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AUDIO:Marine mammal researcher John Ford talks to CBC's Quirks & Quarks about killer whales.
Image: The teeth of older whales are often worn flat right to the gum line. (Courtesy of Robin Abernethy/Fisheries and Oceans Canada)

Marine biologists have been mystified by the wear and tear on the teeth of a group of orcas known as offshore killer whales.

While other orcas are known to eat sea mammals and salmon, the diet of this particular group, which travels between southern California and the Aleutian Islands off Alaska, wasn't known. 

John Ford, a marine mammal research scientist with Fisheries and Oceans Canada's Pacific biological station in Nanaimo, B.C., discovered that offshore killer whales have a preference for munching on Pacific sleeper sharks. The whales are often found along the continental shelf of Canada's west coast.

The sharks' skin is extremely abrasive and embedded with rough scales called dermal denticles. Apparently, tearing into these sharks takes a toll on the whale's teeth: in older whales, they are often worn flat right to the gum line, and the tooth's inner pulp is exposed.

However, that does not necessarily mean that older whales are left to starve once they've worn down their teeth to the gums. Ford told CBC's Quirks & Quarks that he thinks younger offshore killer whales might share their kills with their dentally challenged elders.