New research shows 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. Boat-based research also indicates that some dolphins repeatedly followed the trawlers around, day in, day out, feeding on injured or discarded fish.
Lead author of the study, Dr. Simon Allen, now at The University of Western Australia, 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,” Dr Allen said.
“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 was 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.
The study can be found here
David Stacey (UWA Media and Public Relations Manager) (+61 8) 6488 3229 / (+61 4) 32 637 716
Dr Simon Allen (UWA School of Biological Sciences) (+61 4) 16 083 653
Professor Neil Loneragan (Murdoch University) (+61 4) 19 950 034