Bycatch is the name given by the fishing industry to fish or other marine life that are caught accidentally while going after specific species, sex, or sizes of animal. Because bycatch can result in the accidental death of the unwanted creatures, it is one of the ways that human fishing can threaten both protected and endangered species. These can include such forms of marine life like dolphins, seals, sharks, rays and turtles.
Marine biologist Dr Simon Allen of the University of Bristol said: “Bycatch and discarding of marine wildlife in commercial fisheries are major challenges for biodiversity conservation and fisheries management the world over.”
In their new study, Dr Allen and his colleagues set out to evaluate the performance of measures designed to reduce bycatch implemented by a trawl fishery in Australia.
They used a new method they have devised to assess at what levels accidental fishing-related wildlife mortality could be considered sustainable in the long run.
Their research focused on dolphins, of which five of the 41 species are already considered endangered.
Dr Allen said: “Bycatch Reduction Devices were placed in Western Australian trawl nets in 2006, but no quantitative assessment of the impact was carried out.
“We set out to model different levels of dolphin capture, including those reported in skippers’ logbooks and those by independent observers.
“Unfortunately, our results show clearly that even the lowest reported annual dolphin capture rates are not sustainable.”
Paper author and evolutionary ecologist Professor Oliver Manlik of the United Arab Emirates University added: “We introduce a novel approach to assessing human-caused mortality to wildlife that can be applied to fisheries bycatch, hunting, lethal control measures or wind turbine collisions.
“And when we incorporate stochastic factors — random events — we show that previous methods of assessing wildlife mortality were not conservative enough.
“This raises concerns for the dolphin population and highlights a problem with other assessments that do not account for random events, like heatwaves.
He added: “These environmental fluctuations are becoming more frequent and intense with climate change.”
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Fisheries in Australia are likely not the only ones failing to address bycatch and threatening to make endangered species extinct.
Both the EU — whose domestic and deep-sea fishing fleets total nearly 100,000 vessels — and the UK employ only voluntary or low levels of fisheries monitoring and have no quantitative conservation objectives.
Given this, Dr Allen said, the EU and the UK are failing to meaningfully address the bycatch problem.
The team added: “Greater transparency and the application of more rigorous methods would improve the scientific basis for decision-making around the impacts of fisheries on non-target species like dolphins, whales, seals and seabirds.”
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Among the researchers was evolutionary biologist Dr Robert Lacy of the Species Conservation Toolkit Initiative.
This programme — which is a collaboration between the Conservation Planning Specialist Group, the Chicago Zoological Society and the Smithsonian Conservation Biology Institute — is working to promote the development and global availability of effective tools for species risk assessment, conservation actions and population management.
The team are planning to make their new method for assessing the impacts of fishing — which they have dubbed “Sustainable Anthropogenic Mortality in Stochastic Environments” (SAMSE) — easily available to both researchers and wildlife managers worldwide.
The full findings of the study were published in the journal Conservation Biology.
