A giant of the sea finds slimmer pickings
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.
Both sources have diminished or been cut off as the northern Bering Sea has undergone a shift from a seasonally ice-dominated region to more of an open ocean dotted with thin ice that is quickly broken up by storms. And the basin’s waters have warmed enough to allow new types of fish to migrate north, gobbling up the amphipods or competing with them for food.
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 Nino now seen as a turning point for the Bering Sea’s amphipod beds. Since then, the annual tally of calves has fluctuated. This year’s was one of the lowest since the federal government began keeping track in 1994.
“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 Hearst Castle on California’s Central Coast. Perryman believes that the number of calves plunges when whales do not get enough to eat.
The loss of Bering Sea feeding grounds is responsible for another trend: An increasing number of whales don’t bother heading that far north. Some stop at Alaska’s Kodiak Island. Others don’t get even that far and spend summers near British Columbia’s Vancouver Island or off the Oregon coast. Smaller groups remain off California, feeding on shrimp in kelp beds or anything else they can scrounge.
“These animals are feeding on things that scientists haven’t observed in modern times,” said Bruce Mate, director of the Marine Mammal Institute at Oregon State University. “They are beginning to become more diverse in their diet because they have to.”
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 Arctic.
“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.”