tagged and 453 (31.7%) individual fish were recaptured one or more times;
* Growth rates were modelled from the tag-recapture data using a maximum-likelihood approach;
* It is shown that L. rivulatus is a slow-growing species with L∞ = 918 mm FL, K = 0.06 and phi-prime (Ø, the
growth index) = 2.69;
* The effects of deep-hooking and multiple captures were tested and this revealed that there was no significant impact on the growth of L. rivulatus;
* The growth index was lower than that recorded in many other similar congeneric species;
* Slow growth, coupled with high levels of residency and site fidelity, suggest that this species is vulnerable to exploitation and that a precautionary approach towards future management is appropriate.
PDF available.
Reference:
Mann, B. Q., B. Lee & P. D. Cowley (2016). Growth rate of speckled snapper Lutjanus rivulatus (Teleostei: Lutjanidae) based on tag-recapture data from the iSimangaliso Wetland Park, South Africa. African Journal of Marine Science, 38: 111-118.
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Over 30% recapture rate is quite amazing. Just shows how extremely territorial they are.
Release your Speckleds!
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Knew I'd get your attention Reefz!
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Very slow growing... So how old would this one be?! :shk
(http://www.ultimateangling.co.za/index.php?action=dlattach;topic=20030.0;attach=133544;image)
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According to Mann et al. (2016) this species grows about 35 mm/year. So that fish in the pic (assuming it was 25 cm long), would be roughly 7 years old.
And it would actually be a teenager!!!! It grows to 80 cm and about 12 kg!!!!
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Pffft 25cm.
It was 63cm long... <:
:rotfl
18 or so years... thank goodness I put it back :shk
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Thats an old fish!
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Pffft 25cm.
It was 63cm long... <:
:rotfl
18 or so years... thank goodness I put it back :shk
oops sorry!!! in my defense, that tape must be in inches :blush:
That was a great catch!
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Thats an old fish!
[/quote] walkerskiller
:lolo: even older tape :hehe: :toppie: :toppie:
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Plastic ingestion by estuarine mullet Mugil cephalus (Mugilidae) in an urban harbour, KwaZulu-Natal, South Africa
* Coastal urban environments have high plastic pollution levels, and hence interactions between plastic debris and marine life are frequent;
* Plastic ingestion by mullet Mugil cephalus in Durban Harbour, KwaZulu-Natal, South Africa is reported;
* Of 70 mullet (13.0–19.5 cm total length), 73% had plastic particles in their guts, with a mean of 3.8 particles per fish (SD 4.7);
* Plastic ingestion showed no relation to digestive tract content or fish length;
* White and clear plastic fibres were ingested most commonly;
* This urban population of M. cephalus had a higher incidence of plastic ingestion than has been reported in studies on fish from other coastal areas or the oceanic environment.
PDF available.
Reference:
Naidoo, T., A.J. Smit & D. Glassom (2016).Plastic ingestion by estuarine mullet Mugil cephalus (Mugilidae) in an urban harbour, KwaZulu-Natal, South Africa. African Journal of Marine Science, 38: 145-149.
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The ecological role of sharks on coral reefs
* Sharks are considered the apex predator of coral reefs, but the consequences of their global depletion are uncertain;
* The ecological roles of sharks on coral reefs and, conversely, the importance of reefs for sharks is explored;
* It was found that most reef-associated shark species do not act as apex predators but instead function as mesopredators along with a diverse group of reef fish;
* While sharks perform important direct and indirect ecological roles, the evidence to support hypothesised shark-driven trophic cascades that benefit corals is weak and equivocal;
* Coral reefs provide some functional benefits to sharks, but sharks do not appear to favour healthier reef environments;
* Restoring populations of sharks is important and can yet deliver ecological surprise.
PDF available.
Reference
Roff, G., C. Doropoulos, A. Rogers, Y.-M. Bozec, N. C. Krueck, E. Aurellado, M. Priest, C. Birrell & P. J. Mumby (2016). The ecological role of sharks on coral reefs. Trends in Ecology and Evolution, 31: 395-407.
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Very, very interesting...
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Coral-reef finfish species disappearances in global epicentre of marine shorefish diversity
* In the Philippines, very high fishing pressure coincides with the globally greatest number of shorefish species, yet no long-term fisheries data are available to explore species-level changes that may have occurred widely in the most species rich and vulnerable marine ecosystem, namely coral reefs;
* Through 2655 face-to-face interviews conducted between August 2012 and July 2014, tchê authors used fishers’ recall of past catch rates of reef-associated finfish to infer species disappearances from catches in five marine key biodiversity areas (Lanuza Bay, Danajon Bank, Verde Island Passage, Polillo Islands and Honda Bay);
* They modeled temporal trends in perceived catch per unit effort (CPUE) based on fishers’ reports of typical good days’ catches using Generalized Linear Mixed Modelling;
* Fifty-nine different finfish disappeared from catches between the 1950s and 2014; 42 fish were identified to species level, two to genus, seven to family and eight to local name only;
* Five species occurring at all sites with the greatest number of fishers reporting zero catches were the green bumphead parrotfish (Bolbometopon muricatum), humphead wrasse (Cheilinus undulatus), African pompano (Alectis ciliaris), giant grouper (Epinephelus lanceolatus) and mangrove red snapper (Lutjanus argentimaculatus);
* Between the 1950s and 2014, the mean perceived CPUE of bumphead parrotfish declined by 88%, that of humphead wrasse by 82%, African pompano by 66%, giant grouper by 74% and mangrove red snapper by 64%;
* These declines were mainly associated with excess and uncontrolled fishing, fish life-history traits like maximum body size and socio-economic factors like access to market infrastructure and services, and overpopulation;
* The fishers’ knowledge is indicative of extirpations where evidence for these losses was otherwise lacking;
* The models provide information as basis for area-based conservation and regional resource management particularly for the more vulnerable, once common, large, yet wide-ranging reef finfish species.
PDF available.
Reference:
Lavides, M.N., E.P. V. Molina , G.E. de la Rosa Jr., A.C. Mill , S.P. Rushton, S.M. Stead & N.V.C. Polunin (2016). Patterns of coral-reef finfish species disappearances inferred from fishers’ knowledge in global epicentre of marine shorefish diversity. PLoS ONE 11(5): e0155752.
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Nine decades of fish movement research in southern Africa: A synthesis of research and findings from 1928 to 2014
* Unprecedented concern over the biological effects of over-exploitation, together with rapid technological advances in biotelemetry, have provided
the impetus for much research, on a global scale, into the movement of marine animals.
* The authors reviewed 101 marine and estuarine fish movement studies from southern Africa, published from 1928 to 2014, with the aim of synthesising research trends and findings.
* Trends showed an increasing emphasis on fish movement research in publications in the sub-tropical and warm-temperate biogeographic regions along the south and east coasts of southern Africa.
* Although 63% of publications featured only marine studies, research into fine-scale habitat use in estuaries has been on the increase, concomitant with increasing accessibility of biotelemetry.
* Overall, 26 families were identified in the surveyed literature with regionally endemic sparids featuring in 32% of the publications.
* Ten movement themes were identified in the surveyed literature, including broad-scale movement patterns, which featured in 68% of studies, followed by fine-scale habitat usage (33%) and protected areas (26%).
* The most prominent phenomenon, emerging from this research, is that of partial migration, which describes the occurrence of resident and migratory behaviour within a coexisting animal population.
* Substantial progress has also been made in unravelling the complexities of fine-scale habitat usage in marine reserves and in estuaries.
* While this knowledge has enabled more effective management of South Africa’s multi-user, multi-species fisheries, focus should now be directed at improving our understanding of the commonalities in movement behaviour, the associated driving forces behind this behaviour and the nature of movement across reserve boundaries.
PDF available.
Reference:
Maggs, J. Q. & P. D. Cowley (2016). Nine decades of fish movement research in southern Africa: A synthesis of research and findings from 1928 to 2014. Reviews in Fish Biology and Fisheries, DOI 10.1007/s11160-016-9425-2.
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Impacts of plastic ingestion on post-hatchling loggerhead turtles off South Africa
* Twenty-four of 40 (60%) loggerhead turtle Caretta caretta post-hatchlings (carapace < 9 cm) that died within 2 months of stranding on southern Cape beaches in April 2015 contained ingested anthropogenic debris;
* Plastic comprised of 99% of debris: 77% hard plastic fragments, 10% flexible packaging and 8% fibres; industrial pellets comprised only 3%, compared to ~ 70% in 1968–1973, when 12% of stranded post-hatchlings contained plastics;
* Turtles selected for white (38%) and blue (19%) items, but translucent items (23%) were under-represented compared to beach mesodebris;
* Ingested loads did not decrease up to 52 days in captivity, indicating long retention times;
* Plastic killed 11 turtles by blocking their digestive tracts or bladders, and contributed to the deaths of five other turtles;
* Our results indicate that the amount and diversity of plastic ingested by post-hatchling loggerhead turtles off South Africa have increased over the last four decades, and now kill some turtles.
PDF available.
Reference:
Ryan, P. G., G. Cole, K. Spiby, R. Nel, A. Osborne & V. Perold (2016). Impacts of plastic ingestion on post-hatchling loggerhead turtles off South Africa. Marine Pollution Bulletin, 107: 155-160.
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Didn't like the last one. :-( Makes me sick :puke:
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Yeah humans are not giving them much room to thrive .... eat the adults, poison the babies, eish...
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Extremely interesting and insightful bru :win:
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Physiological response of the Orange-Vaal smallmouth yellowfish Labeobarbus aeneus, to catch-and-release angling
* The practice of catch-and-release fishing has been widely promoted by angling fraternities as a fisheries management tool;
* The aim of this investigation was to determine the physiological response of Orange-Vaal smallmouth yellowfish, Labeobarbus aeneus, to catch-and-release angling in the Vaal River, South Africa;
* Fish were collected using standard fly-fishing techniques, anaesthetised in clove oil and blood was drawn from the caudal vein; thereafter the fish were weighed, measured, revived and released;
* Blood plasma was analysed for concentrations of glucose, cortisol and lactate to determine the effects of angling duration, fish size and water temperature;
* Larger fish were angled for a longer duration compared with smaller fish;
* Levels of glucose were affected by water temperature (influenced by time of year);
* Plasma glucose concentrations decreased with greater angling duration;
* Few individuals (n = 12) showed increased plasma cortisol concentrations;
* In extended-capture fish (angled for >1 min), lactate concentrations increased significantly above values for rapid-capture fish (angled for >30 s);
* These data suggest that catch-and-release causes physiological stress to fish, but nonetheless this practice can be a valuable fisheries management tool to ensure the sustainability of fish populations;
* Other factors beyond the ‘angling’ time are likely to contribute to physiological disruptions in homeostasis and therefore handling and air exposure of angled fish should be included in future catch-and-release angling studies;
* In addition, the longer-term impact of angling on fish health should also be determined.
Reference:
Smit, N.J., R. Gerber, R. Greenfield & G. Howatson (2016). Physiological response of one of South Africa’s premier freshwater sport angling species, the Orange-Vaal smallmouth yellowfish Labeobarbus aeneus, to catch-and-release angling. African Zoology, 51: 61-67.
