An international team of researchers has warned the accidental capture of dolphins by boats using trawl fishing methods will have an unsustainable impact on dolphin populations.
- A new study says the accidental capture of dolphins by fishing trawlers is unsustainable
- Researchers looked at a Pilbara trawl fishery and found protected species were invariably caught up
- The study concluded even the lower end of reported dolphin capture numbers is too high for the population to withstand
The study looked at a trawl fishery in the Pilbara and the unintended netting, or bycatch, of dolphins.
Despite trawl nets being fitted with devices designed to reduce bycatch since 2006, the study concluded that even the lowest recorded capture rate of dolphins was too high.
Professor Neil Loneragan of Murdoch University said estimates from skippers and independent observers show between 16 and 25 dolphins were caught in the nets every year in the Pilbara fishery.
“Most people would think that’s not going to be significant, but you’ve got to take into account that the dolphins only produce one or two young, and they will have the calf for three years,” he said.
“They’re only producing young [at the most] every three years once they mature, so removing animals can have quite an impact.”
Senior lecturer at the University of Bristol, Simon Allen, said the team analysed the impact on the population based on different bycatch rates.
“We set out to model different levels of dolphin capture, including those reported in fishers’ logbooks and those reported by independent observers. Unfortunately, our results show clearly that even the lowest reported annual dolphin capture rates are not sustainable,” Dr Allen said.
The study’s lead author Oliver Manlik from the United Arab Emirates University said even the lowest estimates of dolphin bycatch were “unsustainable”.
“This not only raises concerns for the dolphin population but highlights a problem with other assessments that don’t account for random events, like heatwaves,” Dr Manlik said.
Dolphins are not the only unintended casualties, according to senior lecturer at the University of Bristol, Simon Allen.
“The Pilbara Fish Trawl Interim Managed Fishery targets emperor, snapper, trevally, cod and grouper,” Dr Allen said.
“However, this also results in the capture of protected species including dolphins, turtles, and sea snakes, as well as a variety of threatened sharks, rays, and critically endangered sawfish.”
An ecological risk assessment of the Pilbara Fish Trawl Interim Managed Fishery, looking at the impact on target and non-target species, is due to be published later this year.
The team of researchers hoped their new model for assessing the sustainable limits of wildlife mortality, which they used in their study, could be implemented more broadly.
“We hope that this approach will be incorporated in the assessment of the fishery by the Department of Primary Industries and Regional Development in their ecological assessments,” Professor Loneragan said.
“Currently we don’t see a quantitative approach used in assessing the dolphin bycatch, and this model [developed by the team of researchers] provides a mechanism for doing that, as well as assessing potentially the impact on other species.”