Study indicates alarming fall in dolphin numbers

James Cook University –

A study of how many dolphins are caught in tuna fishing nets estimates the mammals may now be at just 13 per cent of their numbers prior to 1980.

James Cook University’s Dr Putu Mustika was part of an international group that looked at the bycatch from tuna gillnets (including driftnets) in the Indian Ocean. The group was led by Dr Charles Anderson of the Manta Marine organisation in the Maldives.

“We combined results from 10 bycatch sampling programmes between 1981 and 2016 in Australia, Sri Lanka, India and Pakistan to estimate bycatch rates for cetaceans (whales, dolphins and porpoises) across all Indian Ocean tuna gillnet fisheries,” said Dr Mustika.

She said while some of the official data may be unreliable, scientists had been able to come up with a credible picture of the dolphin catch.

Dr Mustika said tuna fishers operating in theIndian Ocean caught about 4.1 million small cetaceans between 1950 and 2018.

“The vast majority of the cetacean bycatch is dolphins. Estimated cetacean bycatch peaked at almost 100,000 a year during 2004−2006, but has declined to 80,000 animals a year, despite an increase in the tuna gillnet fishing effort,” she said.

Dr Mustika said the numbers may be substantially higher as the figures take little or no account of things such as delayed mortality of cetaceans that escape from the nets or mortality associated with ghost nets.


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