SAN SIMEON, CALIF. — A female gray whale labored up the coast, the bony ridge of a shoulder blade protruding from what should be the smooth, plump roundness of healthy blubber.
"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."
Scientists from Mexico to the Pacific Northwest are reporting an unusually high number of scrawny whales this year for the first time since malnourishment and disease claimed a third of the gray whale population in 1999 and 2000.
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 Bering Sea floor are becoming scarce.
Skinny whales were first spotted this year in the protected waters of San Ignacio Lagoon in Baja California, where gray whales spend the winter breeding and nursing their calves before returning every summer to the Arctic.
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 California and British Columbia, sucking up mouthfuls of sand in Santa Barbara Harbor and skimming surface waters for krill-like crustaceans all along the West Coast.
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 San Francisco's Golden Gate Bridge. Gray whales, surfacing to breathe after dining on seafloor snacks, have been ripped apart by propellers on cargo vessels.
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 Alaska.
It used to be a rare occurrence to see gray whales off Barrow, Alaska, said Craig George, a North Slope Borough wildlife biologist since the 1970s. In recent years they have become summertime regulars, churning up mud plumes along the shoreline in search of food.
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 Chirikov Basin, a place in the north Bering Sea known for its vast seafloor carpets of crustaceans called amphipods. The whales sucked in great mouthfuls, straining out the sand and mud, packing on the pounds in the few months before their long annual journey to Baja and back.
"You could practically walk across the gray whales in the Chirikov Basin in the 1980s," said Sue Moore, a former director of the National Marine Mammal Laboratory in Seattle who has conducted aerial surveys. "They were stacked up to the horizon. In 2002, I went back and everything had changed."
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 Bering Sea played a role in the population plunge by reducing the whale's primary food: amphipods that appear to be affected by warming temperatures and vanishing sea ice.
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.