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Very interesting Marcos :win: :yellow:
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An integrated mark-recapture and genetic approach to estimate the population size of white sharks in South Africa
* The loss of apex marine predators has been reported to have a cascade of detrimental effects on marine ecosystems; however, the general lack of empirical data can severely limit our understanding of the ecological interactions among marine species;
* In this study an integrated approach using mark-recapture and genetic techniques to assess population estimates of white sharks Carcharodon carcharias is proposed;
* Between 2009 and 2011, 4389 dorsal fin photographic identifications were collected in Gansbaai, South Africa, from 426 white sharks and used in mark-recapture analyses;
* Saturation of new sightings occurred once 400 individuals were catalogued and the open population model POPAN suggested ranges between 353 and 522 individuals (95% confidence) and a point estimate of N = 438;
* Between 2010 and 2013, 302 biopsy samples were collected from 233 white sharks and used for a comparative genetic population estimate;
* Analyses of 14 microsatellite markers revealed a contemporary effective population size (CNe) of 333 individuals (95% CI = 247−487, pcrit = 0.02);
* These values were at least 52% less than those estimated in previous mark-recapture studies;
* Using this combination of techniques, a Ne:N ratio of 0.76 for white sharks is proposed, which advances our ability to accurately make inferences on elasmobranch population numbers in general;
* Given the low population numbers of white sharks along the South African coastline, a negative effect on the ecological stability of the marine environment in this region is predicted.
pdf available.
Reference:
Andreotti, S., M. Rutzen, S. van der Walt, S. von der Heyden, R. Henriques, M. Meÿer, H. Oosthuizen & C. A. Matthee (2016). An integrated mark-recapture and genetic approach to estimate the population size of white sharks in South Africa. Marine Ecology Progress Series, 552: 241-253.
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Very interesting...
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That last GW study has been pretty harshly criticized by other researchers....
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That last GW study has been pretty harshly criticized by other researchers....
Wonder what sort of criticism... can you provide some links or other details Marthin? The Andreotii et al. paper was published on 23 June...
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https://www.facebook.com/meaghen.m.gray/posts/10157218581875788?comment_id=10157218816875788 (https://www.facebook.com/meaghen.m.gray/posts/10157218581875788?comment_id=10157218816875788)
Some of the discussions....
More of a discussion however its a bit more severe behind the scenes... from what i gathered, the researchers pushed to publish, very poor if any reviews by peers, and complete ignorance of previous studies or methodology. I'm by no means a scientists more of a reader....
My comments on the matter are based on general fisheries research where the outcome is decided prior to the research started, in other words the research is done in a way and results "manipulated" to arrive at a predetermined result. Not necessarily in this instance but others.
Then from a general point of view.... our coastline is 2700km. If you deduct the 700 km from Cape Town to Alexanderbay where they don't generally appear, leaves you with 2000 from Cape Town to Moz. and let's say the study is correct, with max 500 gw adults... That leaves you with just 4km of coast per apex predator. (and i do believe there are quite a few more and many more sub adults that don't gongregate around gansbaai.)
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Very, very interesting!
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Thanks Marthin!
Eish... the politics behind science.... this was part of a PhD project.... so there's always a bit of a time issue there... oh well...
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Persistent organic pollutants in albacore tuna (Thunnus alalunga) from Reunion Island (Southwest Indian Ocean) and South Africa in relation to biological and trophic characteristics
* The contamination of albacore tuna (Thunnus alalunga) by Persistent Organic Pollutants (POPs), namely polychlorinated biphenyls (PCBs) and dichlorodiphenyl-trichloroethane (DDT), was investigated in individuals collected from Reunion Island (RI) and South Africa's (SA) southern coastlines in 2013, in relation to biological parameters and feeding ecology;
* The results showed lower PCB and DDT concentrations than those previously reported in various tuna species worldwide;
* A predominance of DDTs over PCBs was revealed, reflecting continuing inputs of DDT;
* Tuna collected from SA exhibited higher contamination levels than those from RI, related to higher dietary inputs and higher total lipid content;
* Greater variability in contamination levels and profiles was identified in tuna from RI, explained by a higher diversity of prey and more individualistic foraging behaviour;
* PCB and DDT contamination levels and profiles varied significantly in tuna from the two investigated areas, probably reflecting exposure to
different sources of contamination.
pdf available.
Reference:
Munschy, C., N. Bodin, M. Potier, K. Héas-Moisan, C. Pollono, M. Degroote, W. West, S. J. Hollanda, A. Puech, J. Bourjea & N. Nikoli
(2016). Persistent organic pollutants in albacore tuna (Thunnus alalunga) from Reunion Island (Southwest Indian Ocean) and South Africa in relation to biological and trophic characteristics. Environmental Research, 148: 196-206.
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Effect of angling intensity on feeding behaviour and community structure of subtropical reef-associated fishes
* Baited hooks used in angling may influence foraging behaviour and trophic interactions among reef fishes, which may be reinforced over successive generations;
* In contrast to other scavenging opportunities involving pulsed resources (e.g. food falls), there is an asymmetric susceptibility to becoming hooked for species and size classes;
* The resulting effect may provoke behavioural changes in reef fishes through cognitive or phenotypic selective processes;
* The effects of angling pressure on the feeding behaviour and community structure of reef-associated fishes using a novel underwater video approach was investigated;
* Fish community and behavioural responses to simulated angling baits were assessed at paired sites of contrasting angling pressure at Amity Point and Ballina, on the east coast of Australia from late 2013 to 2014;
* Bait introduction differentially influenced trophic interactions of reef-associated communities according to angling intensity regime;
* Locations with higher angling pressure correlated with increased feeding hesitation among potentially capture-susceptible species, most notably Acanthopagrus australis;
* The feeding hierarchy of less dominant feeders and their interactions also differed compared with those exhibited under lower angling intensity regimes;
* Specifically, smaller opportunistic feeders (e.g. Microcanthus strigatus) that could utilise angling bait for dietary supplementation without risk of being hooked were able to maintain higher feeding ranks in areas subject to high angling pressure due to reduced interference competition from larger species, e.g. A. australis;
* The potential for complex ecological effects to follow from high-intensity angling activities is discussed and the potentially confounding effects of using bait as a focus for fish assemblage monitoring highlighted.
pdf available.
Reference:
Colefax, AP, MDE Haywood & IR Tibbetts (2016). Effect of angling intensity on feeding behaviour and community structure of subtropical reef-associated fishes. Marine Biology 163: 85. doi:10.1007/s00227-016-2857-3.
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So some Bream species become hesitant about feeding on baited hooks?! Learned response? :shk
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Crazy to think what us humans are capable of and worst is that we might never even realise the effects of our behaviour!
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Something to think about, over how long a period was this particular study done? Reason for asking relates to seasonal baits/food.
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Thats crazy stuff, wow!
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Something to think about, over how long a period was this particular study done? Reason for asking relates to seasonal baits/food.
According to the paper, the survey took place from late December 2013 through to the beginning of March 2014.
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Thanx for the reply, I was just wondering what influence seasonal availability of a certain food source would've had on the study?
Would've been interesting had they conducted it over a two year period, I know funding might have been a serious issue, nonetheless if they could perhaps they might have stumbled upon a repeat of a pattern. Not sure just a thought?
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Monitoring the recovery of a previously exploited surf-zone fish community in the St Lucia Marine Reserve, South Africa, using a no-take sanctuary area as a benchmark
* Limiting accessibility to a fishing area can reduce fishing effort effectively and may therefore promote local recovery of depleted stocks. In January 2002, beach driving was banned in South Africa, thereby reducing angler access to large areas of the coastline, particularly in less-developed areas;
* In November 2001 a project had been established in the St Lucia Marine Reserve, on the east coast of South Africa, to compare surf-zone fish populations inside a no-take sanctuary zone with those in an adjacent exploited area;
* Subsequent to the ban, the aim of the project was adapted such that surf-zone fish populations were monitored for potential recovery in what had been the exploited area, located to the north of Cape Vidal, which anglers could no longer access easily, because of the
prohibition on beach driving;
* Standardised research fishing was conducted at two sites in the previously exploited area and two sites in the no-take sanctuary;
* Conventional stock-status indicators showed evidence of recovery in the four most common species caught in the previously exploited area, in terms of both abundance and biomass;
* Generalised additive mixed models were used to account for the influence of targeting specific species; however, subtle differences in habitat between the sampling sites, improved angling skill over time, variability in recruitment, and differential species-specific responses complicated interpretation of results;
* The implications of the findings are discussed in terms of the future monitoring and management of marine protected areas both within the St Lucia
Marine Reserve and farther afield.
pdf available.
Reference:
Mann, BQ, H Winker, JQ Maggs & SN Porter (2016). Monitoring the recovery of a previously exploited surf-zone fish community in the St Lucia Marine Reserve, South Africa, using a no-take sanctuary area as a benchmark. African Journal of Marine Science, 38(3): 423-441.
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Life cycle of chokka-squid Loligo reynaudii in South African waters
* This short note summarises past and current knowledge of the life cycle of chokka-squid Loligo reynaudii d’Orbigny, 1845, in South African waters;
* Prior to approximately 2010, the chokka-squid stock was considered simple and uniform, with one paralarval pool, the drift of paralarvae westwards, one main nursery area and one main, long spawning migration of adult squid eastwards, back to the main spawning grounds;
* Based on new information, this life-history scheme has been revised. Genetically, the stock is uniform; however, morphologically, it comprises three main geographic groups;
* It is proposed that the differences between the groups originate from many different paralarval events and that short (not long) migrations dominate the life cycle.
PDF available.
Reference:
Lipiński, M.R., J.S.F. van der Vyver, P. Shaw & W.H.H. Sauer (2016). Life cycle of chokka-squid Loligo reynaudii in South African waters. African Journal of Marine Science 2016, 38(4): 589-593.
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Seasonally and spatially referenced estimates of recreational shore-angling effort, catch composition, catch rates and total catch in the Goukamma Marine Protected Area, South Africa
* A roving creel survey of the recreational shore fishery along the 16.4-km coastline in the Goukamma Marine
Protected Area on the south coast of South Africa was conducted from 2009 to 2011;
* Some 838 patrols were stratified equally among months, areas and years, but intentionally biased towards weekends;
* Angler densities at Buffalo Bay and Groenvlei were 0.59 and 0.28 anglers km−1, respectively;
* Weekend densities were double to quadruple weekday densities and fishing during winter was more popular than during summer;
* Area, habitat and distance to access points explained variation in angler densities;
* Shannon–Wiener diversity in catches declined from 2.18 in an earlier (1993–2002) survey to 1.79;
* Although the order of species abundance in the catches remained largely unchanged, blacktail Diplodus capensis dominance increased to 57.3% by number, at the expense of galjoen Dichistius capensis;
* Habitat explained 27% of the variance in catch composition;
* The catch per unit effort (CPUE) for the top nine species ranged from 0.19 to 6.35 fish 100-h−1.
* The CPUE of all species, except spotted grunter Pomadasys commersonnii, declined;
* Blacktail and galjoen CPUE declined by 17% and 77%, respectively;
* The total catch estimate was 2 986 fish y−1;
* Transgressions of size limits were common;
* The results suggest that the fishery is overexploited and that catch rates are declining.
pdf available.
Reference:
Attwood, C. G., C. S. van Zyl, A. T. Lombard & C. McCagh (2016). Seasonally and spatially referenced estimates of recreational shore-angling effort, catch composition, catch rates and total catch in the Goukamma Marine Protected Area, South Africa. African Journal of Marine Science. 38 (4): 563-579.
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Assessing trophic adaptability is critical for understanding the response of predatory fishes to climate change: a case study of Pomatomus saltatrix in a global hotspot
* There is a growing need to incorporate biotic interactions, particularly those between predators and their prey, when predicting climate-driven shifts in marine fishes.
* Predators dependent on a narrow range of prey species should respond rapidly to shifts in the distribution of their prey, whereas those with broad trophic adaptability may respond to shifts in their prey by altering their diet.
* Small pelagic fishes are an extremely important component of the diet of many marine predators. However, their populations are expected to shift in distribution and fluctuate in abundance as the climate changes.
* A comparative study of the seasonal diet of adult Pomatomus saltatrix over two periods (June–December 2006 and 2012) was conducted and examined the available data on small pelagic fishes biomass in a global hotspot (the coastal region of southern Angola, southern Africa) to gain an understanding of the tropic adaptability of the species.
* Despite a drop (630 000 t to 353 000 t) in the abundance of their dominant prey (Sardinella aurita) in the region, it remained the most important prey item during both study periods (Period 1 = 99.3% RI, Period 2 = 85.3% RI, where %RI is a ranking index of relative importance).
