As the ice begins to melt in April, the walruses begin moving north, passing through the Bering Strait to the Chukchi Sea by summer. The Chukchi sea ice also is melting more in summer, and scientists have noticed "some very dramatic responses" there, said Chad Jay, a scientist with the U.S. Geological Survey's Alaska Science Center in Anchorage.
With no ice left in their traditional shallow-water feeding grounds, many walruses have migrated to land along the coast.
"But we might be seeing some more subtle changes in the Bering as well," Jay said.
There, the husband-wife team of Cooper and Jacqueline Grebmeier, also a research professor at Maryland's Chesapeake lab, think the melting ice might be affecting more than the walruses' loafing habits. Sampling conducted over the past 25 years by Grebmeier and others has shown declines in the population of bottom-dwelling creatures in the eastern Bering Sea, meaning a decrease in the food supply for walruses, Cooper said.
The researchers think the drop-off in clams and worms could also stem from the changing climate, by affecting the bottom-dwellers' food supply.
Algae, tiny plant-like organisms that are the base of the sea's food chain, grow on the underside of the ice. In spring, lengthening daylight and warming temperatures trigger massive "blooms" of algae in the water along the receding edge of the melting pack. The mollusks and crustaceans on the bottom feed on the fallout from that burst of life in the water.
"Because the ice is starting to disappear earlier," Cooper said, "there may not be as much food getting to the bottom anymore in such a big pulse."
The Maryland research team spent hours outside on the stern of the 420-foot icebreaker, dredging the bottom and then screening out the clams and other creatures in the muck so they could be identified and counted.
Meanwhile, other scientists disembarked from the ship to take ice cores for analysis. As they worked, armed Coast Guard crew members kept watch across the white plain for polar bears that might see the scientists as their next meal.
Jay and his team took off from the Healy in a helicopter to find walruses and tagged 17 of them - from a distance, given the animals' size. Using a crossbow, they fired transmitters with barbed heads into the animals' blubbery hides so scientists could track their movements by satellite.
