(Vancouver Sun)
Orca group wearing down their teeth on abrasive shark diet
BY LARRY PYNN, POSTMEDIA NEWSJANUARY 18, 2011 4:19 AM
Northeast Pacific transient killer whale in Alaska.
Photograph by: Dave Ellifrit/NOAA Alaska Fisheries Science Center/Handout, Reuters files
Marine scientists have discovered a mysterious population of killer whales off the B.C. coast that specialize in killing sharks -- to the detriment of their teeth.
Scientists have long known that resident killer whales -- which stick to specific hunting ranges -- depend on a diet of fish, especially salmon, and that transient killer whales eat marine mammals such as seals and sea lions.
But the diet of offshore killer whales -- first identified on the B.C. coast in 1989 -- has remained largely a mystery due to their wide-ranging and distant movements.
This study, published in the journal Aquatic Biology, proves through DNA evidence that offshore killer whales prey on large Pacific sleeper sharks, whose skin is so abrasive that it is believed to be wearing the whales' teeth flat.
"It's exciting. It's been a detective hunt for so long," said John Ford, lead author of the study and senior research scientist with the federal Pacific Biological Station in Nanaimo.
Other potential prey of offshore killer whales includes salmon shark, blue shark and spiny dogfish, as well as related elasmobranch species such as skates and rays. They may also consume fish such as halibut, meaning their diet could overlap with resident killer whales.
The study documents how offshore orcas preyed on at least 16 Pacific sleeper sharks at B.C.'s Learmonth Bank, in western Dixon Entrance, in May 2008; and Montague Strait in Alaska's Prince William Sound, in June 2009.
The study was co-authored by Graeme Ellis and Michael Wetklo of the Pacific Biological Station, Lance Barrett-Lennard of the Vancouver Aquarium, and Craig Matkin of the Alaska's North Gulf Oceanic Society.
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