'Mmmm...Shark,' Says Killer Whale

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Like a child eating too many jawbreaker candies, some orcas damage their teeth by eating crunchy, abrasive food. But they aren’t eating candy, they are eating sharks.

The orcas (Orcinus orca), or killer whales, in the deep, offshore waters of the northeast Pacific chow down on the sluggish deep-sea Pacific sleeper shark. But dining on shark delicacies comes at a price.

The denticles, tough teeth-like structures embedded in the shark’s skin, grind down the whale’s teeth. Some older whales have been found with their teeth ground down to the gums, according to John Ford of the Pacific Biological Station in Nanaimo, British Columbia, and his team or researchers. Their research was published recently in the journal Aquatic Biology.

“It may be that the young whales have to do most of the work,” Ford told the journal Nature. “The older ones are probably just gumming away at the liver.”

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This research helps ocean scientists solve a mystery of what the “offshore” population of killer whales eats. Killer whales have three distinct groups, “resident” fish-eaters; “transient” mammal-eaters; and “offshore” whales, the most mysterious of the three. Many marine biologist consider the three groups as separate species in need of individualized conservation strategies.

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Because they feed hundreds of feet beneath the surface, “offshore” orca’s diets had been a matter of speculation. Only two feeding events were witnessed between 1988 and 2009

Though the researchers did not directly witness the whales feasting on sharks deep in the briny gloom, they did find chunks of pink shark meat on the surface after observing the whales engaging in feeding behaviors, like quick turns and long deep dives. Genetic analysis confirmed that the meat came from at least 16 Pacific sleeper sharks (Somniosus pacificus).

IMAGE 1: Killer Whale (Orcinus Orca), Vancouver Island, British Columbia, Canada. Credit: Chris Cheadle/All Canada Photos/Corbis.

IMAGE 2: A 30-foot sleeper shark, the largest flesh-eating shark ever photographed, submerges a one-meter bait cage into the ocean floor mud. Credit: Ralph White/Corbis. 

IMAGE 3: Orca body types (Albino.orca; Wikimedia Commons) Type A – Physical description: “Typical” killer whale, a large, black and white form with a medium-sized white eye patch. Habitat and Diet: Open water; feeding mostly on minke whales. Type B – Physical description: Smaller than Type A. It has a large white eye patch. Most of the dark parts of its body are medium gray instead of black, although it has a dark gray patch called a “dorsal cape” stretching back from its forehead to just behind its dorsal fin. The white areas are stained slightly yellow. Diet: Mostly seals. Type C – Physical description: smallest type and lives in larger groups than the others. Its eye patch is distinctively slanted forwards, rather than parallel to the body axis. Like Type B, it is primarily white and medium gray, with a dark gray dorsal cape and yellow-tinged patches. Diet: Antarctic Cod. Type D – Physical description: Extremely small white eye patch, shorter than usual dorsal fin that curves back, and bulbous head. Habitat and Diet: Appears to be circumglobal in subantarctic waters between latitudes 40°S and 60°S. Diet: Unknown; presumed to be fish.