PUBLISHED: 6:05 PM on Wednesday, October 8, 2008
Scientists studying offshore orcas
Scientists at NOAA's Alaska Fisheries Science Center are fastening down facts on the most elusive of killer whale eco-types - called offshore killer whales - which are known to range from Alaska to California.

"We don't know if they are an open-ocean population or a continental shelf population," said Doug DeMaster, Director of the Alaska Fisheries Science Center. "But we do know that offshore killer whales can move great distances over a relatively short period of time. "

The offshore killer whales are genetically different from their kin, the marine mammal-eating transient killer whales and fish-eating resident killer whales.

"Offshore killer whales differ in size, shape and behavior from other two killer whales eco-types," said Marilyn Dahlheim, a researcher from the Alaska Fisheries Science Center. Offshore killer whales are shyer, moving evasively and unpredictably when approach by boats, she explained. They are smaller and they tend to live in larger groups - up to 75 or 100 individuals.

Although the ranges of the three eco-types occasionally overlap, offshore killer whales have never been seen to intermix with resident or transient killer whales.

Offshore killer whales most likely subsist on fish. They have, for instance, been seen with salmon in their mouths. Scientists have observed many other foraging behaviors which also support the idea that they are fish-eaters. Scientists have watched offshore killer whales in the company of sea lions, gray whales, fin whales and dolphins. In no case did the offshore killer whales target these animals as prey, nor did the other marine mammals act as if the offshore killer whales were a predatory threat.

In recent years, researchers, using photographs of individual whales, have found 57 matched sightings of offshore killer whales between Alaska and Washington, six matches between Alaska and Oregon and 81 matches between Alaska and California. Of these, 46 individual whales were seen in all three places: Alaska, Washington and California.