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Thousands of walruses have gathered on an island near the coast of Alaska in their earliest ever appearance because of exceptionally warm ocean temperatures.

The Pacific walruses were spotted on the barrier island off the coast of Point Lay, about 700 northwest of Anchorage, U.S. Fish and Wildlife Service spokeswoman Andrea Medeiros said.

Sea ice along northern Alaska disappeared far earlier than normal this spring as a result of exceptionally warm ocean temperatures.

The receeding ice has forced the animals to seek land earlier, allowing immature walruses to rest as their mothers dive over the shallow continental shelf to eat clams and snails.

Ms Medeiros said: "This is the earliest date that large numbers of walruses have been confirmed on shore at Point Lay," adding that it was the first time a herd has been seen as early as July.

Since 1981, an area more than double the size of Texas - 610,000 square miles - has become unavailable to Arctic marine mammals by summer's end, according to the National Snow and Ice Data Center.

The U.S. Fish and Wildlife Service has notified the Federal Aviation Administration, the U.S. Coast Guard, and barge companies and airlines serving Point Lay that walruses are in the area, Ms Medeiros said.

he federal Marine Mammal Protection Act prohibits the "take" of walrus, which includes disturbance from human activity.

Sea ice usually melts to its summer minimum sometime in September.