* However, the diet during Period 2 was supplemented with prey typically associated with the nearshore zone.
* The seasonal data showed that P. saltatrix were capable not only of switching their diet from S. aurita to other prey items, but also of switching
their trophic habitat from the pelagic to the nearshore zone.
* These findings suggest that P. saltatrix will not necessarily co-migrate if there is a climate-driven shift in the distribution of small pelagic fishes (their dominant prey).
* Accordingly, understanding the trophic adaptability of predators is critical for understanding their response to the impacts of climate change.
pdf available.
Reference:
Potts, W. M., R. S. J. Bealey & A.-R. Childs (2016). Assessing trophic adaptability is critical for understanding the response of predatory fishes to climate change: a case study of Pomatomus saltatrix in a global hotspot. African Journal of Marine Science, 38 (4): 539–547.
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Very interesting Marcos.
Do you know what the status of the Chokka stocks are in SA by any chance? Normally see a lot of Chokka boats in the EC in December and havent seen any in 2 years.
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Very interesting Marcos.
Do you know what the status of the Chokka stocks are in SA by any chance? Normally see a lot of Chokka boats in the EC in December and havent seen any in 2 years.
According to a report published by the Department of Agriculture, Forestry and Fisheries (Prochazka et all., 2014 - STATUS OF THE SOUTH AFRICAN MARINE FISHERY RESOURCES 2014): "Updated analyses suggest that the squid resource is less productive than previously thought. Declines in the stock have been detected, necessitating a reduction in fishing effort."
Not sure if a new assessment has been conducted.
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Always interesting Marcos, thanks for sharing! :+ cred:
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Cool thanks Marcos, :+ cred:
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Why have global shark and ray landings declined: improved management or overfishing?
* Global chondrichthyan (shark, ray, skate and chimaera) landings, reported to the United Nations Food and Agriculture Organization (FAO), peaked in 2003 and in the decade since have declined by almost 20%;
* In the FAO’s 2012 ‘State of the World’s Fisheries and Aquaculture’ report, the authors ‘hoped’ the reductions in landings were partially due to management implementation rather than population decline;
* This study tested this hypothesis;
* Post-peak chondrichthyan landings trajectories from 126 countries were modelled against seven indirect and direct fishing pressure measures and eleven measures of fisheries management performance, while accounting for ecosystem attributes;
* It was found that the recent improvement in international or national fisheries management was not yet strong enough toaccount for the recent decline in chondrichthyan landings;
* Instead, the landings declines were more closely related to fishing pressure and ecosystem attribute measures;
* Countries with the greatest declines had high human coastal population sizes or high shark and ray meat exports such as Pakistan, Sri Lanka and Thailand;
* While important progress had been made, country-level fisheries management measures did not yet have the strength or coverage to halt overfishing and avert population declines of chondrichthyans;
* Increased implementation of legally binding operational fisheries management and species-specific reporting is urgently required to avoid declines and ensure fisheries sustainability and food security.
pdf available.
Reference
Davidson, L. N. K., M. A. Krawchuk & N. K. Dulvy (2016). Why have global shark and ray landings declined: improved management or overfishing? Fish and Fisheries, 17: 438-458.
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Assessing a social norms approach for improving recreational fisheries compliance
* This study aimed to assess the suitability of the Berkowitz’ (2005) social norms approach (SNA) for improving compliance behaviour amongst recreational fishers.
* A total of 138 recreational shore anglers were interviewed in Eastern Cape, South Africa and asked about their compliance, attitudes towards compliance, perceptions of compliance and the attitudes of other anglers.
* Results indicate that angler compliance for individual regulations was relatively high (75%–90%).
* Attitudes of anglers towards compliance was positive, with >80% feeling that “breaking any regulation is wrong.”
* Yet, as predicted by the SNA, interviewees often overestimated the non- compliance and negative attitudes of other anglers, particularly as their social proximity decreased.
* Interviewees with the greatest misperceptions were also less compliant.
* The social norms present in the Eastern Cape rock and surf fishery fulfil the criteria required for the application of the SNA, suggesting that this approach may provide a suitable normative intervention for improving compliance to be used in conjunction with instrumental approaches in recreational fisheries.
PDF available.
Reference:
Bova, C. S., S. J. Halse, S. Aswani & W. M. Potts (2017). Assessing a social norms approach for improving recreational fisheries compliance. Fisheries Management and Ecology, 24: 117-125.
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Satellite snafu masked true sea-level rise for decades
http://www.nature.com/news/satellite-snafu-masked-true-sea-level-rise-for-decades-1.22312?WT.ec_id=NATURE-20170720&spMailingID=54526224&spUserID=MjA1NTA3MjA0OQS2&spJobID=1203043033&spReportId=MTIwMzA0MzAzMwS2 (http://www.nature.com/news/satellite-snafu-masked-true-sea-level-rise-for-decades-1.22312?WT.ec_id=NATURE-20170720&spMailingID=54526224&spUserID=MjA1NTA3MjA0OQS2&spJobID=1203043033&spReportId=MTIwMzA0MzAzMwS2)
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:tkx: John for another :win: report , always interesting, :toppie:
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:tkx: John for another :win: report , always interesting, :toppie:
Thanks. Glad somebody actually reads these :hehe:
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:tkx: John for another :win: report , always interesting, :toppie:
Thanks. Glad somebody actually reads these :hehe:
Always! Love them. Very interesting.
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Ud be amazed how many of us read it...
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Genetic stock structure of white steenbras Lithognathus lithognathus (Cuvier, 1829), an overexploited fishery species in South African waters
* White steenbras Lithognathus lithognathus (Teleostei: Sparidae) is an overexploited marine fish species endemic to South Africa.
* Overexploitation in recreational, subsistence and commercial fisheries has resulted in stock collapse and the need for improved management of the species.
* Adults are thought to undertake large-scale annual spawning migrations, yet studies of their movement indicate low levels of connectivity among coastal regions.
* To address this, mitochondrial DNA sequencing and genotyping of microsatellite loci in the nuclear genome were conducted to determine the genetic stock structure and level of gene flow in this species.
* Genetic diversity was high throughout the species’ core distribution, with no evidence of isolation by way of distance or localised spawning.
* Low, non-significant pairwise fixation indices (FST, RST and Jost’s Dest) indicated low genetic differentiation and high levels of gene flow.
* The observed results, and agreement between mitochondrial and microsatellite DNA, confirm that white steenbras exists as a single genetic stock with high levels of gene flow throughout its distribution.
pdf available.
Reference:
Bennett, R. H., K. Reid, G. Gouws, P. Bloomer & P. D. Cowley (2017). Genetic stock structure of white steenbras Lithognathus lithognathus (Cuvier, 1829), an overexploited fishery species in South African waters. African Journal of Marine Science, 39: 27-41.
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John can u give me the English for that please. I love the steenies but what are they saying. Do they migrate to spawn or are local poor estuaries to blame.
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John can u give me the English for that please. I love the steenies but what are they saying. Do they migrate to spawn or are local poor estuaries to blame.
Marthin you putting me between a sword and a hard place :hehe: will try my best
Here's a quick run down on the life history of the species (not according to the study I just posted, which basically says there's one single stock (genetically) along the coastaline. The info below was taken from Rhett Bennett's PhD thesis:
* Early juvenile white steenbras recruit into estuaries between about 18 and 50 mm TL. The size at recruitment tends to increase and the timing of recruitment occurs later in the year in estuaries further west along the coastline.
* Juveniles are dependent on estuaries for the first year after recruitment, until a size of about 150 mm TL, i.e. ± 130 mm FL;
* Fish larger than 130 mm FL are thought to leave estuarine nursery areas and move to subtidal marine habitats, where they inhabit shallow nearshore sandy and mixed sand and rock areas
* Late juveniles (< 500 mm FL) show high levels of residency within the surf zone, and exhibit a shallow inshore distribution (< 10m)
* Larger fish (500 – 600 mm FL) move to deeper areas and begin to undertake larger-scale coastal movements, although some individuals remain resident.
Hope it helps?!
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Fishing practices and representations of shark conservation issues among users of a land-based shark angling online forum
Study conducted in the US, with interesting results. Direct relevance to RSA and Moz!
From the Abstract:
* Recreational fisheries can play a significant role in the population dynamics of threatened fish species, but have received much less research and management attention than commercial fisheries.
* Land-based anglers are a group of recreational fishers that fish from beaches or piers; however, comparatively little is known about the practices and perceptions of this stakeholder group.
* In order to gather data for an initial assessment of the fishing practices of land-based anglers and their perspectives on shark conservation issues, a content and discourse analysis of an online discussion forum used by the largest land-based shark fishing club in Florida was performed.
* Discussion board content analysis can identify evidence that certain perceptions or practices exist within a studied sample, but cannot be used to estimate how common those perceptions and practices are among the wider population.
* Evidence was found that forum users are demographically distinct from other recreational anglers in Florida, and are mostly young males.
* Some forum users perceive themselves as relatively low-income compared with other fishing stakeholder groups.
* There was no evidence in forum discussions that patterns of reported landing and release of hammerhead and tiger sharks changed following the introduction of new legal protections for these species in 2012.
* This study identified a minimum of dozens of cases of illegal shark fishing practices among forum users, and found evidence that some users are aware that these practices are illegal.
* There was evidence that some users believe that their own practices have no effect on shark populations and should not be regulated.
* Additionally, this study found the existence of mixed attitudes and levels of trust towards scientific researchers and environmentalists.
Some bullet points from the lead author on the findings:
- Many (a minimum of 389) cases of illegal fishing for protected species, including cases where the anglers themselves knew it was illegal and discussed ways to avoid getting caught or ways to avoid getting in trouble if caught;
- The introduction of new laws requiring the release of hammerhead and tiger sharks in Florida had no effect on reported handling or release practices of shark anglers;
- Recreational shark anglers in Florida agree that shark populations have declined significantly, but believe that their own practices play no role in this and should not be regulated (i.e., there is a problem, but the problem is someone else, not me);
- Land-based anglers (those who fish from a beach or pier instead of a boat) had mixed attitudes towards science and scientists, supported restrictions on commercial fishing in the name of conservation, opposed any restrictions on their own activities, and had negative attitudes towards conservationists despite sharing similar goals;
- Land-based shark fishing has the potential to introduce much more stress to sharks as they are dragged over rough terrain while lacking the buoyant support of water, which means that even if sharks are released, they are less likely to survive if handled this way;
- Land based anglers self-identify as relatively young, male, and low-income compared to other angler groups, and perceive themselves as having little political power compared to other Florida stakeholders, potentially contributing to lack of buy-in to fishing regulations.
- For the last several years, more large (non-Dogfish) sharks in the United States have been killed by recreational anglers than by commercial fishermen
pdf available.
Reference:
Shiffman, D. S., C. Macdonald, H. Y. Ganz & N. Hammerschlag (2017). Fishing practices and representations of shark conservation issues among users of a land-based shark angling online forum. Fisheries Research, 196: 13-26.
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Philopatry and dispersal of juvenile leervis Lichia amia (Teleostei: Carangidae) tagged in a warm-temperate South African estuary
* Understanding and characterising movement and area-use patterns of fishes within estuaries, as well as understanding the degree of connectivity between estuaries and the marine environment, can provide important insights into a species’ ecology, which is fundamental for effective management and conservation.
* Mark-and-recapture data obtained from the 082 TAG FISH Project, a dart-tagging programme, were used to describe movement patterns of juvenile leervis Lichia amia in the permanently open Swartkops Estuary, South Africa, as well as the degree of connectivity with the adjacent marine environment.
* A total of 628 juvenile leervis were tagged from 2008 to 2015, of which 77 fish (12.3%) were recaptured, with juveniles comprising 85.7% of all measured recaptures.
