Arctic Science Journeys
How Orcas Hunt
STORY: A few yards off the bow of Craig Matkin's small skiff, the surface of the water begins to ripple, and then erupts into foam and spray. A porpoise breaks the surface, and just as suddenly is pulled back into the water. Matkin is witness to what few people will ever see: a killer whale making a kill.
"Occasionally, you get these surface chases and Dall's porpoises being flipped up into the air, this kind of stuff. One of the things that happened on this last trip is I was able to watch a group of five killer whales and they traded off chasing this Dall's porpoise. Once they got it separated, there was a chase. Four or five killer whales were lazing around at the surface like nothing was happening, while one of them was in hot pursuit, leaping, and aerial activity when they got to the surface of the water. And I saw at least one trade off where one animal would come in and the one that had been chasing quit. The whole thing took about five minutes--it was pretty drawn out."
Matkin is a biologist with the North Gulf Oceanic Society. He's spent the last dozen years studying killer whales in Prince William Sound. The whales he's watching on this day belong to a group scientists call AT-1. While some other groups of whales in the sound prey exclusively on fish, these orcas eat seals and porpoises. Matkin says the AT-1's hunting strategy hinges on the group's highly developed social structure.
"Now the marine mammal eating types, it's a whole different program. They do hunt in groups, coordinated groups, where they're obviously in communication. Also, each animal contributes to finding prey. When they're really in hunting mode, they move very quietly on the surface or below the water."
While killer whales use stealth to sneak up on prey, they also have developed ways to communicate and coordinate their attacks. Eva Saulitis is a biologist who first recorded unique vocalizations killer whales make while hunting. She calls the sounds "quiet calls."
"They're very quiet, very soft, low amplitude and lower frequency than loud calls. So I think what they're using them for is to stay in communication with each other while they're hunting, but to have sounds that their prey won't detect, because the way that they hunt is mainly by stealth and passive listening. They listen to sounds their prey make."
And, once a kill is made, the whales share in the feast, albeit some share more than others. Craig Matkin:
"And then we've also watched this last trip a couple times this prey sharing which goes on afterwards. We've noticed that sometimes the animal that makes the kill, if it's off away from the others, it wolfs down a bit of it before they share. But there's definite prey sharing."
Prince William Sound is home to about 300 killer whales. Most belong to groups that live in the sound year-round. These are called resident whales. The orcas of AT-1 however, are only regular visitors to the sound. Their travels throughout the year take them into the Gulf of Alaska, to places scientists have not yet been able to follow. For Arctic Science Journeys, this is Debra Damron.
Arctic Science Journeys is a radio service highlighting science, culture, and the environment of the circumpolar north. Produced by the Alaska Sea Grant College Program and the University of Alaska Fairbanks.
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