Heat sensors offer scientists new way to count walrus

Posted: Tuesday, June 24, 2003

ANCHORAGE - The hot bodies of Pacific walruses snoozing on sea ice may offer federal scientists the first reliable way to count the marine mammals throughout their vast Bering Sea range.

For the second spring in a row, U.S. Fish and Wildlife Service biologists and technicians have tested a heat-sensing scanner mounted in the belly of an airplane to find walrus groups scattered amid broken ice floes.

Preliminary results look promising, investigators told the Anchorage Daily News. The method could lead to an international walrus count as soon as 2005, producing the first population estimate in more than a decade.

The one- to two-ton marine mammals roam shallow waters of the Bering and Chukchi seas, often near the ice edge, eating clams and other invertebrates from the sea floor. They serve as an important source of food, ivory and skins for the 18 villages of the Eskimo Walrus Commission.

Walruses are notoriously hard to count because they spread out in small groups over thousands of square miles. Depending on the season, they could be found from Bristol Bay to the Chukotka Peninsula on both sides of the Russia-U.S. border.

Scientists stopped trying to count them in 1990 because no method worked. But gauging the health of the species will become essential if global warming continues to shrink sea ice and change where the animals look for food, said lead investigator Doug Burn, a U.S. Fish and Wildlife Service biologist in Anchorage.

Over six days in early April, a team spent about 40 hours flying survey tracks almost two miles above the sea near St. Lawrence and Nunivak islands. They were looking for the thermal signature of the fat brown mammals.

As the plane hurtled along at 230 mph, the infrared scanner would record the total warmth generated in 1,500 living-room-size squares spread in a strip across 3.7 miles of ocean. Burn likened the high-altitude, high-tech scan to "mowing the lawn."

"The autopilot will keep us on down the line at a constant speed," he said. "Actually it's pretty boring up there."

What the thermal surveying lost in thrills, it gained in accuracy and volume. Groups of 10 walruses or more would show up immediately, with exact locations and heat recorded on the computer. Every hour the scientists would cover about 850 square miles, four times the area they could have scrutinized by watching for walrus through airplane windows.

At least once a day, the team flew lower and took digital photographs to get an exact count of animals in certain sample groups. By comparing the number of walruses in the pictures with the amount of heat they generated, scientists hope to produce a sort of walrus heat index that could be applied to the entire area.

The walrus study was originally funded in 2002 with a $208,000 grant from NASA, along with other remote-sensing projects.

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