The carcasses were found on the coast of the Chukotka Peninsula near the Chegitun River on August 8. Officials had said they believed that the walruses were slaughtered by poachers for their valuable tusks in late July.
However, experts with the WWF's Polar Bear Patrol project said: "It is extremely difficult to hunt so many walruses on ice and it would be strange to bring the bodies to the shore."
"It is clear that border guards found remains of walruses that died last autumn," the WWF said on its Web site. "Most probably the animals died during long swimming through rough ice-free sea, from drifting ice to the mainland coast," or due to over-crowding in coastal haulouts, the statement said.
An inspection carried by the Polar Bear Patrol in November and December 2007 revealed that over 1,000 dead walruses were stranded on the arctic coast of Chukotka.
During the summer, walruses form colonies in many parts of Chukotka and at a few remote areas in Alaska. During the winter, they can be also seen in eastern Kamchatka and the Commander Islands.