Thus far this year, there hasn't been a decline in gray whales but this is the scrawniest they have been since malnourishment and disease claimed a third of their population in 1999 and 2000, the Los Angeles Times reported.

Scientists suspect the same thing may be happening now that triggered the die-off then: rapid warming of Arctic waters where the whales feed.

Whales depend on fat-rich crustaceans to gain enough weight for their long southerly migration. As Arctic ice recedes, there are fewer crustaceans on the floor of the Bering Sea.

In the hunt for food, some gray whales are extending their 5,000-mile northerly migration beyond the Bering Strait into the Chukchi and Beaufort seas north of Alaska, said Steven Swartz of the National Marine Fisheries Service.

"They need to find new places to feed, because the ocean is changing on them," Swartz said. "I hope we are watching a transition rather than a serious problem."