Much to the horror of local harbor seals, killer whales from out of town popped into Puget Sound recently for an eight-week feast.
Eleven killer whales, each eating one or two 180-pound seals a day, polished off about half the harbor seals in Hood Canal, a deep-water finger of Puget Sound that runs along the eastern edge of the Olympic Peninsula.
By early March, the killer whales had had their fill -- about 700 harbor seals. The transient predators swam back out to the Pacific, leaving behind a deeply traumatized community of harbor seals.
"They were up on the bank quivering," said Steve Jeffries, a marine mammal biologist who works for the Washington State Department of Fish and Wildlife
Puget Sound harbor seals are not quivering alone. Killer whales, a beloved icon of the environmentalist movement, may be on a species-threatening rampage.
In the past 15 years, killer whales -- also called orcas -- have wiped out entire populations of sea otters on some of the Aleutian Islands in Alaska. They are also prime suspects in the otherwise unexplained disappearance in the past 30 years of 80 percent of Alaska's Steller sea lions.
According to a new theory of killer whale predation, the highly intelligent, pack-hunting creatures have been forced by man to change their dining habits and are voraciously killing a cascade of mammalian prey from the North Pacific to Antarctica. Over the past 50 years, according to the theory, killer whales have caused sequential worldwide declines in the population of various seals, sea lions, minke whales and sea otters.
The predation theory, which is the focus of a meeting this weekend of more than 50 marine scientists in Santa Cruz, Calif., blames the destructively changing tastes of killer whales on industrial whaling.
By its peak in the early 1950s, before international bans, highly mechanized whaling had reduced most species of big whales to a fraction of their historical numbers. In the North Pacific and southern Bering Sea prior to whaling, the gross estimate of whale biomass was about 30 million tons. By the time whaling ended, 3 million tons of living whale remained.
"When that happened, some killer whales, which had been preying on big whales, had to do other things to make a living," said James A. Estes, a research scientist in Santa Cruz for the U.S. Geological Survey and an originator of the theory that whaling forced some killer whales into novel eating habits.
"When the number of prey was insufficient to satisfy them -- they do eat a lot -- they moved on to something else and they did it in a sequential way," said Estes, who concedes that the predation hypothesis is speculative. "My gut feeling is that it is right, but it could very well be wrong."
The precipitous decline of sea otters in some parts of Alaska is the best-documented case of nouvelle cuisine for killer whales. It is also the most nutritionally curious. A sea otter is not particularly satisfying for a killer whale, which is the largest known predator of warm-blooded animals. Orcas are about 26 feet long, weigh 10 tons and eat about 4 percent of their body weight a day. A sea otter weighs about 40 pounds, which includes the thickest fur of any animal.
Sea otters are "dental floss" for killer whales, said Robert T. Paine, professor emeritus at the University of Washington's biology department. An orca needs to eat seven sea otters daily to fill up.
In the North Pacific, a half-century of steep sequential decline in the population of sea lions, harbor seals and sea otters "jives well" with the theory of shifting overkill on the part of killer whales, according to Alan M. Springer, a research professor at the University of Alaska's Institute of Marine Science in Fairbanks.
Researchers in Alaska have not found a decline in food or habitat -- or an increase in illegal hunting -- that explains the sudden disappearance in some areas of seals, sea lions and sea otters. There has also been a notable absence of carcasses along the Alaskan coast. Killer whales often eat smaller prey in a single gulp.
It does not take very many killer whales to ravage a large healthy population of small marine mammals, according to Springer, a marine ecologist who is presenting a paper supporting the predation theory in Santa Cruz.
"You don't have to gather all the killer whales in the North Pacific to get this to happen," he said. "A surprisingly small number -- we are talking tens of killer whales -- could have done this to the sea otters."
The killer whale world, with an estimated population of 30,000 to 80,000, is roughly divided between fish and mammal eaters. Those that eat mostly fish tend to live in resident pods, or family groups, that stay in one area. Those that eat mostly mammals tend to travel in transient pods that roam the oceans. Killer whales, the largest member of the family of oceanic dolphins, live from 50 to 80 years, and it is not uncommon for members of a pod to have hunted together for more than half a century.
In the Southern Hemisphere, where killer whales are most numerous, there has also been a sharp sequential decline in two species of marine mammals since whaling was banned in the 1950s, according to Trevor A. Branch, a graduate student at the University of Washington's School of Aquatic and Fishery Sciences.
Starting in the 1950s, he said, the number of southern elephant seals plummeted between 45 and 80 percent before stabilizing at a low level in the 1980s. At that point, the number of Antarctic minke whales (which are roughly the same size as killer whales) began to swoon, declining by about 57 percent through the 1990s.
"There is circumstantial evidence that killer whales went after elephant seals and then minke whales," said Branch, who is also presenting a paper at the conference in California.
Circumstantial evidence notwithstanding, there are many marine mammal researchers who don't buy the theory that killer whales are laying sequential waste to marine mammals worldwide.
"They are generalizing across the entire world with so little real evidence," said Craig Matkin, a marine mammal biologist from Homer, Alaska, who has studied killer whales for 20 years.
To start with, Matkin and other biologists say, there is no compelling historic evidence that a large number of killer whales were ever dependent on the large whales wiped out by industrial whaling.
Matkin said he also worries that blaming killer whales for recent sharp declines in numbers of some marine mammals will give politicians and bureaucrats an excuse not to protect coastal water quality and habitat.
"It is the Greenpeace nightmare," writes Branch, the researcher at the University of Washington. "Antarctic minke whales are the banner-waving symbol of the anti-whaling movement, but so is 'Free Willy' [a movie-version killer whale is freed from an evil marine park owner]. What do you do when one is decimating the other?"
For the scientists meeting this weekend in Santa Cruz, that question is unanswerable. No one is proposing that killer whales be killed for inappropriate eating. In any case, federal law protects all marine mammals.
"The only possible test is the future," said Estes, the scientist who has popularized the predation theory. "If we manage to save the great whales and they recover, we might see transient killer whales go away from smaller marine mammals."
In the case of the slaughtered harbor seals of Hood Canal, the killer whales may well have done an ecological good deed.
By historic standards, there are too many harbor seals inside Puget Sound, and they are feasting on endangered summer chum salmon. Since the Marine Mammal Act protects the seals, there was little that could be done to protect the salmon -- until the transient killer whales showed up for an extended meal.