Science corner: latest fish & fisheries research

[John F]

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.

[Marthin]

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.

[John F]

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   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?!

[John F]

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.

[John F]

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.

[John F]

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.

[REEFMAN]

Fascinating that an adult Grunter travelled 529kms to visit another estuary!

[FishStyx]

the longest durations were spent in the Sundays

I'd also like longer Sundays 

[John F]

the longest durations were spent in the Sundays

I'd also like longer Sundays 

 

[John F]

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.

[FishStyx]

Is there also an increase in jellyfish? I've seen quite a bit of reference to it in the last few years.

[John F]

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


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.



 

[FishStyx]

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


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.

[John F]

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

[FishStyx]

 

[John F]

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.

[John F]

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.

[FishStyx]

That's very rapid growth 

Thanks for these snippets Marcos. I don't always understand everything they say but they are still informative.

[colin]

   Marcos 

[Visenvryheid]

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..