* The majority of recaptures (75.3%) were made within the Swartkops Estuary, indicating estuarine philopatry, with 23.4% having moved less than 1 km, revealing site fidelity, but most (51.9%) displaying estuarine roaming.
* A smaller portion of recaptures (27.7%) had dispersed to other habitats; 16 (20.8%) displayed multiple habitat connectivity, while only 3 (3.9%) had undertaken long-distance movements (>100 km) and were recaptured up to 825 km northeast of the Swartkops Estuary.
* Lichia amia that had moved greater distances were characterised by a greater mean size and age at the time of recapture. This study provides valuable information on the philopatry and dispersal of juvenile L. amia.
pdf available.
Reference
Murray, T., P. Cowley, A.-R. Childs & R. Bennett (2017). Philopatry and dispersal of juvenile leervis Lichia amia (Teleostei: Carangidae) tagged in a warm-temperate South African estuary. African Journal of Marine Science, 39: 59-68.
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Estuarine and coastal connectivity of an estuarine-dependent fishery species, Pomadasys commersonnii (Haemulidae)
* Understanding the level of connectivity between estuarine and coastal waters is essential for appropriate management of estuarine-associated taxa.
* Most studies have focused on the role of a single estuary, while limited research exists on the importance of multiple estuaries to individuals of estuarine-associated species.
* This study used acoustic telemetry to assess the usage of multiple estuaries and coastal waters by the estuarine-dependent spotted grunter Pomadasys commersonnii.
* Twenty-six adult fish were tagged with acoustic transmitters in the Kariega and Bushmans estuaries, South Africa, and their movements along a 300-km stretch of Indian Ocean coastline were monitored for up to 17 months.
* Tagged individuals spent most of their time in the estuary where they were tagged (55% and 85% for fish tagged in the two estuaries, respectively), followed by time in the sea (30% and 15%) and in other estuaries (15% and <1%).
* The mean durations of sea trips for fish tagged in the Kariega Estuary or Bushmans Estuary, respectively, were 25 days (range 3–55) and 12 days (range 2–22).
* Of the fish that went to sea, 93% from the Kariega Estuary and 60% from the Bushmans Estuary visited other estuaries.
* Most visits were undertaken to the Swartkops, Bushmans and Kowie estuaries, although the longest durations were spent in the Sundays Estuary.
* Individuals moved to estuaries up to 130 km away. The total distance travelled between estuaries by an individual during the study was ~529 km, with means of 201 and 184 km, respectively, for fish tagged in the Kariega and Bushmans estuaries.
* Despite covering large distances between estuaries, individuals often returned to their tagging estuary.
* Residency in their tagging estuary, combined with frequent visits to a neighbouring estuary, highlights the importance of estuarine habitats for this popular fish species, even after reaching maturity.
pdf available.
Reference
Dames, M. H., P. D. Cowley, A.-R. Childs, R. H. Bennett, E. B. Thorstad & T. F. Næsje (2017). Estuarine and coastal connectivity of an estuarine-dependent fishery species, Pomadasys commersonnii (Haemulidae). African Journal of Marine Science, 39: 111-120.
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Fascinating that an adult Grunter travelled 529kms to visit another estuary!
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the longest durations were spent in the Sundays
I'd also like longer Sundays w;k
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the longest durations were spent in the Sundays
I'd also like longer Sundays w;k
:rotfl
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Global proliferation of cephalopods
* Human activities have substantially changed the world’s oceans in recent decades, altering marine food webs, habitats and biogeochemical processes;
* Cephalopods (squid, cuttlefish and octopuses) have a unique set of biological traits, including rapid growth, short lifespans and strong life-history plasticity, allowing them to adapt quickly to changing environmental conditions;
* There has been growing speculation that cephalopod populations are proliferating in response to a changing environment, a perception fuelled by increasing trends in cephalopod fisheries catch;
* To investigate long-term trends in cephalopod abundance, a global time-series of cephalopod catch rates (catch per unit of fishing or sampling effort) was assembled;
* It is shown that cephalopod populations have increased over the last six decades, a result that was remarkably consistent across a highly diverse set of cephalopod taxa;
* Positive trends were also evident for both fisheries-dependent and fisheries-independent time-series, suggesting that trends are not solely due to factors associated with developing fisheries;
* The results suggest that large-scale, directional processes, common to a range of coastal and oceanic environments, are responsible;
* This study presents the first evidence that cephalopod populations have increased globally, indicating that these ecologically and commercially important invertebrates may have benefited from a changing ocean environment.
pdf available.
Reference:
Doubleday, Z. A., et al. (2016). Global proliferation of cephalopods. Current Biology, 26: R406-R407.
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Is there also an increase in jellyfish? I've seen quite a bit of reference to it in the last few years.
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Is there also an increase in jellyfish? I've seen quite a bit of reference to it in the last few years.
Not really...
http://www.bbc.com/earth/story/20160905-are-swarms-of-jellyfish-taking-over-the-ocean (http://www.bbc.com/earth/story/20160905-are-swarms-of-jellyfish-taking-over-the-ocean)
The article is based on the following paper (for which the pdf is available - please send me a pm if interested and I will e-mail it):
Sanz-Martin, M. et al. (2016). Flawed citation practices facilitate the unsubstantiated perception of a global trend toward increased jellyfish blooms. Global Ecolology and Biogeography, 25: 1039-1049.
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Is there also an increase in jellyfish? I've seen quite a bit of reference to it in the last few years.
Not really...
http://www.bbc.com/earth/story/20160905-are-swarms-of-jellyfish-taking-over-the-ocean (http://www.bbc.com/earth/story/20160905-are-swarms-of-jellyfish-taking-over-the-ocean)
The article is based on the following paper (for which the pdf is available - please send me a pm if interested and I will e-mail it):
Sanz-Martin, M. et al. (2016). Flawed citation practices facilitate the unsubstantiated perception of a global trend toward increased jellyfish blooms. Global Ecolology and Biogeography, 25: 1039-1049.
Thanks bud... So that would explain lots of the "noise" that we're hearing, though it's still not definitive... It only discusses the dodgy citations and assumptions by some scientists. Obviously someone has sampled the oceans and has empirical data. I'd like to know what the situation really is.
Any idea what general influence the increase in cephalopods will have, other that reducing the price of calamari.
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Thanks bud... So that would explain lots of the "noise" that we're hearing, though it's still not definitive... It only discusses the dodgy citations and assumptions by some scientists. Obviously someone has sampled the oceans and has empirical data. I'd like to know what the situation really is.
Any idea what general influence the increase in cephalopods will have, other that reducing the price of calamari.
Fishing down the food-web.... Pretty much anything that swims the oceans eats squid. It is known that the biomass of ocean predators has been plundered (reduction of 66% to 80% - Myers & Worm, 2003; Christensen et al., 2014) in the last 100 years. This obviously results in the increase of prey species, not only squid... this has been fairly well documented.
I would guess, the same applies to jellyfish. Marine turtles are one of the most important predators of jellyfish (all turtles eat jellyfish in their juvenile phase which lasts up to 15-20 years!). Leatherbacks eat jellyfish all their life. Kill turtles -> more jellyfish! However it seems like the evidence has not amounted sufficiently to clearly establish what's going on. What has been reported is that the populations of jellyfish fluctuate a lot, but no steady trend has been detected...
As to your last question: don't know.... total collapse of the ecosystem!? Cephalopods are predators too... they eat fish, crustaceans, other cephalopods... etc... In practical terms, I guess a lot more people will be eating bait in the near future :hehe:
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:tkx:
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Changes in recreational shore anglers’ attitudes towards, and awareness of, linefish management along the KwaZulu-Natal coast, South Africa
* Management of recreational fisheries cannot be based on biological and stock assessment data alone but needs to include appropriate social aspects (including knowledge, attitudes and behaviour) of anglers within the fishery;
* The primary purpose of this study was to evaluate and complement existing recreational fisheries research, through the analysis of demographic and psychographic angler attributes collected from two independent, shore-based snapshot monitoring surveys conducted on the KwaZulu-Natal (KZN) coastline of South Africa, in 1994–1996 and 2009–2010;
* Results show significant changes between the two survey events in the demographics of anglers (including ethnic composition, age distribution, years of fishing experience and employment status) participating in the KZN shore-based linefishery;
* Traditional management regulations (minimum size limits, daily bag limits and closed seasons), though appearing to have support, have had limited effectiveness, based on the increased levels of admitted non-compliance and poor knowledge of regulations for target species;
* Anglers in both surveys believed that catches had declined over the years, with overfishing being the most common reason given;
* The results are discussed in the context of changing management practices in the KZN recreational shore-based linefishery. The implications of changes in fisheries management policies and responsibilities along the KZN coast are highlighted.
pdf available.
Reference:
Kramer, R. W., B. Q. Mann, S. W. Dunlop, J. B. Mann-Lang & D. Robertson-Andersson (2017). Changes in recreational shore anglers’ attitudes towards, and awareness of, linefish management along the KwaZulu-Natal coast, South Africa. African Journal of Marine Science, 39 (3): 327-337.
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Age and growth of narrow-barred Spanish mackerel Scomberomorus commerson in the coastal waters of southern Mozambique and KwaZulu-Natal, South Africa
* The narrow-barred Spanish mackerel Scomberomorus commerson is one of the most important linefish species caught in KwaZulu-Natal and southern Mozambique waters, forming the basis of important commercial, artisanal and recreational fisheries;
* A total of 439 S. commerson were sampled along the east coast of southern Africa (KwaZulu-Natal, South Africa, and southern Mozambique) between April 2011 and March 2012;
* Retrospective length-at-age data observed from whole otoliths were used to compare and describe sex-specific growth;
* Growth rates obtained from otolith-derived data were compared with those estimated from 29 tag-recaptured fish;
* Overall, ages ranged from 0.48 to 14.6 years for females and 0.4 to 13.57 years for males;
* Otolith readings yielded an average percent error of 11.21%, lower than recorded in a previous study from the region;
* Marginal zone analysis provided strong evidence that one translucent and one opaque growth zone were laid down annually;
* Schnute growth-function parameters indicated significant differences in growth between sexes;
* Females approached their mean asymptotic length at a faster rate, and grew to a greater mean length-at-age, relative to males;
* Growth in both sexes was rapid, achieving 67.46 cm FL (females) and 65.4 cm FL (males) in their first year of life;
* Growth rates obtained from tag-recaptured S. commerson indicated slower growth for smaller/younger fish up until 70 cm FL after which growth was very similar to that observed from otolith-derived data;
* The results of this study provide accurate, validated life-history parameters for king mackerel that are important for the assessment of
stock status in the region.
pdf available.
Reference:
Lee, B. & B.Q. Mann (2017). Age and growth of narrow-barred Spanish mackerel Scomberomorus commerson in the coastal waters of southern Mozambique and KwaZulu-Natal, South Africa. African Journal of Marine Science, 39(4): 397–407.
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That's very rapid growth :Like:
Thanks for these snippets Marcos. I don't always understand everything they say but they are still informative.
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:tkx: Marcos :toppie:
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Global proliferation of cephalopods
* Human activities have substantially changed the world’s oceans in recent decades, altering marine food webs, habitats and biogeochemical processes;
* Cephalopods (squid, cuttlefish and octopuses) have a unique set of biological traits, including rapid growth, short lifespans and strong life-history plasticity, allowing them to adapt quickly to changing environmental conditions;
* There has been growing speculation that cephalopod populations are proliferating in response to a changing environment, a perception fuelled by increasing trends in cephalopod fisheries catch;
* To investigate long-term trends in cephalopod abundance, a global time-series of cephalopod catch rates (catch per unit of fishing or sampling effort) was assembled;
* It is shown that cephalopod populations have increased over the last six decades, a result that was remarkably consistent across a highly diverse set of cephalopod taxa;
* Positive trends were also evident for both fisheries-dependent and fisheries-independent time-series, suggesting that trends are not solely due to factors associated with developing fisheries;
* The results suggest that large-scale, directional processes, common to a range of coastal and oceanic environments, are responsible;
* This study presents the first evidence that cephalopod populations have increased globally, indicating that these ecologically and commercially important invertebrates may have benefited from a changing ocean environment.
pdf available.
