ANCHORAGE, Alaska (Reuters) – U.S. government biologists have launched a special investigation into the deaths of at least 70 gray whales washed ashore in recent months along the U.S. West Coast, from California to Alaska, many of them emaciated, officials said on Friday.

The National Oceanic and Atmospheric Administration (NOAA) declared the whale die-off an “unusual mortality event,” a designation that triggers greater scrutiny and allocation of more resources to determine the cause.

So far this year, 37 dead gray whales have turned up in California waters, three in Oregon, 25 in Washington state and five in Alaska, say officials of NOAA’s National Marine Fisheries Service. Five more were found in British Columbia.

The most recent dead whale in Alaska was spotted last week near Chignik Bay on the Alaska peninsula.

Many have little body fat, leading experts to suspect the die-off is caused by declining food sources in the dramatically warming waters of the northern Bering Sea and Chukchi Sea off Alaska.

The gray whales summer there, consuming most of a year’s worth of nourishment to pack on the blubber they need to carry them through the migration south to wintering grounds off Mexico and back north to feeding grounds off Alaska.

Sea ice has been at or near record lows in the Bering and Chukchi, and water temperatures have been persistently much higher than normal, an apparent consequence of human-caused climate change, scientists say.

The conditions the whales encountered last summer could be hurting the animals now as they make their annual migration north, said scientists assembled by NOAA for a teleconference on Friday.

“The Arctic is changing very, very quickly, and the whales are going to have to adjust to that,” Sue Moore, a University of Washington oceanographer, told reporters.

Lack of sea ice may be reducing supplies of the tiny crustaceans known as amphipods that are the gray whales’ prime food source, Moore said.