Bycatch is the name given by the fishing industry to fish or other marine species caught incidentally while pursuing specific species, sexes or sizes of animals. Because bycatch can result in the accidental death of unwanted creatures, this is one of the ways human fishing can threaten both protected and endangered species. These can include marine life forms like dolphins, seals, sharks, rays and turtles.
Marine biologist Dr Simon Allen from the University of Bristol said: “Bycatch and discards of marine wildlife in commercial fisheries are major challenges for biodiversity conservation and fisheries management worldwide. .
In their new study, Dr Allen and colleagues set out to assess the performance of measures to reduce bycatch implemented by a trawl fishery in Australia.
They used a new method they designed to assess at what level incidental wildlife mortality related to fishing could be considered sustainable in the long term.
Their research focused on dolphins, five of the 41 species of which are already considered endangered.
Dr Allen said: ‘Bycatch reduction devices were placed in Western Australian trawls in 2006, but no quantitative assessment of the impact has been carried out.
“We set out to model different levels of dolphin capture, including those reported in captains’ logbooks and those of independent observers.
“Unfortunately, our results clearly show that even the lowest reported annual dolphin catch rates are not sustainable.”
The paper’s author and evolutionary ecologist, Professor Oliver Manlik of the United Arab Emirates University, added: “We are introducing a novel approach to assess human-induced mortality of wildlife that may be applied to fishing by-catch, hunting, lethal control measures or wind turbine strikes.
“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, such as heat waves.
He added: “These environmental fluctuations are becoming more frequent and intense with climate change.”
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Australia’s fisheries are probably not alone in failing to tackle bycatch and threatening to wipe out endangered species.
The EU – whose inland and offshore fishing fleets total nearly 100,000 vessels – and the UK employ only voluntary or low levels of fisheries monitoring and have no quantitative conservation targets.
Given this, said Dr Allen, the EU and UK are failing to address the bycatch problem in any meaningful way.
The team added: “Greater transparency and the application of more rigorous methods would improve the scientific basis for decision-making regarding the impacts of fishing on non-target species such as dolphins, whales, seals and sea birds.”
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Among the researchers was evolutionary biologist Dr Robert Lacy of the Species Conservation Toolkit Initiative.
This program – which is a collaboration between the Conservation Planning Specialist Group, the Chicago Zoological Society and the Smithsonian Conservation Biology Institute – aims to promote the development and global availability of effective tools for species risk assessment, conservation and population management.
The team plans to make its new method for assessing the impacts of fishing – which it has dubbed “Sustained Anthropogenic Mortality in Stochastic Environments” (SAMSE) – readily available to researchers and wildlife managers around the world.
The full results of the study have been published in the journal Conservation Biology.