ANCHORAGE – Sperm whales in the Gulf of Alaska are likely using the sounds of fishing-boat engines as underwater dinner bells to home in on long lines 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.
“That’s the whales’ cue,” said Jan Straley, a researcher at the University of Alaska Southeast who since 2002 has helped lead an ongoing study of the whales’ behavior. The study has helped scientists devise low-cost ways for fishermen to hoodwink the highly intelligent cetaceans. It estimates there are 90 male sperm whales feeding from long lines in the eastern Gulf of Alaska, part of the world’s largest sablefish fishery.
Scientists found the sperm whales tend to feed on long lines 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.
“The whale doesn’t have to dive as deep to get its food,” said Aaron Thode, a researcher at UC San Diego, who is also leading the study.
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- to 3-mile long lines for at least two decades, sometimes leaving lips 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 past 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.”