Reference:
Doubleday, Z. A., et al. (2016). Global proliferation of cephalopods. Current Biology, 26: R406-R407.
I've seen the squid first hand explode, but can put it down as you said lower down, the predator numbers must be down. Most squid live very short lives and everything eats them so if there has been a slow and gradual increase, yeah it can only be the predators being less and less. I've seen their population locally and fairly recently being collapsed from overfishing, us being the predator there. With one change in the fishing pressure and an extra voluntary closed season for the industry at the second major spawn event of the year and I've seen the population explode in a very short space of time relatively. This last season was the best ever, in all the years apparently, just a few short years after being collapsed. That to me only shows that the population of predators are mostly gone with not much other pressure on the squid population as a whole aside form us. Which actually is good news for recovery of other fisheries as there is food, lots of it, we just need to give some fish a break and release breeding stock as a culture.
And no it won't affect the price at all..all our handline squid is blast frozen at sea, landed later and exported directly to spain so we must pay euro prices if we want to secure some to stay here for the bait or restuarant market. Simple as that. More so, the biggest cost is the diesel bill to run the freezers at sea..Which is set on the rand/dollar, so as the rand tanks it will only get more expensive..last three years with catches going up and up and UP, boat prices has been R50, R70 respectively and this season over R100..all set on euro exchange rate, the euro price has been constant. The euro price of that fat white (bleached and chemically tenderised) humbolt squid from argentina, that one eats in most restuarants and supermarkets is something like 1/5 to 1/10th of the prices of ours on international market.
Ja but there is/was lots of squid out there in the ocean off our coast these days.. a large whack of them got caught in the last month, but they were allowed to lay eggs prior and the beds had the biggest gathering ever seen on them of squid so it bodes well for predatory fish in the future. And it is now a very sustainable fishery with most of those squid going to die soon after laying and instead they were caught but were allowed to lay. I'm very impressed with our local industry that got together and got scientists to tell them what to do and did it, without waiting for government and are now reaping the rewards...if only recreationals would do the same..
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That's very rapid growth :Like:
Thanks for these snippets Marcos. I don't always understand everything they say but they are still informative.
Thanks, glad to know people actually read these!
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Movement patterns of an endangered fishery species, Lithognathus lithognathus (Sparidae), [White Steenbras] and the role of no-take marine protected areas as a management tool
* Understanding movement behaviour is essential for effective management of fishery species;
* Dart tags were used to study coastal movement patterns of white steenbras Lithognathus lithognathus, an overexploited seabream
(Sparidae) in South Africa;
* In total, 6 962 fish (190–1 080 mm fork length) were tagged throughout the species’ distributional range, in four long-term fish-tagging programmes;
* The predominant behaviour recorded was residency, with relatively short-ranging movements;
* More than 60% of the 351 recaptured fish were recaptured within 1 km of their tagging site, some of which were at liberty in excess of three years;
* Most of the juveniles (93.9%), subadults (71.7%) and adults (64.0%) were recaptured within 10 km;
* Occasional long-distance movements of up to 800 km were recorded;
* Recapture distances were positively, but weakly, correlated with fish fork length (n = 257 fish measured at recapture; r2 = 0.166, p < 0.001);
* Low levels of connectivity among coastal areas suggest that large-scale annual spawning migrations, as previously hypothesised for this species, are unlikely, which raises the possibility of multiple spawning sites;
* Seventy-seven percent of L. lithognathus tagged within three marine protected areas (MPAs) were recaptured within the same MPA, suggesting that area closures provide protection for L. lithognathus through the post-estuarine juvenile, subadult and adult life stages;
* It is confirmed that the country’s current network of coastal MPAs plays a vital role in sustaining this species, and it is suggest that additional closures,
or otherwise substantial reductions in catch rates, are necessary for the species’ recovery.
pdf available.
Reference:
Bennett, R. H., P. D. Cowley, A.-R. Childs, C. G. Attwood, L. Swart & T. F. Næsje (2017). Movement patterns of an endangered fishery species, Lithognathus lithognathus (Sparidae), and the role of no-take marine protected areas as a management tool. African Journal of Marine Science, 39: 475-489.
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"1 080 mm fork length" :shk :Like: :Like: :Like:
Good for the MPAs... Now we just need to enforce them better... For EVERYONE.
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http://roaring.earth/publish-this-shark-ate-a-foreign-object-and-it-came-out-of-its-skin/ (http://roaring.earth/publish-this-shark-ate-a-foreign-object-and-it-came-out-of-its-skin/)
Full paper:
* A wild lemon shark (Negaprion brevirostris) was observed to expel an ingested foreign object through its body wall, over a minimum period of 435 days.
* The lemon shark was observed at a recreational diving feeding site off the coast of Juno Beach (FL, USA) on 12 occasions between 6 December 2014 and 14 December 2016.
* At the final observation, following expulsion, the lemon shark was observed with scar tissue and in apparent healthy condition.
* At minimum, this lemon shark was able to survive for over 1 year under perforation of its stomach lining, coelom and body wall.
* This account provides further evidence for the resilience and recovery capabilities of elasmobranch fish.
pdf available.
Reference:
Kessel, S. T. & J. Fraser, W. G. van Bonn, J. L. Brooks, T. L. Guttridge, N. E. Hussey & S. H. Gruber (2017). Transcoelomic expulsion of an ingested foreign object by a carcharhinid shark. Marine and Freshwater Research, 68 (11): 2173-2177.
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Thats incredible! Expelled a steel spike from it's stomach, out through it's skin!! :shk
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Hi John F - I enjoy and am enlightened by this periodic information but might I ask that you include the common name in the title or opening paragraph at least. Something like:
"endangered fishery species, Lithognathus lithognathus (Sparidae), " - commonly known as White Steenbras.
It's not always apparent in the subtext what is being referred to. And thank you for sharing!
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Hi John F - I enjoy and am enlightened by this periodic information but might I ask that you include the common name in the title or opening paragraph at least. Something like:
"endangered fishery species, Lithognathus lithognathus (Sparidae), " - commonly known as White Steenbras.
It's not always apparent in the subtext what is being referred to. And thank you for sharing!
Noted. Will try my best.
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Fascinating that it could actually find it's way through the stomach lining.
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Population connectivity of an overexploited coastal fish, Argyrosomus coronus (Sciaenidae), in an ocean-warming hotspot
* The West Coast dusky kob Argyrosomus coronus is a commercially exploited fish with a distribution confined to the Angola - Benguela Frontal Zone (ABFZ) of the southeastern Atlantic Ocean;
* A previous study revealedthat during a recent period of local warming the species extended its distribution into Namibian waters, where
it hybridised with the resident and congeneric Argyrosomus inodorus;
* Environmental changes are a majorthreat to marine biodiversity and when combined with overfishing have the potential to accelerate the decline
of species.
* However, little is known regarding the evolutionary history and population structure of A. coronus across the AB FZ.
* The genetic diversity, population structure and historical demographic changes were investigated using mtDNA control region sequences and genotypes at six nuclear microsatellite loci, from 180 individuals;
* A single, genetically homogeneous population was indicated across the distributional range of A. coronus;
* These findings imply that the oceanographic features within the ABFZ do not appearto significantly influence population connectivity in A. coronus, which simplifies management of the species;
* However, reconstruction of the demographic history points to a close link between the evolutionary history of A.c oronus and the environmental characteristics of the ABFZ;
* This outcome suggests the species' vulnerability to the rapid environmental changes being observed across this region, and highlights a pressing need for transboundary management to mitigate the impacts of climate change in this global hotspot of seawater temperature changes.
pdf available.
Reference:
Henriques, R., W. M. Potts, C. V. Santos, W. H. H. Sauer & P. W. Shaw (2018). Population connectivity of an overexploited coastal fish, Argyrosomus coronus (Sciaenidae), in an ocean-warming hotspot. African Journal of Marine Science 40: 13-24.
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http://science.sciencemag.org/content/360/6389/642 (http://science.sciencemag.org/content/360/6389/642)
"Big mamas matter for fish
The theoretical relationship between reproduction and body size has assumed that total mass relates directly to fecundity, regardless of the number of individuals involved. This assumption leads to fisheries management practices that suggest that one large female fish can be replaced by several smaller females. However, this assumption is incorrect. Barneche et al. show that larger females are far more productive than the same weight's worth of smaller females. Management practices that ignore the value of large females could contribute to unexplained declines seen in some fish stocks.
Science, this issue p. 642 (http://science.sciencemag.org/lookup/doi/10.1126/science.aao6868)
Abstract: Body size determines total reproductive-energy output. Most theories assume reproductive output is a fixed proportion of size, with respect to mass, but formal macroecological tests are lacking. Management based on that assumption risks underestimating the contribution of larger mothers to replenishment, hindering sustainable harvesting. We test this assumption in marine fishes with a phylogenetically controlled meta-analysis of the intraspecific mass scaling of reproductive-energy output. We show that larger mothers reproduce disproportionately more than smaller mothers in not only fecundity but also total reproductive energy. Our results reset much of the theory on how reproduction scales with size and suggest that larger mothers contribute disproportionately to population replenishment. Global change and overharvesting cause fish sizes to decline; our results provide quantitative estimates of how these declines affect fisheries and ecosystem-level productivity."
https://www.eurekalert.org/multimedia/pub/169835.php (https://www.eurekalert.org/multimedia/pub/169835.php)
https://www.eurekalert.org/pub_releases/2018-05/aaft-bmf050718.php (https://www.eurekalert.org/pub_releases/2018-05/aaft-bmf050718.php)
"Even accounting for their proportionate size, bigger female fish produce many more offspring than smaller fish, a new study reveals. The results hold implications for fisheries managers, since climate change is expected to reduce the size of fish (and thus the number of their offspring) in many regions around the globe. The question of whether reproduction scales with size has been hotly debated. Theories and fisheries models assume that the reproductive output of one 2-kilogram (kg) fish is equal to that of two 1-kg fish; yet field biologists have repeatedly suggested that fecundity of fish may increase disproportionately with body mass. To better understand this likelihood, Diego R. Barneche et al. analyzed the total reproductive-energy output of 342 species of marine fish. Indeed, in the majority of species, they found a scaling pattern where bigger mothers produce exponentially more offspring. For example, a single 30-kg female produces more eggs than about 28 2-kg females (that collectively weigh 56 kg); as well, a batch of eggs from a 30-kg female harbors 37 times the total energy content of a batch from her 2-kg counterpart. These results emphasize the importance of larger fish for replenishing marine fish populations, the authors say. Estimates of size reductions for the Atlantic mackerel (Scomber scombrus) predicted to occur in the face of climate change, would result in a 50% per capita reduction in fecundity for the species, say the authors. In good news, marine protected areas have been found to increase fish size, pointing to at least one solution for more sustainable fisheries in the future."
https://www.monash.edu/science/news/current/wrong-assumptions-about-how-organisms-reproduce-threatens-world-fisheries,-study-warns (https://www.monash.edu/science/news/current/wrong-assumptions-about-how-organisms-reproduce-threatens-world-fisheries,-study-warns)
Here in sa..daff is fast asleep, scientists been calling for slot limits and limit changes for more than a decade..No policing these days anyway so would it matter? Gillnets are choking the estauries and impoundments while the government sees fit to start and industry inland in pristine waters where endangered species swim. Daff, msc and sassi still think the shallow water hake trawl is a "green choice", meanwhile the fishery catches (and sells) more bycatch than hake (and for more value than hake). Sassi is not even aware it seems of the squid that gets targeted and others by the trawl. It has now listed geelbek as red even though it is actively targetted by the trawl along with shark, reef fish, skates, cob etc..we in the dark ages of marine management in SA. There is no concept of education in SA from the government to the fishing masses as to sustainable fishing practices, by their actions it seems those in charge do not even have any idea themselves. In fact they seem to be helping themselves to the bounty of the ocean at everyone elses expense, daff and Zboy recently being implicated in perlie syndicates dealing and what with the state/PIC being decent shareholders in the shallow water hake and squid industries though their less than independant sekunjalo investment so don't except changes in the "green" there status anytime soon.
