Sperm whales have turned burglar. They have learned to follow commercial fishing boats off the coast of Alaska, and then pick huge volumes of fish from the lines. It now seems they can take about 5% of the fishermen鈥檚 annual quotas.
Sperm whales are the largest toothed predators on Earth. . Lone whales typically harass boats in the eastern Gulf of Alaska. When they attack a boat they work feverishly to pick fish from the hooks, sometimes without damaging the gear or even being seen.
at Sierra Nevada College in Nevada and her colleagues tracked the whales鈥� impact on the Alaskan fishery over 27 years. These fishermen use longlines stretching kilometres along the ocean floor, with thousands of hooks baited with octopus or squid. These are tempting targets.
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The team found that sperm whales can take a quarter of a ship鈥檚 catches in a single attack. They may attack many times an hour.
This translates to a $5-8 million annual loss for Alaska鈥檚 $100-million sablefish industry.
More whale attacks
, according to a 2017 study by Peterson and at the NOAA Alaska Fisheries Science Center. They work in pods of as many as 40, and can take up to half of a catch each time they attack.
This behaviour was first documented in the 1950s, when Japanese whalers in the Bering Sea reported orcas targeting their catches, says Hanselman. 鈥淪perm whales are more of a new issue.鈥�
Hanselman and Peterson say two factors are behind the upswing.
One is the 1986 whale hunting moratorium, as sperm whale numbers have risen 4% a year since. The other is Alaska鈥檚 1995 move from seasonal 10-day fishing bonanzas to individual quotas. The marathon seasons have given both species plenty of opportunity to learn about fishing practices.
Stop the whales
Mariners cannot fight back, as both species are covered by the . Sperm whales are a species 鈥� whereas to assess how threatened they are.
鈥淭here鈥檚 very little that can stop the whales once they鈥檙e there,鈥� says Peterson. So fishermen have tried to keep them away.
鈥淭hey鈥檝e tried decoy buoys, boats fishing close in tandem, they鈥檝e tried making noises,鈥� says Peterson. An attempt to confuse the whales鈥� echolocation with submerged noise-making devices actually worked as a dinner bell, she says.
The 聽identifies whale-free fishing grounds by tracking their movements.
Meanwhile, in Patagonia, where sperm whales and orcas also thieve, and less gear. Shorter lines mean fewer fish to steal.
A better 鈥� albeit pricier 鈥� fix may be to swap out fish hooks for pots with narrow openings. 鈥淪o far, the whales haven鈥檛 figured out how to blast pots open,鈥� says Hanselman. 鈥淏ut it鈥檚 hard to put it past these large-brained mammals.鈥�
Fisheries Research
