ANCHORAGE, Alaska – Sperm whales in the Gulf of Alaska are likely using the sounds of fishing boat engines as underwater dinner bells to hone in on longlines hung with valuable sablefish, scientists said.
The engines make loud, erratic bubbling noises as fishermen maneuver their boats while winching up hundreds of bottom-dwelling sablefish.
The study has helped researchers devise low-cost ways for fishermen to hoodwink the highly intelligent cetaceans.
It estimates there are 90 male sperm whales feeding from longlines in the eastern Gulf of Alaska, part of the world's largest sablefish fishery.
Scientists found the sperm whales tend to feed on longlines in the late spring through summer, during the height of the sablefish season. The season starts in March and ends in November.
Sound receivers attached to the longlines recorded the loud clicks of chattering whales. Scientists used the recordings to gauge how deep the whales were diving and their proximity to the boats.
They found that whales dive shallower than normal when near fishing boats.
Thode and Straley's suggestions for fishermen include fishing earlier or later in the season, hauling in the line without shutting down the engine, 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," said Steve Fish of Sitka, who has fished for sablefish in the gulf for 27 years.
Sperm whales in the gulf have been plucking small amounts of sablefish off the 1-3 mile longlines for at least two decades, sometimes leaving lips and or partly chewed bodies dangling from the hooks.
No one knows how many of the trendy, gourmet fish have been snatched by the snacking leviathans. Fishermen and fisheries managers say the overall economic loss to the 410-boat sablefish fleet is probably low, but has increased in the last decade.
"A couple of times they completely cleaned us out, but usually they take just a few," Fish said.
"It's really a hard thing to get a handle on," said Tory O'Connell, a biologist for the state's Department of Fish and Game. "You don't really know what's come off the gear."
They fear the problem could intensify as the endangered marine mammals increase in number and teach each other the techniques of sablefish snatching. Once a prime target of whalers, scientists suspect sperm whales are recovering in oceans worldwide.
"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."
Sperm whales and other toothed whales, such as pilot whales, cherry-pick fish catches all over the world. Killer whales in the Bering Sea also plunder sablefish longlines.
"The conflict between humans and whales in fisheries will likely increase," Thode said.
As the study continues, scientists will try to record video of the whales feeding off the longline, test different types of longlines and fit the lines with acoustic reflectors to confuse the whales, who use the echoes of their high-pitched clicks to locate undersea objects.
They will also poll fishermen this season to see whether changes in engine handling and gear are fooling the whales.
The North Pacific Research Board is funding the study.
Fishermen in the eastern Gulf of Alaska hauled in about 12.8 million pounds of sablefish last year, according to the National Marine Fisheries Service. Prices at the dock were high, ranging from $3 to more than $4 a pound, O'Connell said.
Epicures in Japan have long coveted the sweet, flakey sablefish, also listed on U.S. menus as butterfish or black cod.
Long popular in Hawaii, gourmands elsewhere in the U.S. have discovered it too: Bon Appetit magazine rated sablefish one of its Top-10 "It-gredients" of the year in 2005.