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Scientists try heat to find reliable way to count walrus

Posted: Monday, May 13, 2002

ANCHORAGE (AP) -- The heat contrast between the icy Bering Sea and Pacific walrus may help scientists count and protect the population of the one or two-ton animals.

Using an infrared, heat-sensing scanner mounted in the belly of an airplane, researchers from the U.S. Fish and Wildlife Service spent two weeks in April flying over walrus groups hauled out on ice floes near St. Lawrence Island so they could record digital images of their temperatures. The island is about 620 miles northwest of Anchorage

The team battled bad weather but flew about 52 hours over the ice-covered Bering Sea, taking detailed images of about 20 walrus groups. By matching thermal information with aerial photographs of the same groups, the scientists hope to calculate a reliable method for gauging walrus numbers by body heat alone.

''It's like mowing the lawn,'' said federal biologist Douglas Burn. ''You basically go back and forth, and you let thermal sensor sample the sea ice, and you let it find the walruses for you.''

This walrus study is just one example of how scientists have been studying land and sea from remote sensors in satellites and aircraft. Biologists have searched out polar bear dens in Alaska with a different kind of infrared device. Other researchers have been using imagery to profile geographic features of entire regions.

Counting walruses has always been difficult. They gather in small groups as they forage for clams and other invertebrates across a remote sea. Depending on the season, the animals could be distributed over thousands of square miles from Bristol Bay to the Chukchi Sea, on both sides of the Russia-U.S. border.

''For over 12 years now, there has not been a population census,'' said Austin Ahmasuk, director of the Eskimo Walrus Commission in Nome. ''Many scientists are theorizing and projecting certain trends, but it's purely conjecture.''

''The first question is how many are there,'' Burn said. ''But walrus life history, the way they are, makes it very difficult to figure that out.''

Knowing the population has never been more critical. Walruses are hunted in almost 40 Alaska and eight Russian communities, and they serve as a major source of food, ivory and skins in the 18 villages represented by the commission, Ahmasuk said. Between 6,000 and 8,000 animals were harvested or struck in 2000, according to Ahmasuk and the federal stock assessment.

While some hunters report that some walruses have been spreading into new habitat, with young females producing calves, others have killed walruses with thin layers of blubber, Ahmasuk said.

''I have a mixed feelings from hunters regarding trends,'' Ahmasuk said, though ''overall they seem to get the impression that the population is doing fine.''

Between 1975 and 1985, U.S. and Russian biologists conducted surveys every five years, often using different methods or working at different times. Population estimates ranged from about 200,000 to nearly 240,000 animals but were never precise enough for scientists to estimate trends.

A joint operation conducted in 1990 did not produce reliable numbers either, partly because warm weather drove the ice edge farther north than normal, changing the distributions. After that, scientists agreed to suspend surveys until they could figure out a more reliable method, according to the federal walrus stock assessment report published in February.

The very aspects of walrus biology that make them so hard to count by eye might make them easy to pinpoint through remote sensing from aircraft flying faster and higher, Burn said. Walruses, especially large groups piled up together on ice floes, produce heat, Burn said.

''That's the idea, to let the (infrared device) do the sensing for you,'' Burn said. ''In order for us to develop the technique, we need lots of data.''

The walrus study is among eight projects funded last year by a $3.5 million NASA grant, secured by Alaska Sen. Ted Stevens, to test remote sensing technology in Alaska. The other studies include mapping land formations to help find gold deposits, locating stands of beetle-killed spruce trees and a $1.2 million effort to track high-seas drift nets.



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