Bowheads Feeding Less in Beaufort Sea
STORY: About the only thing a bowhead whale has to do to get a meal is open its gigantic mouth and swim through the water. Inside the whale's mouth are rows of fibrous plates, called baleen. Baleen acts as a kind of filter to siphon off millions of energy-rich zooplankton. On a good day, a bowhead whale will gorge on more than a ton of these tiny, crustacean-like animals.
And while baleen helps the bowhead gather food, it's also helping scientist Sang Lee learn where bowhead whales feed as they migrate through Arctic waters.
LEE: "Baleen plates provide a continuous record of food sources as it grows. It's a kind of a history of feeding during its life that I can look at."
Lee is a master's degree student at the University of Alaska Fairbanks. He's analyzed the isotopic ratiosa kind of elemental fingerprint of the whale's dietfound in the whale's baleen. He noticed that the level of the isotope, Carbon 13, from prey consumed in the western Arctic's Chukchi Sea was different from the level found in the Eastern Beaufort Sea. By studying these differences, he was able to pinpoint where prey was consumed during the whale's annual migration.
Lee discovered that the Eastern Beaufort Sea above Alaska and Canada is an important feeding area for bowhead whales, especially subadult whales. He also discovered that the younger bowhead whales feed about ten percent less in the Eastern Beaufort Sea today than they did during the mid-1980s.
LEE: "They were believed to feed intensively in the Eastern Beaufort Sea, but actually my stable isotope data show that the Eastern Beaufort Sea is not the main feeding ground. In contrast, the Bering/Chukchi seas provide the most food for the bowhead whales. I'm not saying they don't feed at all in the Eastern Beaufort Sea. The Eastern Beaufort Sea gives them a second feeding ground. It's not the first one."
Overall, Lee learned that subadults derived about 16 percent of their annual nutrition from the Eastern Beaufort Sea, while adults obtained only about 5 percent of their yearly food intake from the region. The findings have stirred interest among other whale scientists, including John Craighead George, a whale biologist with the North Slope Borough in Barrow, Alaska.
GEORGE: "When the bowheads migrate up along the Alaska coast into the Canadian Arctic, certainly they're headed there with the expectation of finding food. So there's no question that behavioral observations show them feeding. The question is the proportion. I don't think that case is closed."
Lee says that while the whales may migrate to the Eastern Beaufort Sea to feed, changing ocean conditions may be making it harder for them to find food. Lee suggests that Arctic codfish may be increasing in number and competing with bowheads for prey. And he doesn't rule out the possibility that climate warming also may play a role.
Lee's study is important to wildlife officials as well as to Native whalers and even oil developers interested in tapping vast petroleum reserves believed to lie beneath the Arctic Ocean. George worries that oil interests might interpret the research as meaning the Eastern Beaufort Sea is no longer as important to bowhead whales.
GEORGE: "The obvious implication, if they are only deriving a small portion of their annual food, might be for the leasing agency like the federal Minerals Management Service to say that it's not terribly important and therefore we can develop these areas. They have not made that decision, but that would be a logical outcome I would think."
George says that Lee's study of 33 whales, taken during a three-year period in the mid-1980s and during another three-year period in the late 1990s, is not a long enough time-series to reach any final conclusions. He says additional research now under way to measure plankton biomass and monitor bowhead feeding behavior will shed more light on just where Alaska's bowhead whales go and what they eat.
OUTRO: This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program and the University of Alaska Fairbanks. I'm Doug Schneider.
Thanks to the following individuals for help preparing this script:
Sang Heon Lee, M.S.
John Craighead George, Wildlife 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.
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Within each year, bowhead whales share a common song type, but the song changes from year to year. Bowhead whale vocalizations are provided courtesy Cornell University Laboratory of Ornithology and the North Slope Borough, Department of Wildlife, Barrow, Alaska. Used with permission. Requires RealAudio.
Related links:Book: Guide to Marine Mammals of Alaska