Bitten and shredded sablefish caught in the Gulf of Alaska.  This is evidence of sperm whale depredation on longline gear.

The earliest record of possible depredation is a reference to a sperm whale caught in 1904 off Shetland with fishhooks in its stomach.  Today, sperm whales associate with fishing operations in a number of locations around the globe, particularly longline operations, but also with trawl operations. 

Interactions between sperm whales and longline fisheries have been well-documented in the Southern Ocean - in particular off South Georgia, the Kerguelen Islands, and Southern Chile.  Such interactions include entanglement in gear, following vessels for days, and observed feeding off gear.  This evidence, combined with anecdotal reports, suggests that interactions between sperm whales and longline operations may be widespread in Southern Ocean waters. In the Gulf of Alaska, sperm whale depredation of longline gear set for sablefish has occurred since at least 1978, though, aside from scattered anecdotal reports few data are available regarding such behavior in relation to commercial longline operations.

Sperm whale diving near longline vessel in the Gulf of Alaska.  Note the fresh wounds on the tail stalk below the flukes possibly made by interacting with fishing gear. Photo by Eric Coonradt.

Until the early 1980s, the sablefish fishery was year round.  An increase in the number of fishing vessels, however, resulted in a shortened season.  In 1994, the entire quota was caught in two weeks.  In 1995, the management strategy changed to a quota system, where the annual quota is divided among license holders and each may fish from March to November until his quota is met.  

Due to the change in the fishing regulations that permits a longer season, the number of sperm whale encounters with longlines has increased substantially. Whales can sometimes strip up to 20% of the fish off any given longline deployment.  A domestic sablefish survey in the Gulf of Alaska, looked at catch rates from 1999 to 2001 for all sets with sperm whales present.  They compared boats with and without evidence of depredation and found a 23% lower catch rate in boats with depredation.

Sperm whale - longline interactions worldwide.

During fall 2002, Alaska-based researchers Jan Straley (PI) and Greg Beam (key associate) traveled to Samoa to participate in the first technical workshop, “Cetacean interactions with commercial longline fisheries in the South Pacific Region: Approaches to Mitigation.”   This workshop brought together participants from all over the world to discuss depredation interactions by cetaceans upon commercial longline fisheries. Key findings from this workshop underscored the need to work proactively with the fishing fleets, identify key information about cetaceans as well as their interactions with longline gear.  This information is needed in order to develop applied research on mitigation measures.

Halibut depredated by Sperm Whales