A giant of the sea finds slimmer pickings
Gray whales are skinnier, and scientists suspect Arctic warming is the reason why
"That female looks a little skinny," said federal biologist Wayne Perryman, peering through his binoculars. "You can see her scapula sticking out. Yeah, she's a skinny girl."
So far this year, scientists haven't seen a decline in numbers, and they are not sure what's causing the whales to be so thin. But they suspect it may be the same thing that triggered the die-off eight years ago: rapid warming of Arctic waters where the whales feed. Whales depend on cocktail-shrimp-size crustaceans to bulk up for their long southerly migration. As Arctic ice recedes, fat-rich crustaceans that flourished on the
Skinny whales were first spotted this year in the protected waters of San Ignacio Lagoon in
That's where a team led by Steven Swartz of the National Marine Fisheries Service in Silver Spring, Md., and Jorge Urban of the Autonomous University of Baja California Sur noticed that about 10% looked more bony than blubbery, a telltale sign of malnutrition.
Instead of making steady progress during their long migrations, the whales have been stopping often to eat along the way.
They have been seen straining mysid shrimp from kelp beds off
Such opportunistic feeding has its risks. Switching to new food can expose the whales to harmful parasites as well as other hazards. There have been at least two fatal accidents this spring near
To find food, some gray whales have been expending more energy by extending their 5,000-mile northerly migration beyond the Bering Strait into the Chukchi and Beaufort seas north of
It used to be a rare occurrence to see gray whales off Barrow,
Their arrival has become an annoyance and even a navigational hazard for local Inupiat (Eskimo) subsistence hunters, who have permits to hunt bowhead whales but not grays. "A few people have been running skiffs along the coast and have hit them," George said. "During fall bowhead whale hunting season, they see a blow and divert off course only to find it's a gray whale."
Historically, the eastern Pacific gray whales congregated every summer in the shallows of the
"You could practically walk across the gray whales in the
The carpets of crustaceans were frayed and, in some places, gone.
Scientists first thought that the gray whale population, which had been hunted nearly to extinction in the 1930s, had simply grown too large for its primary food source and eaten more than nature could provide. Such overgrazing was thought to have been responsible for the mass die-off in 1999 and 2000 that saw the population drop from 26,600 to about 17,400.
Now scientists suspect that the climatic changes in the
These amphipods grow in tubes on sandy or muddy seafloors and cannot move around like many sea creatures. They count on bits of algae to come to them, or at least close enough so they can use their antennae to pull the food into their mouths.
One source is a confetti that rains down from shaggy mats of algae that grow on the underside of ice sheets at the ocean's surface. Another is brought by ocean currents, carrying a soupy mix of algae or plankton.
Both sources have diminished or been cut off as the northern
Whales are not the only animals struggling to adapt to these rapid changes. Researchers have also noticed dramatic declines in other species that feed on the bottom, such as walruses and sea ducks.
Federal scientists believe the gray whale population is holding steady at 18,000, although they are working on an updated estimate.
The population had been growing steadily until 1998, the year of a warm El Niño now seen as a turning point for the
"The gray whales don't seem as robust as they once were," said Perryman, a National Marine Fisheries Service scientist in charge of the annual count of gray whale cows and calves.
He and his crew keep watch 12 hours a day from March to June tallying each gray whale that passes by the Piedras Blancas Lighthouse near San Simeon's
The loss of
"These animals are feeding on things that scientists haven't observed in modern times," said Bruce Mate, director of the Marine Mammal Institute at
But switching food could expose them to parasites that contribute to their emaciated condition, scientists say.
It's possible, Swartz and other researchers said, that their scrawniness is merely a temporary condition as the whales learn to adapt to a rapidly changing
"Gray whales are good at switching prey," Swartz said. "They need to find new places to feed, because the ocean is changing on them. I hope we are watching a transition rather than a serious problem."