Plunge of gray whale numbers may be from drop in food supply

Tuesday, July 2, 2002

They kept washing ashore, hundreds of them. The huge but emaciated bodies of gray whales floated lifeless into Puget Sound and San Francisco Bay, and drifted onto beaches from Alaska to Baja California.

The putrid carcasses became such a nuisance in 1999 and 2000 that beach communities took to towing the 35-ton cadavers out to sea or burying them with backhoes. Eskimo whalers reported harpooning "stinky" whales that appeared to be rotting alive, too smelly even for dogs to eat.

Although the die-off has stopped, as mysteriously as it began, the most recent tally shows the gray whale population has plunged by more than one-third, falling from an estimated peak of 26,635 whales in 1998 to 17,414 this spring -- the lowest in nearly two decades.

"That's a jolting decline for a long-lived species," said Ray Highsmith, a professor of marine science at the University of Alaska, Fairbanks, and an expert on the main food source for gray whales. "If the numbers are right, there's something seriously wrong."

The die-off was a stunning setback, coming as it did just five years after the whales had been taken off the endangered species list. The grays, all but extinct in the 1930s, had appeared to be thriving by the mid-1990s.

Can't blame hunting

Particularly troubling has been the inability of scientists to pinpoint the cause. Hunting, the old nemesis, could not be blamed. Only 140 gray whales are taken each year by Eskimo and Native American hunters, the only people allowed to kill them.

Exactly what has gone wrong remains a topic of considerable debate. One scientist thought it was the flu. Another blamed chemical pollutants. Others pointed to the cyanide-based fluorescent dye used to mark illegal narcotics drops in the ocean. Was it collisions with boats? Navy sonar experiments exploding whale eardrums? Killer whales with outsized appetites?

"All of a sudden, in 1999, the bottom fell out. We went from 1,400 calves to 420. Strandings jumped from 35 to 270," said Wayne Perryman, a biologist with the Southwest Fisheries Science Center in San Diego. "That's not a subtle signal."

The casualties didn't just include the sick, weak, young and very old. Many of the dead mammals should have been in the prime of their 50-year lifespan.

In the spring of 2000, veterinarian Frances Gulland of Sausalito's Marine Mammal Center in California conducted full necropsies on three animals and found as many distinct causes of death: viral encephalitis, the biotoxin domoic acid, and parasitic abscesses. "All of those could have initially started as malnutrition," Gulland said. "The real question is, why were they so malnourished? Why did they get whatever caused them to die?"

A team of Alaskan biologists is now conducting the first in-depth chemical analysis of fresh samples of gray whale blubber in the hunt for clues.

All were scrawny

There has been one common denominator in both the living and dead: Many of the animals were so skinny that their ribs stuck out. The scrawniness was visible from aerial photographs.

Bruce Mate, an expert at Oregon State University and Sea Grant on endangered whales, thinks there isn't enough food because there are too many whales. "Our leading hypothesis is, they actually overshot their food supply," he said.

Mate's "starvation hypothesis" presumes a dark side to the whale's spectacular recovery -- that the population can rise only so high before being cruelly adjusted back into equilibrium with nature.

"The two years we saw of die-offs and strandings was the adjustment," he said.

Respond to this story

Posting a comment requires free registration: