New research has shown that dolphins offshore of Western Australia's Pilbara coast are following fishing trawlers to feed on injured or discarded fish.

Researchers found that the offshore dolphin population in the area of the Pilbara Trawl Fishery is smaller than previously thought and that some dolphins are faithful to following fishing trawlers over days, weeks and years.

The population size estimate, based on an aerial survey, suggests that between 2,000 and 5,000 bottlenose dolphins use the area trawled by the commercial fishery off WA's Pilbara coast.

Dr Simon Allen, lead author of the study, completed the research as part of his PhD at Murdoch University and said it had important implications for fisheries management.

"Previous studies have shown that 20-50 dolphins are accidentally caught in this fishery every year, and that this population is isolated from coastal bottlenose dolphin populations," said Dr Allen, now Adjunct Research Fellow at the University of Western Australia's School of Biological Sciences.

"Large numbers of dolphins are seen following trawlers, leading to the impression that the population is large but this research shows that the same dolphins stay with trawlers and that this can occur again and again over several years.

"With a smaller dolphin population than expected, these new findings should be used to assess the population's conservation status.

"The tendency for the dolphins to exploit the trawlers as a risky but efficient means of scoring a meal on a repeated basis is problematic for fisheries management, as dolphin foraging "traditions" tend to be handed down from one generation to the next.

"As long as the trawlers are fishing, the dolphins will be there, taking big risks for a cheap meal."

Professor Neil Loneragan, senior author and Professor of Marine Ecology and Conservation at Murdoch University, said the data were preliminary, but critical.

"This research provides the much needed basis for assessment of the level of impact that dolphin capture has on the population," Professor Loneragan said.

The research could inform fisheries and wildlife management agencies assessing the impact of fisheries-related mortality on dolphins and other protected and endangered species.

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More information: Simon J. Allen et al. Preliminary estimates of the abundance and fidelity of dolphins associating with a demersal trawl fishery, Scientific Reports (2017). Journal information: Scientific Reports Simon J. Allen et al. Preliminary estimates of the abundance and fidelity of dolphins associating with a demersal trawl fishery,(2017). DOI: 10.1038/s41598-017-05189-0