Fishing could wipe out dolphins

The number of Hector’s Dolphins caught in commercial gillnets is above 10 times sustainable levels, according to a new analysis by Otago University’s Associate Professors Liz Slooten and Steve Dawson.

Their study used the Potential Biological Removal (PBR) method, developed by the US National Marine Fisheries Service. This is a commonly used standard for determining a level of human impact on marine mammal populations which, if exceeded, is likely to cause population decline.

The results of this analysis are consistent with population viability analyses carried out by scientists from NIWA, the fishing industry and the University of Otago. Associate Professor Slooten says this means the death toll exceeds sustainable impact by more than 10 times.

“It is highly significant that all of these analyses indicate that Hector’s dolphin populations are declining so rapidly,” says Associate Professor Slooten.

If the recent level of bycatch were to continue, says Associate Professor Slooten, Hector’s dolphins are expected to decline to around 5,000 individuals over the next 50 years.

“On the other hand, if they were protected from fisheries mortality throughout their range they could recover to some 15,000 individuals over that same time,” she says.

Hector’s dolphins are of particular significance, as they are only found in New Zealand. The main threat to the species is entanglement in fishing gear, in particular gillnets.

NIWA estimate that 110-150 Hector’s dolphins have been killed each year during 2000-2006. Hector’s dolphin populations have been seriously depleted as a result of fishing, to less than a third of original population size, with the North Island population worst affected at less than 10 percent of its original size.

The new analysis is the most recent addition to a large body of scientific data, published in the peer-reviewed scientific literature, including New Zealand and international journals. Several international scientific agencies (including the Society for Marine Mammalogy, Scientific Committee of the International Whaling Commission and IUCN) have pointed out that there is ample evidence on which to base effective protection measures for Hector’s dolphin.

“It’s important to emphasise that the PBR for Hector’s dolphins is a maximum level of total human impact which, if exceeded, would likely cause further population depletion. Fisheries mortality needs to be kept well below these levels, given that there are other human impacts on the species – including pollution, marine mining and proposed tidal energy generation,” according to Associate Professor Slooten.

She recommends that dolphins be protected from fisheries mortality by changing to more selective, sustainable fishing methods.

“This would have benefits not only for Hector’s dolphin conservation but also for other dolphin species and seabirds caught in these fisheries, and in the long term for the fishing industry itself,” she says.

The Minister of Fisheries, Jim Anderton announced new protection measures in May this year, which were to be enacted on 1 October. These protection measures are a long way from total protection and likely to slow rather than halt population declines. The proposal resulted from a two-year consultation process with the fishing industry and other stakeholders, including recreational fishers, iwi, conservation groups and government departments.

“Just two weeks before the 1 October deadline, the fishing industry took the Minister to Court. This means that dolphin protection has been delayed again, this time by a court case and an election,” says Associate Professor Slooten.

Source: Science Alert