Science corner: latest fish & fisheries research

[John F]

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.

[icstuff]

Thank you john if only I could read...

[John F]

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.

[John F]

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

[ST(d)]

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.

[John F]

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.

[John F]

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) or PM me.


Reference
Mann, B. (ed) (2013). Southern African marine linefish species profiles. ORI Special Publication, 9: 343pp. 

[John F]

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.

[REEFMAN]

* 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!

[John F]

I thought that would catch the interest of many! Yeap, interesting how things turn out, hey?

[WalkersKiller]

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.

[John F]

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

[WalkersKiller]

  I have a photo of a pregnant fm Blue Ray, DW 90cm...

[John F]

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.

[John F]

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.

[Seventenths]

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

[John F]

According to the paper they only used one type of grip (no brand mentioned).

This is what they used

[Seventenths]

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!

[John F]

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.

[John F]

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.