Gray whales losing weight

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 one-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 might 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 percent 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 off Santa Barbara 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 sea-floor 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.

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 sea-floor 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. “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.

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 and vanishing sea ice.