Trawlers killing Pilbara’s bottlenose dolphins at ‘unsustainable rates’

Up to 60 of Western Australia’s protected bottlenose dolphins a year could be dying trapped in Pilbara trawling nets, which scientists fear will result in a 50 per cent population decline.

The study, published in the by an international team of researchers, is focused on the Pilbara Fish Trawl Interim Managed Fishery, whose two trawlers supply up to 40 per cent of WA’s market, targeting emperor, snapper, trevally, cod and grouper.

The Department of Agriculture, Water and the Environment late last year found that relatively large numbers of dolphins, 11 to 17, were being killed within the fishery per year.

But the peer-reviewed study has suggested that independent fishery observers estimated at one point bycatch deaths were between 45 and 60 dolphins per year.

Modelling found that if just 50 dolphins were killed each year in trawl nets, the population would decline by 50 per cent over the next 100 years.

Research Fellow at The University of Western Australia and Senior Lecturer at the University of Bristol Dr Simon Allen, who contributed to the research, said there had been some monitoring of bycatch since 2006, but no study into the number of dolphin deaths was ever carried out.

We set out to model different levels of dolphin capture, including those reported in fishers’ logbooks and those reported by independent observers, he said.

Our results show clearly that even the lowest reported annual dolphin capture rates are not sustainable.

He said turtles and sea snakes, as well as a variety of threatened sharks, rays and critically endangered sawfish were also unintentionally caught, including the critically endangered green sawfish.

The study’s lead author Dr Oliver Manlik, an assistant professor at the United Arab Emirates University, said the type of modelling used, a new approach incorporating chance events, showed current dolphin bycatch was 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 because these environmental fluctuations are becoming more frequent and intense with climate change, he said.

WA Fishing Industry Council chief executive officer Darryl Hockey said concerns had been raised about the study using old data sets and being loaded with assumptions.

This report is based on an untested model which utilises old datasets and is loaded with assumptions that could bias the outcomes, he said.

The data used is based on a point in time from around 15 years ago and doesn’t reflect the current situation, reporting requirements, fishing practices and a reduction in the number of commercial fishing vessels in the region.

Hockey said there was a range of other factors impacting the dolphin population, particularly mining, and that commercial fishing had a minimal impact in comparison.

The Department of Primary Industries and Regional Development aquatic resource management director Nathan Harrison said the level and type of interactions with protected species was reported in compulsory logbooks.

Industry and researchers have invested heavily over the past 20 years. . . to reduce interactions with wildlife such as dolphins. This has included adopting bycatch reduction devices on fishing gear, modifying fishing practices and establishing an Industry Code of Practice, he said.

Since 2009, improvements in fishing practices focused on trawl net stability, such as eliminating sharp turns during trawling and hauling, and monitoring otter board performance using sensors, have reduced dolphin mortalities by a further 20 to 59 per cent.

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