Human activities such as commercial fishing often result in the accidental death of non-targeted wildlife, threatening a large number of already endangered species. Many fisheries are not selective and damage marine habitats, while also frequently capturing protected species, like dolphins, seals, sharks, or rays.
A research team led by the University of Bristol and the United Arab Emirates University (UAEU) has now developed a method to assess sustainable levels of human-caused wildlife mortality. When applying this method to a trawl fishery from Australia, the experts have found that dolphin bycatch is unsustainable.
“Bycatch and discarding of marine wildlife in commercial fisheries are major challenges for biodiversity conservation and fisheries management the world over,” said study senior author Simon Allen, a professor of Biology at the University of Bristol.
“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.”
According to study lead author Dr. Oliver Manlik, an assistant professor of Molecular Ecology at UAEU, the novel approach developed together with the University of Bristol is extremely proficient in assessing human-caused mortality to wildlife, and can be applied to fisheries bycatch, hunting, lethal control measures, or even wind turbine collisions.
“And when we incorporate stochastic factors, random events, we show that previous methods of assessing wildlife mortality were not conservative enough,” he said. “This raises concerns for the dolphin population and highlights a problem with other assessments that do not account for random events, like heatwaves, because these environmental fluctuations are becoming more frequent and intense with climate change.”
With only voluntary and low levels of fisheries monitoring and no quantitative conservation objectives, both UK and EU are currently failing to address the significant problems that bycatch entails. Greater transparency and more rigorous methods are needed to improve the scientific basis for decision-making regarding the impact of fisheries on non-targeted species such as dolphins, seals, whales, or seabirds.
The study is published in the journal Conservation Biology.