Almost 90 Percent Of Dolphin Population Killed Off By Overfishing
Overfishing has been blamed for an "alarming" drop in dolphin numbers, with fears their populations may be at just 13 per cent of what they were in 1980.
An international group of scientists -- including from Queensland's James Cook University -- used the numbers of dolphins caught accidentally in fishing nets as a way to estimate the wider population present in the world's oceans.
Tens of thousands of dolphins are snared in nets each year.
The researchers found the numbers of dolphins snared had decreased by one-fifth since 2004, a sign of a rapid decrease in the number of dolphins in the ocean.
"The declining cetacean bycatch rates shown by what we can measure suggest current mortality rates are not sustainable," said James Cook University’s Dr Putu Mustika, one of the researchers involved in the project.
"The estimates we have developed show that average small cetacean abundance may currently be 13 percent of the 1980 levels."
Mustika said the decreasing numbers caught in nets came as fishing operations had increased.
She pointed to a rise in the use of gillnets, which are huge rectangular nets set up as vertical walls in the ocean and currently banned by the United Nations -- but still used widely by fishing companies in some countries.
They can be up to 30 kilometres long, and run 20 metres deep into the ocean.
While a boost in the deployment of gillnets would normally be expected to snare more dolphins, researchers concluded that the small decrease in dolphin captures pointed to a much larger decrease in their overall population.
"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,” Mustika said.
More than four million small ceteceans -- including whales, dolphins and porpoises -- were caught in Indian Ocean fishing operations between 1950 and 2018, according to official data from fisheries. Mustika said some of this data "may be unreliable" but was valid enough to allow a "credible" estimate of the dolphin populations.
Mustika said the use of gillnets was a concern and called for greater monitoring and governance of fishing practises, to help dolphin numbers to grow.
"Cetacean bycatch in Indian Ocean tuna gillnet fisheries has been a concern for decades but has been poorly studied, reflecting the political reality that hundreds of thousands of relatively poor fishermen and their families rely on gillnet fisheries,” she said.
In 2018, WWF Australia and the Australian Marine Conservation Society published an investigation claiming more than 60 dolphins and 60 dugongs were caught each year in gillnet fishing on Queensland’s east coast -- far higher than official numbers reported by fisheries.
Reports found several dugongs had died from "dry drowning" after being caught in the nets.
“Gillnets can and do kill threatened species like snubfin dolphins and dugongs. Our vulnerable species need sanctuary. We must permanently remove gillnets from their habitats,” said AMCS campaigns manager Tooni Mahto.
At the time, she called for "urgent, drastic changes" in fisheries to protect dolphin populations.