Global Warming May Be Keeping Gray Whale Numbers Down

Stefan Lovgren
for National Geographic News
September 10, 2007

Eastern gray whales were once three to five times more numerous in the Pacific Ocean than today, and climate change may be the cause of the population decline, a new study says.

According to a recent census, about 22,000 eastern gray whales currently live in the Pacific.

Experts had thought this to be around the whales' natural population level, because of widespread die-offs of gray whales between 1999 and 2001 that plunged the animals to 18,000 individuals.

But scientists studying whale DNA have concluded that the Pacific whale population previously ranged from 76,000 to 118,000.

(Related: "Climate Change Harming Bering Sea Mammals, Birds, Study Shows" [March 9, 2006].)

"Our results suggest that rather than looking at this historical carrying capacity as the cause behind these die-offs, we might be better off looking at the changing conditions on the gray whale feeding ground that we know are occurring," said Elizabeth Alter, a doctoral biology student at Stanford University in Palo Alto, California.

Alter is the lead author on the study, which appears this week in the journal Proceedings of the National Academies of Science.

DNA Discovery

Gray whales, which can reach a length of more than 50 feet (16 meters) and a weight of 36 tons, were extensively hunted in the 19th century.

The western, or Asian population remains one of the world's most endangered whale populations. Only 120 western individuals now remain, primarily because of continued whaling.

The eastern gray whale population, however, is one of the few that is believed to have fully recovered to its pre-whaling numbers. In 1994 the whales were even removed from the U.S. list of endangered and threatened species.

But the new study suggests that the eastern population may in fact still be depleted from its historical levels.

Continued on Next Page >>




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