A whale of a problem

The long-heralded success story of the Pacific grey whales' recovery from near-extinction might be wrong, according to a genetic analysis that pegs the present population at only one third to one fifth of their historical levels.

By examining subtle variations among DNA taken from 42 modern whales, scientists have concluded that between 78,500 and 117,700 grey whales lived before the heyday of commercial whaling in the Pacific in the 19th and 20th centuries.

That finding, published recently in the Proceedings of the National Academy of Sciences, suggests that the roughly 22,000 grey whales now swimming along the California coast remain a depleted population in transition.

"It's startling for us to consider the California grey whale, which we considered recovered, has not recovered after all," said Scott Baker, a researcher at Oregon State University's Marine Mammal Institute.

The results counter what had been a predominant scientific view that the iconic creatures of the West Coast had become so bountiful that they were damaging their traditional feeding grounds by overgrazing.

Instead, the new findings provide evidence that this year's abnormally high number of skinny whales is a sign of deterioration in the food chain of the ocean ecosystem stretching from Baja California to the Bering Sea.

"If the oceans a few hundred years ago could support 100,000 grey whales, why can't the oceans sustain 20,000 whales today?" said Stephen Palumbi, a Stanford University marine sciences professor and senior author of the study.

Shocking estimate

Palumbi threw the scientific community into disarray four years ago when he and a Harvard University colleague estimated that the humpback, fin and minke whales in the North Atlantic were once two to ten times more abundant than their present population levels.

Besides challenging conventional estimates, their study presented a political problem for the International Whaling Commission (IWC), which oversees a global ban on commercial hunting.

The commission has long promised to allow whaling nations such as Japan and Norway to resume operations once certain species have recovered to 54 per cent of historic levels. In the case of humpback whales, Palumbi estimated it would take another 70 to 100 years before the population reached such a threshold.

Grey whales are now hunted by native peoples, who are allowed to kill up to 140 animals each year. Nearly all are harpooned by traditional Russian hunters off the coast of Siberia, although Washington State's Makah Tribe has been trying to reassert its right to hunt grey whales.

The DNA-based estimates of historical populations are unlikely to change those limits, which most experts agree are not high enough to affect the stability of the whale population.

But the new DNA-based estimates undermine the scientific foundation of the whaling commission's estimates of the health of whale populations in general.

"It's going to prompt both the IWC and the National Marine Fisheries to reconsider," Baker said. "Whether it will convince them to change management, I'm not sure."

Scientists previously have relied on whalers' log books and records of sales of barrels of oil — and more recently, computer models — to estimate past populations of the behemoths. The methods were crude, producing estimates ranging from 15,000 to 20,000, though some models generated figures several times as high.

To construct a more precise estimate, Palumbi relied on the genetic principle that mutations accumulate slowly over time. He and his colleagues, graduate students Liz Alter of Stanford and Eric Rynes of the University of Washington, examined DNA samples from 42 grey whales that had been washed ashore or were biopsied at sea. They looked in ten specific places that they believed have mutated independently.

Since mutations accumulate slowly, the degree of difference between the whales works as a kind of yardstick, indicating how many generations have passed since they shared a common ancestor.

The researchers used computers to calculate the number of ancient breeding whales that would have been necessary to produce the genetic patterns obtained in their samples. Factoring in that some adults don't breed, the proportion of juveniles and other factors, they concluded that at least 78,500 and no more than 117,700 grey whales must have roamed the Pacific.

Uncertain reasons

Palumbi said that population was at least 1,600 years ago. He said there was no way to tell if the population was stable until the onset of commercial whaling or if it already had been declining from aboriginal hunting or unknown natural causes.

Rob Fleischer, who heads the Centre for Conservation and Evolutionary Genetics at the National Zoo in Washington DC, said the study was convincing because of its detailed genetic analysis. The population estimates are "still a lot more than anybody thought, even at the bottom end of the distribution", he said.

The new study, funded by the National Institutes of Health, Stanford and several private foundations, has not generated the scientific scepticism of Palumbi's first effort to use genetics to estimate the populations of humpback, fin and minke whales.

Phillip Clapham, a leading whale researcher in the National Marine Mammal Laboratory in Seattle and vocal critic of the first population genetic study, said the low end of the new estimated range nearly overlaps with a few of the traditional estimates. Regardless of the historic number of grey whales, the oceans have changed since the days when "humans started killing them and mucking with their ecosystem", he said.

The grey whale population plummeted to 17,400 after starving whales began washing ashore in 1999 and 2000. Scientists believe that the rapid warming of the Arctic waters has frayed a seafloor carpet of crustaceans in the Bering Sea that has long been a grey whale food staple.