Orcas and Sea Lion Decline
INTRO: In the ongoing debate over what's causing the decline of Alaska's Steller sea lions, researchers have studied everything from nutritional stress to climate change. Now researchers have turned their attention to killer whales. As Doug Schneider reports in this week's Arctic Science Journeys Radio, scientists say the chance to see if killer whales are eating too many sea lions is also a chance to learn more about killer whales themselves.
STORY: Researchers spent last summer combing the coastline of western Alaska, looking for signs that killer whales are feasting on the region's Steller sea lions. While they did observe orcas attacking sea lions, researchers say killer whales probably aren't the main cause of the sea lion's overall population decline. Still, researchers say at least some killer whales seem to prefer the taste of fresh sea lion meat.
Craig Matkin is an independent marine biologist based in Alaska. He says one group of killer whales—a pod he calls the "Kodiak Killers" because they frequent waters around Kodiak Island—is especially skilled at knocking off sea lions.
MATKIN: "My god, the male in that group is an awesome predator. He would go in and take a 350-pound juvenile sea lion and grab it so quickly from the rocks and make short work of them. The kill happens so fast, you don't even know for sure what you've seen until you see the bits of blubber and skin. It's almost like a rain of blubber that comes to the surface."
Matkin has spent more than 20 years studying killer whales in the Prince William Sound region of Southcentral Alaska. Last summer, he joined with state and federal biologists in the first year of a three-year study of killer whales in the western Gulf of Alaska and the Aleutian Islands. The study marks the first time researchers are taking a hard look at killer whales in the region, where sea lion numbers have declined by as much as 80 percent over the past 30 years. Matkin is quick to point out that it's too early to say whether killer whales are to blame for the sea lion decline. But he says all the early signs seem to let them off the hook.
MATKIN: "It's too short a time to make any grand pronouncements. But certainly we haven't found anything in this first year that would push us farther toward thinking that killer whales are the big problem, or were the big problem in the sea lion decline."
Although the study is aimed at understanding the decline of Steller sea lions, Craig Matkin says researchers are learning a lot about killer whales themselves. For example, he says the majority of the orcas seen in western Alaska are what scientists call resident whales. That means they eat only fish. Matkin says researchers saw very few so-called transient killer whales, the kind of orca adapted to prey exclusively on marine mammals.
MATKIN: "These animals genetically are all testing out to be fish-eaters, and our observations indicate the same thing. They're the animals that take the fish off the long-lines. They're the animals that follow the trawlers around and eat the discards. So there are a lot of killer whales out there. That's why people jump to the conclusion that my god, how can these sea lions survive? Well, there are a lot of killer whales but then, there are very few—we're talking about dozens, maybe, in an area like the eastern Aleutians—that are actually eating marine mammals."
Over the summer, Matkin and his colleagues observed and photographed about 460 fish-eating killer whales in the eastern portion of the Aleutian Islands alone. By contrast, he and his team saw only about 23 orcas of the type that hunt sea lions and other marine mammals.
The finding poses interesting questions for researchers. First, how is it that Steller sea lions fare well in places like Southeast Alaska, where there are large numbers of transient killer whales, and do so poorly in the Aleutians, where there are relatively few such orcas? Matkin says only more research will solve the mystery.
MATKIN: "It's pretty ironic that 65 percent of our encounters with transient
killer whales are in Southeast Alaska [while in western Alaska less than
10 percent of encounters are with transients]. Yet the population of both
harbor seals and Steller sea lions is either stable or increasing."
MATKIN: "Taking a small number of Steller sea lions may be an issue in certain areas. Indeed, we calculated that this group of Kodiak Killers could potentially take 400 immature Steller sea lions in the course of a year. That might be an issue."
This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program at the University of Alaska Fairbanks School of Fisheries and Ocean Sciences. I'm Doug Schneider.
Audio version and related websites (above right)
Thanks to the following individual for help preparing this script:
Craig Matkin, Research Biologist
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. The shortcut to our ASJ news home page is www.asjnews.org.
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Enter keywords such as orca, killer whale, or Steller sea lion to find more information about these interesting animals.
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