California gray whales such as the three trapped by Arctic ice off Alaska's northern coast have one of the longest migration routes of all mammals and are among the last of their species.

The trapped whales didn't leave in time on the annual migration from the Arctic Ocean to the warm water off Baja California, a journey of 6,000 to 8,000 miles.California gray whales must leave the Arctic before winter because they are not adapted for icy conditions and have relatively thin blubber for insulation, said Mark Palmer, executive director of the Whale Center in Oakland.

He said the whales also cannot break through ice and cannot dive underneath ice for any great distance.

The whales can spend an average of only three to six minutes underwater at a time during their migration, he said.