But anyway its now official, again..BigFatFecundFemales support the stocks.. Release the big breeding fish if you want your kids to still catch them. Gov's not going to do anything to save the stocks, we may as well do our bit. What was the result of research in SA, around 90% of baby cob sampled around the coast came from less than 1000 females, and they are interbreeding with silver cob as there are not enough breeders of dusky left, there are probably less than 1000 BFFF dusky cobs are left in total (on our whole coast line) to support that stock, they are actually rarer than the rhino. What has been done as a result? Nudda. Zilch. No slot limits, no urgent intervention from Daff, no alerting off the masses or education campaigns, commercial harvesters can and do still target them with no limit on size or amount and the inshore hake trawl can target and net them and do, and sell them as they wish and their fishery is "green" and it's all cool..Business as usual..Most of the commercials I have met in my life are not even aware of the fecundity of fish relative to size, even though it has been common knowledge in fisherfolk in some parts of the world for nearly 20 years?
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(https://media.eurekalert.org/multimedia_prod/pub/web/169835_web.jpg)
https://media.eurekalert.org/multimedia_prod/pub/web/169835_web.jpg (https://media.eurekalert.org/multimedia_prod/pub/web/169835_web.jpg)
That last graph looks like what happened to the SBFT (which is now slowly recovering) and that graph looks like what happened to our dusky cob, leervis, red steenbras, poenskop, red stumps and a whole host of other reef fish. If you handle the large fish with care and put them back the graph goes up! If there are enough large fish left it is that easy and that simple..if there are not, the species never recovers back to unfished levels and reaches a new population equilibrium. That happened to one of the largest members of the cob family off mexico/california (that gets to well over 100kg but has all but dissapeared, it has never returned to most waters and the population is small but stable in a few places, that said the other members of the family there like the white seabass (sister species to our geelbek) has greatly benefitted from slot limits, education campaigns and hatchery programs and a change in commercial harvest methods and the stock mass and average size of fish are now better than before we fished them?! The average size of that fish now is bigger than the previous world record that stood for over 60 years. That fishery has shown scientists conclusively that we can improve a fishery to become even better than what it was during unfished levels if we fish selectively and restock fish from good genetics where we can. We can actually IMPROVE an unfished stock if we fish it right and the stock is of a relatively fast growing fish without any sex change ecology. Slow growing and slow to breeding fish that change sex must only be very carefully harvested in a careful slot of size, and cannot sustain commercially harvesting, without collapse, that includes most of our reef fish. These fish can sustain low pressure subsistence harvesting but only with very selective fishing and return of most fish and all breeding stock fish, any harvest of a more greedy nature and eventually the stock will collapse.
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Economic importance of recreational angling in SA
A multi-disciplinary study by researchers from Rhodes, Cape Town and North-West Universities, the South African Institute for Aquatic Biodiversity (SAIAB) and the Oceanographic Research Institute (ORI) on the economic impact of the recreational fishery in South Africa, which was recently commissioned by the South African Consolidated Recreational Angling Association (SACRAA) has revealed that in 2017 total spending by an estimated 1.3 million recreational anglers contributed R26.5 billion to the economy. The industry also supported 94 000 employment opportunities.
Report available here: http://www.sacraa.co.za/wp-content/uploads/2018/05/Recreational-fishing-report-2017-2.pdf (http://www.sacraa.co.za/wp-content/uploads/2018/05/Recreational-fishing-report-2017-2.pdf)
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R26 Billion! :shk
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I made a fair contribution but not quite R26bn.
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First known omnivorous shark species identified
https://www.theguardian.com/environment/2018/sep/05/bonnethead-omnivorous-shark-species-identified (https://www.theguardian.com/environment/2018/sep/05/bonnethead-omnivorous-shark-species-identified)
pdf of the paper is available. Those interested please let me know.
Reference:
Leigh SC, YP Papastamatiou & DP German (2018). Seagrass digestion by a notorious ‘carnivore’. Proceedings of the Royal Society B, 285: 20181583.
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Note to the Transkei anglers... try sliding some broccoli on your next outing :craz:
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Very interesting, wish some of our sharks will turn vegetarian.
Sharks are currently out of ontrol in the St Lucia area. Every decent fish is being taxed.
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Note to the Transkei anglers... try sliding some broccoli on your next outing :craz:
depends on how much transkei gold you found before you go fishing
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Note to the Transkei anglers... try sliding some broccoli on your next outing :craz:
depends on how much transkei gold you found before you go fishing
Hmmmm... Sliding an arm of TK gold... Could catch some wacky species. I wonder what else you could pick up on sea weed :creep:
... Apologies for going off topic Marcos :bow:
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The largest aggregation of giant trevally Caranx ignobilis (Carangidae) on record
:gt: :gt: :gt:
* The giant trevally Caranx ignobilis (Forsskål) is an important apex predatory fish typically associated with coral reef communities.
* It is prized in recreational and commercial fisheries, yet little is known about its aggregation dynamics and susceptibility to fishing pressure.
* This study reports on a previously undocumented aggregation of mature giant trevally observed over a period of eight years (2010–2017) at Ponta do Ouro Partial Marine Reserve in southern Mozambique.
* The aggregation is one of the few recorded for this carangid in the western Indian Ocean and represents the first subtropical aggregation of giant trevally.
* The aggregation is also the largest recorded for this species, with up to 2 413 individuals representing an estimated biomass of approximately 30 tonnes.
* The size and predictability of this annual aggregation make it vulnerable to overexploitation and point towards the need for an appropriate conservation management strategy.
PDf available.
Reference:
Daly R, CAK Daly, RH Bennett, PD Cowley, MAM Pereira & JD Filmalter (2018). Quantifying the largest aggregation of giant trevally Caranx ignobilis (Carangidae) on record: implications for management. African Journal of Marine Science, 40 (3): 315-321.
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30 tons of awesome fishing power... The stuff that dreams are made of. :tkx:
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:tkx: Also from me, thanks! Awesome..the spawn from the 30ton breeding machine is probably what makes it into the transkei rivers..You guys seen that video of the migration they do up the Mtentu river? (or used to do this year Sanral stuffed up the estuary in building the new N2 bridge and the GT's never came, if and when they try force the mining through of the coastal dunes then it will be a bugger for the nurseries for these fish)
https://www.youtube.com/watch?v=GKK93VAM-_w (https://www.youtube.com/watch?v=GKK93VAM-_w)
Big F'ing fish ;) I wonder if the aggregration studied in your post are one and the same that do the migration/pilgrimage to where they grew up as little marauders in the TK rivers?
http://aidc.org.za/famous-mtentu-river-damaged-by-up-stream-sand-from-sanrals-n2-mega-bridge-project/ (http://aidc.org.za/famous-mtentu-river-damaged-by-up-stream-sand-from-sanrals-n2-mega-bridge-project/)
Recent Mtentu news..
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Evaluating the effects of catch-and-release angling on Cape stumpnose Rhabdosargus holubi in a South African estuary
* Fisheries managers are increasingly promoting catch-and-release (C&R) to manage recreationally angled fishstocks;
* Despite this, there is a scarcity of information on the effects of C&R on estuarine-dependent species;
* Cape stumpnose Rhabdosargus holubi dominates the recreational fisheries catch and provides an important source of food for subsistence fishers in some temperate South African estuaries;
* The health and survival of R. holubi exposed to a C&R event was investigated by examining their physiological stress response (blood glucose and lactate), reflex impairment (reflex action mortality predictors [RAMP]) and short-term (12-hour) survival;
* Fish were captured and exposed to one of three air-exposure treatments: 0 s, 30 s or 90 s;
* Stress and health were measured either immediately (immediate) or one hour after (delayed) the C&R event;
* There was no significant difference in blood glucose between air-exposure treatments, but there was a significant difference between the mean immediate and delayed glucose levels within each treatment (F(2,143) = 81.8, p < 0.01);
* In contrast, blood lactate level was significantly higher in the 90-s treatment (p < 0.05);
* Immediate blood lactate levels were significantly lower than the delayed samples for each treatment (F = 4.29, p = 0.02; n = 169);
* Although all fish exhibited at least one reflex impairment, the RAMP score was significantly higher in the 90-s air-exposure treatment (H(2,86) = 9.73, p = 0.007);
* Also, RAMP scores were significantly lower in the delayed samples (p < 0.01);
* Although short-term mortality was relatively low (2.3%) for this species, it was highest in the 90-s treatment (7%);
* These results suggest that physiological stress is higher when R. holubi are exposed to longer periods of air exposure and that the
physiological stress of fish subject to a C&R event is best measured after a delay.
pdf available.
Reference:
Arkert NK, A-R Childs, MC Parkinson, AC Winkler, E Butler, S Mannheim & WM Potts (2018). Evaluating the effects of catch-and-release angling on Cape stumpnose Rhabdosargus holubi in a South African estuary. African Journal of Marine Science, 40(3): 235–244.
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Pretty much confirms the thinking of "get the fish back in the water asap". I get quite rattled when anglers spend too much time taking photos and faffing around. But at least this also debunks the myth that the bulk of fish caught die after release. Thanks bud.
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Fifty-five-year longevity for the largest member of the family Sparidae: the endemic red steenbras Petrus rupestris from South Africa
* A previous study that explored the age and growth of red steenbras Petrus rupestris (Valenciennes, 1830), a large sparid (family Sparidae, seabreams or porgies) endemic to South Africa and reported to approach 2 m in length, provided estimates as a moderately slow-growing species with a maximum age near 30 years;
* The stock is considered collapsed and a fishing moratorium was imposed in 2012, resulting in this species being assessed as Endangered by the IUCN;
* One consideration in addressing population status is validation of life-history traits;
* In this study, estimates of age for red steenbras from thin-sectioned otoliths were reassessed visually in terms of both the original ages and revised estimates using a different age-reading pattern;
* The revised ages exceeded the original ages by up to 30 years, with a maximum estimated age of 55 years from a well-defined otolith section that provided a basis for the revised age-reading procedure;
* Bomb radiocarbon (14C) dating revealed there was an offset in the timing of the 14C rise on the Agulhas Bank that, when coupled with considerations for regional oceanography, provided support for the revised age-reading pattern and an estimated longevity that exceeds 50 years;
* These findings were further supported by the fortuitous recapture of a tagged red steenbras that was at liberty for 22 years.
PDF available.
Refrence:
Andrews, A. H., M. J. Smale, P. D. Cowley & N. Chang (2018). Fifty-five-year longevity for the largest member of the family Sparidae: the endemic red steenbras Petrus rupestris from South Africa. African Journal of Marine Science, 40 (4): 343-353.
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Thanks for sharing!Wow,imagine catching a fish that's been living in the ocean for longer than I've been alive!That's amazing...should call these older fish OOM before releasing..lol
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That's bloody old... Show these fish some :resp:
Thanks Marcos :uarocks
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Marcos :resp: :bow: always enjoy your posts . :tkx: :toppie:
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Interesting!! :sshine:
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Movement patterns of an endemic South African sparid, the black musselcracker Cymatoceps nasutus, determined using mark-recapture methods
* This study made use of data from three long-term fish tagging projects along the South African coastline to investigate the movement behaviour of the endemic black musselcracker Cymatoceps nasutus (Sparidae).
* From 1984 to 2016, a total of 3 430 C. nasutus (178–980 mm fork length) were tagged (with small plastic dart tags) throughout the species’ distributional range, with an overall reported recapture rate of 7.2%.
