ANCHORAGE, Alaska (AP) -- Years ago, the sound of a boat sometimes spelled death for the heavily hunted sperm whale. Now, some of them have figured out, it means dinner.
Scientists recently realized that sperm whales in the Gulf of Alaska zero in on boat engines to locate miles of fishing lines hung with valuable sablefish.
"That's the whales' cue," said Jan Straley, an assistant professor at the University of Alaska Southeast who since 2002 has helped lead the study.
Sperm whales don't tune in to just any engine noise to track what are essentially miles of sablefish shish kebabs. The endangered whales key in on the engines' sporadic bubbling as fishermen turn them on and off while hauling in longlines, the ongoing study said.
The work has led researchers to recommend some low-cost ways for fishermen to hoodwink the highly intelligent cetaceans.
The researchers estimate there are 90 male sperm whales feeding from longlines in the eastern Gulf of Alaska, part of the world's largest sablefish fishery.
The sweet, flaky flesh of the sablefish, long prized in Japan and Hawaii, is gaining popularity in the mainland United States, where it is listed on menus as butterfish or black cod. About 12.8 million pounds (5.8 million kilograms) of sablefish were hauled in last year from the eastern gulf, with dock prices that sometimes topped US$4 a pound (euro7.50 a kilo). Consumers pay $18.99 a pound (euro35.40 a kilo) for the fish at the upscale Fresh Direct food delivery service in New York.
Scientists found the sperm whales tend to feed on longlines in the late spring through summer, during the height of the sablefish season.
Sound receivers attached to the longlines recorded the loud clicks of chattering whales. Using the recordings, scientists found that whales dive shallower than normal when near boats hauling up the bottom-dwelling sablefish.
"The whale doesn't have to dive as deep to get its food," said Aaron Thode, an associate researcher at the University of California, San Diego, who is also leading the study, which is funded by the federally established North Pacific Research Board.
Sperm whales in the gulf have been plucking sablefish off the longlines -- which are up to 3 miles (5 kilometers) long -- for at least two decades. They also take halibut and, in one instance, lingcod.
Killer whales in the Bering Sea and Prince William Sound also plunder sablefish longlines. Sperm whales and other toothed whales, such as pilot whales, cherry-pick fish catches all over the world.
No one knows how many of the trendy gourmet sablefish have been snatched by the snacking leviathans. Fishermen and fisheries managers say the overall economic loss to the gulf's 410-boat sablefish fleet is probably low, but has increased in the past decade.
"A couple of times they completely cleaned us out, but usually they take just a few," said Steve Fish of Sitka, who has fished for sablefish in the gulf for 27 years.
Fishermen fear the problem could intensify as the endangered marine mammals increase in number and teach each other the techniques of sablefish rustling. Once a prime target of whalers, scientists suspect sperm whales are recovering in oceans worldwide, although there are no definitive population numbers.
"You didn't used to see them at all in the gulf, but they started showing up in the late '80s, early '90s," Fish said. "Now you can hardly make a trip without seeing sperm whales."
Thode and Straley's suggestions for fishermen include fishing earlier or later in the season, hauling in the line without changing engine speed, or making decoy noises with the engine to draw whales to a different area.
Fishermen said they will try the methods this season, but many believe the large-brained whales are just too smart.
"We try to get creative, but there's only so much you can do," Fish said.