ANCHORAGE - Alaskan researchers are joining their Russian counterparts in the most exhaustive effort yet to answer a simple question: How many walrus are there?
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Without a good answer, it is impossible to know if the marine mammals that live mostly on sea ice off the coasts of Alaska and Russia are being affected by global warming, according to scientists on both sides of the Bering Strait.
"The size of the walrus population is unknown. We really have no idea," said Douglas Burn, a wildlife biologist with the U.S. Department of Fish and Wildlife in Anchorage.
Without some basic knowledge, it is impossible for scientists to advise policy makers on whether walrus should join polar bears, now being recommended for listing as threatened under the Endangered Species Act. The proposed listing is based largely on the belief that sea ice is melting.
Walrus, too, are very dependent on sea ice. They give birth on the ice and rest on it. The hefty animals need ice that is a minimum two feet thick to support their weight.
A joint aerial survey to count walruses was conducted every five years between 1975 and 1990, when scientists estimated there were about 200,000 Pacific walrus. Researchers lost enthusiasm for the survey after realizing it was not providing an accurate count.
Now, researchers in Alaska and Russia are bringing modern sampling methods to the count. Those methods include a special walrus tag attached with a crossbow, infrared scanning, a digital camera and satellite telemetry.
The survey area covered more than 38,610 square miles.
"It has to be done jointly otherwise it doesn't reflect the truth," said Vladimir Chernook, department head of the Research and Engineering Institute for the Development and Operation of Fisheries in St. Petersburg, Russia. "The walrus don't care about the border."
The survey is being funded with about $1.5 million in U.S. money.
The improved walrus count began with scientists at the U.S. Geological Survey developing a special transmitter that can tell when walruses are on the ice and in the water. Previous walrus counts missed the walrus in the water. A crude correction factor was applied but the end result was likely an undercount, said Chad Jay, a research ecologist with the U.S. Geological Survey in Anchorage who helped develop the new tags.
The tags take into account wind speed, temperature, barometric readings and animal behavior in estimating how many walrus are likely in the water at any given time.
In March 2006, scientists hoped to attach about 90 tags but ended up attaching about half that amount because of bad weather and permitting problems in Russia. Most of the tagging was done over 10 days south of St. Lawrence Island, about midway between Russia and the United States.
Scientists used a crossbow to attach the transmitters to the walruses between their shoulder blades. After about six weeks, the transmitter battery dies and the barb anchoring the device eventually works its way out of the animals' thick layer of blubber, Jay said.
The following month, over 50 scientists, three airplanes and two ice breakers were recruited for the joint survey. It was conducted over three weeks when the walrus are spread over the ice fields of the Bering Sea.
"When you plot the data, you can see it is all part of the same concentration of walrus. They go where the ice goes," said Burn, leader of the aerial survey crew who developed the thermal imaging system.
When the scientists detected a group of walrus, the infrared scanning was used to detect how much heat the walrus were producing. It is the intensity of the heat that is used to determine how many walrus were in each group.
Photographs were compared to thermal images to come up with a formula. The formula can be applied to thermal images taken over a large expanse, Jay said.
The summer will be spent refining the data. A preliminary count is expected by this fall.