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SOURCE: Science

DATE: December 11, 2019

SNIP: More than a dozen species of small whales and dolphins are headed toward extinction, a new study finds. The main reason: modern fishing nets, which trap and kill hundreds of thousands of the animals every year.

The findings are “a good summary of the insidious threats facing critically endangered populations of dolphins and porpoises around the world,” says C. Scott Baker, a conservation geneticist and cetacean expert at Oregon State University in Newport who was not involved with the study.

Small cetaceans such as the vaquita and various river dolphins successfully lived alongside human fishers for thousands of years in coastal waters, estuaries, and rivers. Then, after World War II, fishers began to replace their cotton and hemp nets with less expensive and more durable synthetic ones. These so-called gillnets don’t require expensive equipment or large vessels, making them especially attractive to small-scale fishers worldwide. But cetaceans (as well as other marine mammals and sea turtles) can’t bite through the nets if caught in them, as they could with the cotton nets.

Conservationists have tried for at least 30 years to develop nets that the animals can avoid or easily escape, but they have yet to come up with a good solution. They have also urged governments to enact strict regulations and outright bans on the use of gillnets, but these are typically difficult to enforce.

Now, 13 small cetacean species are nearing extinction primarily because of these nets, marine biologists report this month in Endangered Species Research. Using data collected by fishing authorities who have recorded population sizes, trends, and the rates at which cetaceans are caught up in nets meant for fish, the team finds that China’s baiji river dolphin is “almost certainly extinct”; Mexico’s vaquita porpoise, which numbers fewer than 19, is “on the very brink of extinction”; and long-term prospects for West Africa’s Atlantic humpback dolphin are “grim.” The outlook is also poor for a subspecies of the Māui dolphin found only off the southwest coast of New Zealand’s North Island, as well as for the Taiwanese humpback dolphin, the Yangtze finless porpoise, three species of Asian river dolphins, and the Baltic Sea harbor porpoise. In each case, gillnets were the biggest threat.

Many of these species will vanish unless gillnets are eliminated, says Robin Baird, a marine biologist and cetacean expert with Cascadia Research Collective in Olympia who was not involved with the study. But that will take “political courage,” he stresses, because governments will have to make unpopular decisions, such as enacting no-fishing conservation zones and enforcing strict bans. Unfortunately, he says, at this point that is the only way “to keep these species and populations from going extinct.”