* Recaptured individuals displayed high levels of residency, moving an average of 14.8 km, with time-at-liberty ranging from 0 to 6 809 days.
* The majority of recaptures (84.6%) were made within 1 km of the tagging sites; however, some large-scale movements, of up to 528 km, were recorded.
* Although C. nasutus individuals moving greater distances were characterised by greater mean sizes (mm fork length) at time of recapture, the distances moved by juveniles were not significantly different from those of adults (p > 0.05).
* Low levels of connectivity among coastal regions were therefore expected due to the high degree of residency displayed by this species.
* Combining traditional management approaches together with a well-designed network of no-take marine protected areas is likely to be the most effective way to protect this vulnerable species.
* A lack of data on the movements of adults remains a challenge, but this could be overcome by tracking large individuals tagged with long-life acoustic transmitters.
PDF available.
Reference:Murray, T. S., P. D. Cowley, B. Q. Mann, J. Q. Maggs & G. Gouws (2019). Movement patterns of an endemic South African sparid, the black musselcracker Cymatoceps nasutus, determined using mark-recapture methods. African Journal of Marine Science, 41: 71-81.
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don't know if this the correct place to post this - Hi all, just wanted to know if any of you noticed the abundance of the lantern bream fish mostly on the north coast including Umhlanga Rocks as well.
I have seen fishermen catching more than their quota and this fish is coming out thick all over - some of them were in the 2 till two and a half kg weight category however its very sad to see that they are taking so many of these fish out . I saw a guy catch 16 of this and he bagged all 16 I saw another couple of guys catching around the same number as well. are these fish facing any challenges ? its my first time in my fishing career seeing this.
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First marlin archival tagging study suggests new direction for research
* Decades of billfish tagging studies have been hindered by below-par conventional tag recovery rates and high rates of premature satellite pop-up tag shedding.
* With hopes of obtaining long-term tracking data, the world’s first archival tagging study on an istiophorid was performed, by surgically implanting 99 archival tags into the peritoneal cavity of
striped marlin (Kajikia audax) off the coast of Baja California, Mexico.
* Marlin were also tagged externally with a conventional tag before release.
* Ten archival tags (10.1%) were recovered with days at liberty (DAL) ranging from 400 to 2795.
* Nine recoveries were from Mexican waters, whereas one marlin was recaptured off Ecuador.
* In total, 100% of the light stalks on the archival tags failed, with nine failing within the first 3 months of deployment; because the light data are used to estimate the geographic position of the tagged fish, tracking data were compromised.
* The absence of conventional tags on all recaptured marlin indicates that studies of marlin using conventional tags have been hindered by tag shedding
rather than tagging-associated mortality or underreporting.
* The high recapture rate and long DAL suggest istiophorid science could be greatly advanced by archival tagging if new tag designs or methods can eliminate tag failure.
PDF available.
Reference:
Domeier, M. L., S. Ortega-Garcia, N. Nasby-Lucas & P. Offield (2019). First marlin archival tagging study suggests new direction for research. Marine & Freshwater Research, 70: 603-608.
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Basically, all tagging done by recreational anglers is pretty much useless!!!!!
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Basically, all tagging done by recreational anglers is pretty much useless!!!!!
I take it you are referring only to Marlin?
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Basically, all tagging done by recreational anglers is pretty much useless!!!!!
I take it you are referring only to Marlin?
Yes.
Results on other species are overwhelmingly clear and unequivocal.
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Acoustic telemetry reveals multi-seasonal spatiotemporal dynamics of a giant trevally Caranx ignobilis aggregation
* Predictable fish aggregations of commercially valuable species are particularly susceptible to overexploitation.
* Giant trevally Caranx ignobilis are ecologically important top predatory fish targeted in both recreational and commercial fisheries; however, little is known about their aggregation dynamics or susceptibility to overexploitation.
* This study employed acoustic telemetry to investigate the temporal and spatial characteristics of one of the largest known aggregations of this species over a 3 yr period in a marine protected area in Mozambique, West Indian Ocean.
* Tagged fish were monitored for between 386 and 1176 d, during which they exhibited distinct aggregative periods in austral spring and summer.
* The detection frequency of fish at the aggregation site was significantly associated with rising mean sea temperatures and the full moon period.
* Whilst at the aggregation site, fish exhibited clear patterns of diel periodicity, with maximum hourly detections recorded during midday.
* All fish exhibited periods of absence from the aggregation site between summer seasons, in which time many of them ranged across an international border for distances of between 11 and 633 km before returning to aggregate at the same site in the following season.
* These results confirm that the studied giant trevally aggregation is temporally and spatially predictable, and consistent with a transient site-specific fish spawning aggregation.
* The spatiotemporal predictability of the aggregation highlights the need for the effective management of this transboundary population of giant trevally, for which this study has provided conservation management recommendations.
PDF available.
Reference:
Daly, R., J.D. Filmalter, C.A.K. Daly, R.H. Bennett, M.A.M. Pereira, B.Q. Mann, S.W. Dunlop & P.D. Cowley (2019). Acoustic telemetry reveals multi-seasonal spatiotemporal dynamics of a giant trevally Caranx ignobilis aggregation. Marine Ecology Progress Series, 621: 185-197.
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This has puzzled me for years... Do they have any clues as to why they do it?
For those who don't know (I didn't)... Definition of diel. : involving a 24-hour period that usually includes a day and the adjoining night diel fluctuations in temperature.
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Great info! :+ cred:
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:tkx: :toppie:
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Can long-term content analysis of print media be used to examine species composition, population demography and changes in distributional range of recreational fishery species?
* Although marine recreational fisheries are socially and economically important, there is often limited funding for their monitoring and assessment.
* With South African anglers reporting catch declines for almost all targeted species and little long-term monitoring data available, novel methods need to be explored to provide managers with additional information.
* This study aimed to evaluate the efficacy of content analysis of print-media records for detecting long-term trends in species composition, size composition and distribution of selected recreational fishery species.
* Information for eight fishes captured in the marine shore-based fishery was collected from South Africa’s most popular recreational fishery magazine, between 1960 and 2009.
* During the five decades, there were shifts in the catch composition, from being dominated by slow-growing, large predators to faster-growing, large predators and lower-trophic-level species.
* There were no significant trends in the mean and maximum sizes of the dominant species, except for dusky kob Argyrosomus japonicus, which increased significantly in the maximum
size reported during the study period.
* The distributional range of A. japonicus and leervis Lichia amia significantly increased, and that of galjoen Dichistius capensis significantly decreased.
* However, it was uncertain whether these trends could be attributed to population changes, changes in angler technology and/or behaviour, or climate signals.
* Overall, this type of content analysis may provide a cost-effective method to examine changes in species composition and fish distributions over time, but, without detailed knowledge of shifts in angler behavioural patterns, it may not be as useful for understanding changes in the population dynamics of recreational fishery species.
* It is suggested that fishery-independent monitoring programmes are most suited for this type of complex fishery.
pdf available.
Reference:
Potts, W. M., T. Jordan & A.-R. Childs (2019). Can long-term content analysis of print media be used to examine species composition, population demography and changes in distributional range of recreational fishery species? African Journal of Marine Science 2019, 41(3): 231–245.
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Very interesting reading! So we got good at catching the big cob, and perhaps also better at catching the leeries (Anecdotally from the old timers the leeries were in all the haunts they are now, in the old days, but in much much larger numbers of far larger fish in the old days. The galjoen has been hammered and we have fished out the red and black steenbras.
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All the more reason to keep catch reports flowing on responsible social media like UA. :Like:
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Growth Limitation of Marine Fish by Low Iron Availability in the Open Ocean
* It is well-established that phytoplankton growth can be limited by the vanishingly low concentrations of dissolved iron found in large areas of the open ocean;
* However, the availability of iron is not typically considered an important factor in the ecology of marine animals, including fish;
* Observations that show that the iron contents of lower trophic level organisms in iron-limited regions can be an order of magnitude less than the iron contents of most fish were compiled;
* Although this shortfall could theoretically be overcome if iron assimilation rates were very high in fish, observations suggest this is not the case, consistent with the high recommended iron contents for mariculture feed;
* In addition, two occurrences among fish living in iron-poor regions that would conceivably be beneficial given iron scarcity are highlighted: the absence of hemoglobin in Antarctic icefish, and the anadromous life history of salmon;
* Based on these multiple lines of evidence, it is suggested that the iron content of lower trophic level organisms can be insufficient to support many fish species throughout their life cycles in iron-poor
oceanic regions;
* A global satellite-based estimate of fishing effort was used to show that relatively little fishing activity occurs in high nitrate low chlorophyll (HNLC) regions, the most readily identified iron-poor domains of the ocean, particularly when compared to satellite-based estimates of primary production and the observed mesozooplankton biomass in those waters;
* The low fishing effort is consistent with a low abundance of epipelagic fish in iron-limited regions, though other factors are likely to contribute as well;
* The results imply that the importance of iron nutrition extends well beyond plankton and plays a role in the ecology of large marine animals.
pdf available.
Reference:
Galbraith, E. D., P. Le Mézo, G. S. Hernandez, D. Bianchi & D. Kroodsma (2019). Growth limitation of marine fish by low iron availability in the open ocean. Frontiers in Marine Science, 6: 509. doi: 10.3389/fmars.2019.00509
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Life history, distribution and seasonal movements of a threatened South African endemic seabream, Chrysoblephus gibbiceps
* The red stumpnose Chrysoblephus gibbiceps (Sparidae) is a South African endemic seabream that has been severely depleted by fishing.
* A total of 678 C. gibbiceps were sampled by line and trawl fishing for a study of their morphology, age, growth, reproduction and diet. In addition, catch records from three time-periods since 1897 were interrogated for distribution patterns and movement behaviour.
* The sex ratio was 1.5:1 in favour of males. The length–weight relationship, W = 9.32 × 10−5 LF 2.811, indicates hypoallometric growth.
* The bulbous head of large males is a secondary sexual characteristic.
* A von Bertalanffy growth model was fitted to age data obtained using otolith analyses: LF = 429.9 × (1 – e−0.113(t – (−3.799)).
* The maximum recorded age was 48 years, which is among the highest in seabreams, though the species matures after only 3 years.
* The gonadosomatic index (GSI) of ripe females (4.5%) was comparatively low, and the two-month-long early-summer spawning season was short compared with that of other sympatric seabreams.
* The very low GSI of ripe males (1.6%) suggests courtship battles and polygamy.
* The species feeds over low-profile reefs and consolidated sediments.
* The principal prey are ophiuroids.
* Although its trophic level is 3.7, C. gibbiceps has a low-nutrition diet.
* Historical and current catch data confirm a distribution from Cape Point (southeastern Atlantic) to southern KwaZulu-Natal Province (western Indian Ocean).
* There is evidence for localised migratory patterns, now partly lost due to severe population depletion.
* Whereas protogyny and resident behaviour have been suggested as traits that render seabreams vulnerable to fishing pressure, C. gibbiceps is a shoaling gonochorist that has collapsed due to fishing.
pdf available.
Reference:Attwood, C. G., M. E. Dawson, S. E. Kerwath & C. Wilke (2019). Life history, distribution and seasonal movements of a threatened South African endemic seabream, Chrysoblephus gibbiceps. African Journal of Marine Science, 41 (4): 395-411.
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Thanks Marcos... And thank you for keeping this thread going.
The sex ratio... I wonder if that's actual or of those caught... Any idea?
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The sex ratio is of those 678 fish sampled. It is usually assumed that the sample is random (unless there's evidence that points otherwise), and thus indicative of the actual situation.
That's why sample size is crucial... and you will always hear biologists (or any scientist for that matter!), cry over sample size and claiming more studies are needed (well, also need to pay the bills heheheheh)
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I was wondering if males are just more stupid (and prone to getting conned by anglers) than females... w;k
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Well, usually males of any species are more stupid :hyst: ... but don't really think it matter in this case...
