Gray Whale watching in Big Sur California, eschrichtius robustus
Gray Whale watching in Big Sur California, eschrichtius robustus
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A Whale of a Food Shortage

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Eschrichtius robustus

Reported in the LA Times, June 24, 2002
A Whale of a Food Shortage
The grays, which used to be growing in numbers, have plunged by a third in four years. Now scientists think they know why.

"Our leading hypothesis is, they actually overshot their food supply."
-- Bruce Mate, whale expert at Oregon State University


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.

Gray Whale with barnacles, photo by Nancy Black, Monterey Bay Whalewatch 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 at 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.

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 the animals.

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?

Current thinking centers on the whale's food supply. The recovering population of whales simply may have been eating more than nature could provide. At the same time, nature itself, buffeted by global warming and shorter-term climate changes such as El Niño, may have been producing less of the cocktail-shrimp-sized sea-floor amphipods that are the primary food of grays.

"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 La Jolla. "That's not a subtle signal."

The casualties didn't just include the sick, weak, young and very old. Many of the dead animals 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 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.

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.

As for the medicine-like stink that prompted complaints from Eskimo hunters, Perryman said it could have been a result of a defective metabolism or simply the stench of starvation. "Just like with human beings, their breath is affected by what they're eating," he said. The breath of gray whales might be rancid, he said, because they are breaking down deep energy reserves and protein, instead of burning calories from recently ingested food or their own blubber.

If the whales were starving, what happened to their food?

Gray Whale Skeleton The 35- to 50-ton whales spend their summer in the Bering Strait, gorging on millions of amphipods—crustaceans that live in tubes in the mud and sand on the shallow ocean floor. The whales dive for the critters, sucking in mouthfuls of ocean bottom. They strain mud and sand out through baleen, and swallow the amphipods.

Although they can eat other things, studies of whale stomach contents show that one species of amphipod—Ampilesca macroephala—makes up 95% of the whale's Arctic diet. Because whales eat little while migrating or basking in Baja, the blubbery animals must do a year's worth of fattening up on this one species in the few months they spend near the Bering Strait.

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.

Mate suspects the whale's steady population growth has led to numbers higher than in the days before commercial whaling. But that idea remains debatable. Because there are no adequate records, no one can say how many gray whales plied the Pacific before whalers started killing them. Estimates range from 15,000 to 75,000 animals.

Other whale scientists dispute Mate's theory. Scientists who study another population of gray whales in the Western Pacific, near Japan, have also seen starvation. With fewer than 100 animals, the western population is too small for overpopulation to be blamed for starvation.

Peculiar behavior by the whales also suggests that the food chain itself is out of whack. Whales have been seen in unusual places—for example, in the mouth of the Sacramento River—possibly seeking new feeding grounds. Many are also delaying their trip back to Baja and staying north where the food is. The behemoths also have been seen skimming the surface with their baleen for krill as they migrate—a behavior common to blue and humpback whales but relatively rare in grays.

"They're shifting to other kinds of food we haven't seen them eat before," Mate said.

Ray Highsmith may be able to answer such questions. He will return to those rich feeding grounds—known as gray whale heaven—by boat at the end of this month. On his last trips there, from 1986 to 1988, he found amphipod numbers were on the decline and suggested that the whales might exhaust the food supply by 2002. Now he's checking to see whether he was right. If he finds plenty of the crustaceans, whale overeating is not the problem. If the sea floor is barren, that could be because of whales—or because of something bigger, like global warming.

Warming trends, whether caused by human-induced climate change or by local shifts in ocean and atmospheric patterns, are known to alter the ice patterns and ocean currents that produce plankton and transport it through the water column. Amphipods are not mobile and rely on these currents to bring them dinner. They lie on their backs on top of their tubes and wave their little appendages to direct plankton into their mouths. "If anything interrupts the import or production of food," Highsmith said, "there's a problem."

In the last five decades, much of the ice that covers Arctic waters has melted. It is not yet clear how this is affecting whales. While some scientists worry that the lack of ice disrupts the food web, others say a lack of ice is good for whales because it allows the whales, which need to reach the surface to breathe, more room to forage.

Even though the Arctic has been warming on average, some spots within the Arctic, paradoxically, are colder than usual. In some areas, the late spring ice has been slow to recede, keeping whales from reaching accustomed feeding grounds.

Perryman has linked poor health and low calf production in whales to years when lingering sheet ice has kept animals from getting an early start on feeding. Females in particular need to build up fat reserves to maintain pregnancy and milk-guzzling calves during their migration.

"Lactating and fasting at the same time is very challenging," Perryman said. "If a female is not putting on weight rapidly, she kicks into miscarriage."

Perryman has noted the pattern for five years. Two years ago, Perryman and his crew sighted just 96 calves heading north with their moms. Last year, it was 87. This year, after studying satellite images of ice distribution, Perryman predicted the calf population would bounce back. Daily calf counts show he may be right.

As in previous years, the painstaking count continued 12 hours a day, from March to June. Richard Rowlett and other researchers took shifts scanning the horizon from a cliff top on a finger of land called Piedras Blancas, which extends into the ocean near San Simeon's Hearst Castle.

Scientists believe this is the best place on the West Coast to see mothers and calves slalom through offshore rocks and kelp beds. The calf remains on the inside, closer to shore. The mother shields her offspring with her massive bulk, a precaution against marauding bands of killer whales eager to make a meal of a baby gray fattened by mother's milk.

"The cows and calves follow the inside track here," Rowlett said, plotting a course in the logbook after he spotted one large geyser of water, followed by the more timid breath of a calf in tow. He labeled the pair No. 286. "Sometimes they come so close you cannot see them over the ice plant on the cliff," he said. "You can hear them breathe and sometimes see the spray of their blow."

Completed earlier this month, the West Coast calf census this year tallied 302 pairs of mothers and offspring, an encouraging rebound after three dismal years.

The head count suggests that the total number of calves born this year is 850. This is still a preliminary number, warns Perryman, who works out such figures only after adding in estimates of how many whales travel unseen at night or offshore.

A similar census of the entire herd is conducted near Carmel. Whale counters led by a National Marine Fisheries Service biologist, Dave Rugh, tallied 2,800 whales migrating south during 532 hours of systematic searching from December to March. That count formed the basis for the preliminary estimate of 17,414.

Scientists acknowledge that counts can fluctuate, depending on observers, weather conditions and other factors.

"We've had five weird years," said Alisa Schulman-Janiger, who directs a gray whale census from the Palos Verdes Peninsula for the American Cetacean Society.

After years of spotting skinny whales, mothers without their calves, whales eating strange new foods, she was heartened to see whales back to normal, "fat and sassy" with calves in tow. She's still anxious about what next year's migration will bring.

"It's extremely important," she said, "to keep an eye on them."

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Gray Whale watching in Big Sur California, eschrichtius robustus

Gray Whale watching in Big Sur California, eschrichtius robustus
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