Science corner: latest fish & fisheries research

[John F]

That's very rapid growth 

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!

[John F]

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.

[FishStyx]

"1 080 mm fork length" 


Good for the MPAs... Now we just need to enforce them better... For EVERYONE.

[John F]

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.
 

[REEFMAN]

Thats incredible! Expelled a steel spike from it's stomach, out through it's skin!! 

[soupcan]

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!

[John F]

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.

[FishStyx]

Fascinating that it could actually find it's way through the stomach lining.

[John F]

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.

[Visenvryheid]

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
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/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


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?

[Visenvryheid]

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.

[John F]

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

[REEFMAN]

R26 Billion! 

[FishStyx]

I made a fair contribution but not quite R26bn.

[John F]

First known 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.

[CRANKMAN]

Note to the Transkei anglers... try sliding some broccoli on your next outing   

[sardinella]

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.

[tkei]

Note to the Transkei anglers... try sliding some broccoli on your next outing 

depends on how much transkei gold you found before you go fishing

[FishStyx]

Note to the Transkei anglers... try sliding some broccoli on your next outing 

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 


... Apologies for going off topic Marcos 

[John F]

The largest aggregation of giant trevally Caranx ignobilis (Carangidae) on record

    

* 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.