However, in some species (the hammerhead shark for example), are notorious for large aggregation of females .... and these could potentially be risky in terms of wiping out females or males...
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Spatial trophic variability of a coastal apex predator, the giant trevally Caranx ignobilis, in the western Indian Ocean
* Top predators have substantial downstream effects on the structure, function, and resilience of ecosystems.
* The influence of top predators on an ecosystem can vary if they occur within multiple habitat types and have a wide niche breadth due to spatiotemporal changes in diet.
* The spatial patterns in trophic position and niche width for an economically important reef-associated fishery species, the giant trevally Caranx ignobilis were examined.
* Four localities in the western Indian Ocean representing different habitats: coral atolls, coastal reefs, and granitic islands were sampled.
* Isotopic ratios of carbon (13C/12C) and nitrogen (15N/14N) were analyzed, compound-specific amino acid stable isotope analysis (AA-CSIA) performed to control for baseline nitrogen variation.
* The analysis of 12 juveniles and 43 adults revealed wide variation in trophic niche breadth between sampling sites and an offshore to coastal gradient in carbon that drove niche distinctiveness between localities.
* Niche width patterns suggestive of ontogenetic changes in diet and habitat utilization and larger niche sizes at the oceanic island sites than the coastal site were observed.
* Trophic position estimates ranged from 3.5−5, expanding the trophic range of C. ignobilis relative to previous studies using AA-CSIA and placing it at the equivalent trophic level as many predatory sharks.
* The study corroborates prior evidence that C. ignobilis is an important apex predator in reef and island ecosystems.
* It is shown how evaluating spatiotemporal components of trophic ecology of marine predators is critical for characterizing their functional
role and ecosystem influence, allowing for targeted conservation efforts.
pdf available.
Reference:Glass, J. R., R. Daly, P. D. Cowley & D. M. Post (2020). Spatial trophic variability of a coastal apex predator, the giant trevally Caranx ignobilis, in the western Indian Ocean. Marine Ecology Progress Series, 641: 195-208.
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And now in English? duh
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hahahah here it goes:
* GTs are important predators (same trophic level as many sharks) that take on a large variety of prey items;
* Juvenile GTs prey on different items comparing with adults (the diet changes with age)
* GTs from oceanic islands have a slightly different diet comparing to those in coastal (=continental) areas!
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Interesting info , thx Marcos ... will have to change my tactics when at the sea again ... :hnthnt:
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will have to change my tactics when at the sea again ... :hnthnt:
Are we ever going to be allowed back to the ocean :blush:
Thanks Marcos... The translation was useful w;k ... They really are apex predators... Fight clubbers of the reef, as opposed to Sharks, which IMHO are opportunists of the reef. That's what makes geets such an awesome target.
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Ecosystem service values of sediment generation and entrapment by marginal coral reefs at Sodwana Bay, South Africa
* Coral reefs provide a multitude of goods and services, some of which are difficult to value due to their intangible nature and the absence of markets to ascribe their relative worth;
* The coral reefs of Sodwana Bay on the northeast coast of South Africa provide several ecological goods and services, of which only two are considered here: namely, sediment generation and sediment entrapment;
* Both are deemed essential to the functioning of the Sodwana Bay economy;
* The replacement-cost method was used to estimate the annual financial cost of sediment provided to the study area if it were replaced by dredging;
* Sediment generation by the coral reefs was valued at R2.6–R4.8 million, and sediment entrapment valued at R71.8–R84.6 million, totalling between R74.4 million and
R89.4 million (≈$5.6–$6.7 million, at R13.38/US$1) per year;
PDF available.
Reference:
Laing, S. C. S, M. H Schleyer & J. K. Turpie (2020). Ecosystem service values of sediment generation and entrapment by marginal coral reefs at Sodwana Bay, South Africa. African Journal of Marine Science, 42 (2): 199-207.
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Giant trevally (Caranx ignobilis) of Hawaiian Islands can live 25 years
* Giant trevally (Caranx ignobilis) are an iconic reef fish of the Indo-Pacific, and yet knowledge of their life history is incomplete.
* The species is common in tropical and subtropical waters ranging from the far western Indian Ocean off South Africa to the central Pacific Ocean,
where the species attains its greatest recorded size in Hawaii.
* Despite their broad range, importance as a top predator and attraction among anglers, the age and longevity of giant trevally remain largely undescribed and there are concerns that giant trevally are being fished down in the Hawaiian Islands.
* The most comprehensive age and growth study was performed in the Hawaiian Islands, but the work was limited to early growth observations.
* Although a study of daily increments was limited to fish less than maximum size, a model used to describe the growth characteristics was extrapolated to estimate that maximum age may exceed 20 years.
* In this study, otoliths of giant trevally from the Hawaiian Islands were investigated for annual growth zones, and the validity of the age estimates was tested and validated with bomb 14C dating.
* Revised growth parameters indicate giant trevally grow rapidly in the Hawaiian Islands and can attain an age of 25 years.
pdf available.
Reference:
Andrews, A. H. (2020). Giant trevally (Caranx ignobilis) of Hawaiian Islands can live 25 years. Marine & Freshwater Research, 71(10) 1367-1372.
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Giant trevally (Caranx ignobilis) of Hawaiian Islands can live 25 years
* Giant trevally (Caranx ignobilis) are an iconic reef fish of the Indo-Pacific, and yet knowledge of their life history is incomplete.
* The species is common in tropical and subtropical waters ranging from the far western Indian Ocean off South Africa to the central Pacific Ocean,
where the species attains its greatest recorded size in Hawaii.
* Despite their broad range, importance as a top predator and attraction among anglers, the age and longevity of giant trevally remain largely undescribed and there are concerns that giant trevally are being fished down in the Hawaiian Islands.
* The most comprehensive age and growth study was performed in the Hawaiian Islands, but the work was limited to early growth observations.
* Although a study of daily increments was limited to fish less than maximum size, a model used to describe the growth characteristics was extrapolated to estimate that maximum age may exceed 20 years.
* In this study, otoliths of giant trevally from the Hawaiian Islands were investigated for annual growth zones, and the validity of the age estimates was tested and validated with bomb 14C dating.
* Revised growth parameters indicate giant trevally grow rapidly in the Hawaiian Islands and can attain an age of 25 years.
* They are the most awesome fish in the ocean.
Reference:
Andrews, A. H. (2020). Giant trevally (Caranx ignobilis) of Hawaiian Islands can live 25 years. Marine & Freshwater Research, 71(10) 1367-1372.
There... Fixed it w;k
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Agree with Fishstyx! :gt:
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"I would die to see one": A study to evaluate safety knowledge, attitude, and behavior among shark SCUBA divers
* Shark diving tourism is an activity that can contribute significantly to coastal economies, while also offering tremendous help to shark conservation efforts.
* Nevertheless, like any form of wildlife-based tourism, shark diving poses management challenges revolving around ethical and safety considerations.
* Safety in shark diving normally focuses on operational self-efficacy and adherence to shark diving codes of conduct to prevent incidents such as shark bites and to minimize ecological harm.
* However, safety issues in shark diving can arise from personal choices to exceed standard certification limits.
* Any detrimental results are capable of casting doubts on the sustainability of shark diving, thus jeopardizing its future as well as shark conservation.
* This study addressed compliance with shark diving codes of conduct and standard diving safety by examining the knowledge, attitude, and behavior of people who engage in free scuba diving with predatory sharks.
* The research made use of mixed methods of data collection, including interviews with shark divers at two popular shark diving destinations in Southeast Africa (n = 86) and an online questionnaire survey among shark divers (n = 89).
* The results showed that divers had positive attitudes towards sharks and shark diving.
* However, a notable proportion declared that they had exceeded certification limits and broken codes of conduct during shark diving.
* In particular, diving experience and being a professional diver were correlated significantly with poor safety attitudes and behavior.
* The results highlight the need to create an understanding among scuba divers of the connection between shark diving safety and conservation, including the negative implications of safety breaches, whether big or small, for the future of shark diving tourism and of sharks.
PDF available.
Reference:
Lucrezi, S., F. Bargnesi & F. Burman (2020). "I would die to see one": A study to evaluate safety knowledge, attitude, and behavior among shark SCUBA divers. Tourism in Marine Environments, 15 (3-4): 127-158.
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Maximum swimming speeds of sailfish and three other large marine predatory fish species based on muscle contraction time and stride length: a myth revisited
* Billfishes are considered to be among the fastest swimmers in the oceans.
* Previous studies have estimated maximum speed of sailfish and black marlin at around 35 m s−1 but theoretical work on cavitation predicts that such extreme speed is unlikely.
* This study we investigated maximum speed of sailfish, and three other large marine pelagic predatory fish species, by measuring the twitch contraction time of anaerobic swimming muscle.
* The highest estimated maximum swimming speeds were found in sailfish (8.3±1.4 m s−1), followed by barracuda (6.2±1.0 m s−1), little tunny (5.6±0.2 m s−1) and dorado (4.0±0.9 m s−1); although size-corrected performance was highest in little tunny and lowest in sailfish.
* Contrary to previously reported estimates, the results suggest that sailfish are incapable of exceeding swimming speeds of 10-15 m s−1, which corresponds to the speed at which cavitation is predicted to occur, with destructive consequences for fin tissues.
PDF available.
Reference:
Svendsen, M. B. S. et al. (2016). Maximum swimming speeds of sailfish and three other large marine predatory fish species based on muscle contraction time and stride length: a myth revisited. Biology Open, 5: 1415-1419
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Trends in shore-based angling effort determined from aerial surveys: a case study from KwaZulu-Natal, South Africa
* Understanding the spatiotemporal characteristics of effort is a critical component of managing fisheries.
* Recreational shore-angling is the largest sector of the linefishery and one of the primary recreational activities undertaken along the coast of KwaZulu-Natal (KZN), South Africa.
* The aim of this study was to make a reliable estimate of current total shore-based angling effort in KZN and to examine the spatial and temporal distribution of the effort.
* To do this, randomised monthly flights to count shore-anglers in an ‘instantaneous’ manner were conducted along the entire KZN coastline between January and December 2018, and then compared with similar aerial surveys conducted in 1994/95 and 2007/08.
* A total of 44 flights were undertaken, with 21 and 23 flights conducted along the north and south coasts, respectively.
* Ground-truthing revealed that the aerial counts of shore-anglers were 89% accurate.
* Angler effort was significantly higher over weekends and during good-weather days.
* Seasonality of shore-based angling effort showed that greatest effort occurred during the winter months (June to September), coinciding with the seasonal availability of popular angling species.
* More-developed stretches of the KZN coast with higher population densities and easier beach-access had the highest angling effort.
* Total annual angler effort was calculated to be 785 538 angler-days y–1, which represents a 22.9% decline from the estimate made in 1994/95 and a 6.9% decline from the estimate made in 2007/08.
* Spatial distribution of shore-based fishing effort was very similar in 2007/08 and 2018, with the major differences being a decrease in fishing effort at St Lucia and Maphelane, and a slight increase in effort on the ‘upper’ (northern) south coast during 2018.
* Based on the results of this study, recommendations for improved management of the KZN shore fishery include:
(i) follow-up using an independent roving-creel survey;
(ii) improvement of coastal law enforcement;
(iii) implementation of a linefish observer programme; and
(iv) a repeat of the aerial survey every 10 years.
pdf available.
Reference:Mann, B. Q. & J. B. Mann-Lang (2020). Trends in shore-based angling effort determined from aerial surveys: a case study from KwaZulu-Natal, South Africa. African Journal of Marine Science, 42 (3): 269-281.
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good day,
I need some information, i am going to tugela mouth on the 23/12/24 -29/12/24, to do some drop shot and surf fishing.
what baits to use and what the best time to do fishing, what species :yellow: to target.
thank you
kind regards
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:welc: :toppie: