ShareThisSAN FRANCISCO - The massive gray whales that migrate each year between Alaska's Bering Sea and Baja California have survived thousands of years of sea-level and climate change by altering the way they live and feed, scientists at the University of California, Berkeley have found.
Those major adaptations could put the creatures in good position to withstand climate change taking place today, they said.
Long before now -- perhaps 2 million years ago or more -- evolution shaped gray whales' skulls, allowing them to find food in two very different ways.
Today, they can dive to the ocean bottom and suck up the muddy sediments that their whisker-like baleen will filter out to get tons of nutritious worms and tiny crustaceans -- as much as 900 pounds a day. Or they can swim through the open water with mouths agape to filter out masses of krill, herring and other small fish.
One small group of gray whales along the North Pacific coast no longer migrates to the Bering Sea from Baja each year nor forages for food in the ocean sediments off Alaska.
Instead, those whales remain year round near Vancouver Island in Canada and off the tiny Humboldt County, Calif., town of Trinidad, a one-time whaling center. They use what the scientists call a "diverse set of feeding modes" that has turned them into hunters of the open ocean -- like their relatives, the blue whales and the humpbacks.
The behavioral change has occurred since the last ice age ended some 10,000 years ago and sea levels rose. That evolution of their skulls made it possible.
David Lindberg, an evolutionary biologist at Berkeley, and Nicholas Pyenson, a former Berkeley graduate student and now curator of fossil marine mammals at the Smithsonian Institution in Washington, used the many cycles of past climate and sea level changes to study the whales' survival patterns.
Their study is published in the current issue of the online journal PLoS One.
The scientists focused on the changes in sea levels that occurred between 120,000 years and 10,000 years ago, when glaciers and ice sheets alternately advanced far south from the Arctic and retreated again and again.
The oceans also froze and sea levels shrank, then warmed again, and sea levels rose. With those changes came alterations in food availability. Some whales, including the grays, met those challenges by diversifying their way of life, the scientists have found.
Lindberg and Pyenson estimate that long before humans arrived on the West Coast, gray whales throughout the North Pacific Ocean could have numbered as high as 120,000. But commercial whaling, beginning about 1845 and continuing into the early 20th century, killed off thousands of whales of virtually every species.
Rigorous protection since then has restored gray whale numbers to about 22,000, Lindberg and Pyenson estimate. As climate change continues and the North Pacific's water warms, the gray whales' "plasticity" -- their ability to find food in diverse ways -- should give them a distinct advantage, they say.
"I suspect the gray whales will be among the winners in the great climate change experiment," Pyenson said.
(Email reporter David Perlman at dperlman(at)sfchronicle.com.)
(Distributed by Scripps Howard News Service, www.scrippsnews.com.)
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