Science corner: latest fish & fisheries research

[John F]

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.

[WalkersKiller]

Very, very interesting...

[John F]

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.

[John F]

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.

[John F]

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.

[REEFMAN]

Didn't like the last one.  Makes me sick 

[John F]

Yeah humans are not giving them much room to thrive .... eat the adults, poison the babies, eish...

[WalkersKiller]

Extremely interesting and insightful bru 

[John F]

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.

[WalkersKiller]

Very interesting Marcos 

[John F]

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.

[WalkersKiller]

Very interesting...

[Marthin]

That last GW study has been pretty harshly criticized by other researchers....

[John F]

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... 

[Marthin]

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.)

[WalkersKiller]

Very, very interesting!

[John F]

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...   

[John F]

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.

[John F]

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.

[REEFMAN]

So some Bream species become hesitant about feeding on baited hooks?! Learned response?