Warming May Be Hurting Gray Whales' Recovery
Tuesday, September 11, 2007
As many as 118,000 gray whales roamed the Pacific before humans decimated the population through hunting, and human-induced climate change may now be depriving those that remain of the food they need, according to a study released yesterday.
The research, based on a detailed analysis of DNA taken from gray whales living in the eastern Pacific, highlights how human behavior has transformed the oceans, the scientists said.
Today there are only about 22,000 Pacific gray whales, including about 100 in the western Pacific. By examining the genetic variability of the current population, scientists at Stanford University and the University of Washington at Seattle calculated that there were between 76,000 and 118,000 gray whales in the Pacific before commercial whaling in the 1800s shrank their numbers.
Federal officials took eastern Pacific gray whales off the endangered species list in the mid-1990s, but a rise in sea temperatures appears to have limited the whales' available food. A recent spike in deaths among gray whales may suggest "this decline was due to shifting climatic conditions on Arctic feeding grounds," the researchers wrote in the paper, being published online this week in the Proceedings of the National Academy of Sciences.
"There definitely are large-scale ecosystem effects going on," said Stanford doctoral student S. Elizabeth Alter, the lead author, in an interview yesterday.
"One of the most exciting things" about DNA analysis, she said, is that it gives us "the opportunity to look back in time and see what the ocean looked like before human impact."
The decline in gray whales has affected the ocean in a variety of ways, according to the researchers. Because the animals feed on the ocean bottom by sucking in and expelling sediment that contains shrimplike creatures called amphipods, the scientists wrote, historic populations may have redistributed enough sediment to feed a million seabirds.
Aboriginal tribes are currently allowed to kill as many as 125 eastern Pacific gray whales a year under International Whaling Commission rules, though this practice has sparked controversy. In light of the new data suggesting that the whales' numbers were more depleted than was previously known, international officials need to reconsider the amount of gray whale hunting they currently allow, the researchers said.
On Saturday, five members of Washington's Makah tribe shot and killed a gray whale without the required permit. Coast Guard officials caught the men and turned them over to tribal police. On Sunday, tribal council leaders issued a statement denouncing the men's actions and vowed to prosecute them.
Stephen R. Palumbi, a professor of marine sciences at Stanford and a co-author of the study, said the research suggests that given the right conditions, the number of gray whales could increase in the years to come. But a warmer Bering Sea could impede this recovery, he said, because it is killing off some of the food the whales consume.
When emaciated gray whales washed ashore between 1999 and 2001, scientists initially speculated that the animals were exhausting the ocean's "carrying capacity," Palumbi added, but it could be instead that global warming is to blame.
"It's not a conclusion we can come to. It's a hint," he said in an interview. But if humans are affecting the ocean's "capacity to support life, it's got to make you worry, it's got to make your wonder."