Dolphins take ‘risks for cheap meal’
Pilbara dolphins are proving they are smart little risk-takers as new research shows a small section of the offshore mammals’ population are following fishing trawlers for an easy feed.
The University of Western Australia’s Dr Simon Allen, who completed the research as part of his PhD, said some dolphins were faithful, following fishing trawlers over days, weeks and years.
“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,” he 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.”
According to conservation experts, the new research could inform fisheries and wildlife management agencies assessing the impact of fisheries-related mortality on dolphins and other protected and endangered species.
The population size estimate, based on an aerial survey, suggests between 2000 and 5000 bottlenose dolphins use the area trawled by the commercial fishery off WA’s Pilbara coast.
Boat-based research also indicated some dolphins repeatedly followed the trawlers around dayin, day-out, feeding on injured or discarded fish.
“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,” Dr Allen said.
“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,” he said.
Bottlenose dolphins in Shark Bay.