Researchers say whaling altered the food chain

Jim Estes clearly remembers the day when he peered down from a skiff in Alaska's Aleutian Islands and saw what looked like "The Invasion of the Sea Urchins."

The spiny round blobs had eaten right through the underwater kelp forest that shelters many marine creatures. Normally rare except in deeper waters, the urchins were jostling for space almost up to the beach.

"There were just urchins everywhere," said Estes, a researcher with the U.S. Geological Survey in Santa Cruz, Calif. "I was astonished. I just saw lots of urchins where I had not seen them in the past."

For years, Estes had been trying to figure out why the sea otters of western Alaska, which feed heavily on urchins, were disappearing. When he saw the urchin explosion, the researcher knew instantly the otters weren't dying from lack of food.

That realization and another five years of scientific work led to publication of a study scheduled for release today that sets forth a radical and potentially important new idea: An ecological chain reaction dating to industrial-scale hunting of whales in the North Pacific a half-century ago has driven the widespread decline of Alaskan seals, sea lions and otters that have puzzled scientists for decades.

The killing of whales caused a collapse in the food chain, the scientists believe. As a half-million whales were wiped out by Japanese and Russian whaling fleets after World War II, killer whales that once preyed on the larger "great" whales had to look for other food to eat.

So, the scientists theorize, some of the killer whales turned to seals instead. But before whaling, seals were never as numerous as whales. And it takes lots of seals to equal the calories in a single great whale.

It wasn't long before most of the seals were eaten up and the killer whales -- also known as orcas -- turned their attention to Steller's sea lions. Then, when those grew rare enough, they went after otters.

"If our hypothesis is correct, either wholly or in significant part, commercial whaling in the North Pacific Ocean set off one of the longest and most complex ecological chain reactions ever described," says the paper being published online in the Proceedings of the National Academy of Sciences.

Without otters to eat them, sea urchins proliferated. Urchins, in turn, hammered kelp forests just off the Alaskan coast.

The new hypothesis argues strongly against environmentalists' longtime contention that a Seattle-based fishing fleet set to catch a little over 3 billion pounds of Alaskan pollock this year has fueled the decline of sea lions by stealing their food. The pollock fishery, the nation's largest, provides the fish used in sandwiches at Burger King and McDonald's and other fast-food outlets, as well as much of the imitation crab consumed in this country.

The paper, Estes said, carries a message for those trying to manage fisheries one species at a time:

"Food webs are way more complicated than that, and when you take a species out ... it's going to have effects on a number of different things, many of which are impossible to imagine," Estes said.

The theory could revolutionize scientists' evaluation of the Bering Sea and the Gulf of Alaska, which have seen puzzling declines in some species and increases in others.

However, the authors acknowledge that so far they haven't proved anything, and that there are other potential explanations for the crashes in numbers of seals, sea lions and otters. It's also possible that their theory only partially explains the collapses, and that other factors such as fishing and climate change also are at work, said the authors and some of their critics.

Still, Estes said: "There's quite a bit of evidence that is consistent with this explanation. I'm not positive, but I think it's reasonably compelling in my mind that this is what happened."

The paper points out that killer whales today are a lot more common than scientists once thought. It wasn't until 1994 that researchers first counted them across a large range of Alaskan waters, and it took several years to compile that data.

At the same time, researchers were watching otter populations plummet. A key clue to the fact that the otters were being eaten by killer whales was that, although they were disappearing, no one was finding lots of otter carcasses.

But researchers did see killer whales eating otters. And, while no one was carefully studying the matter in the 1970s and '80s, people remembered a similar pattern: No carcasses, just plummeting numbers.

As the researchers counted up how many killer whales cruise the Bering Sea and Gulf of Alaska, and the numbers of seals and sea lions and otters and their caloric values, they found that a shift of less than 1 percent in killer whales' diet could account for the declines.

The new interpretation isn't as radical as it first sounds, the authors say. Scientists have long argued that the New World's earliest aboriginal hunters wiped out mastodons and other large animals. And scientists are finding out that in just the last century or so, killing off of wolves in the Rockies allowed elk to proliferate, and they munched down lots of trees.

If the theory about whaling is correct, it remains unclear what the implications are for modern-day officials deciding, for example, how to manage Alaskan fisheries.

"We're not advocating controlling the population of killer whales," said Alan Springer of the University of Alaska-Fairbanks, lead author of the paper. "The lesson is that it advocates a precautionary approach whether you're fishing whales or finfish or crabs or whatever."

Doug DeMaster, director of the National Marine Fisheries Service's Alaska Fisheries Science Center, said he fears some people will interpret the new theory as explaining all the population swings.

"It's pretty clear it's not just one factor that's driving dynamics of large marine mammals in the high latitudes. It's pretty clear there's multiple factors," DeMaster said. "Climate change is an important piece, as well as subsistence harvest and fisheries and a lot of other things."

DeMaster also questions to what degree killer whales ever relied on the great whales as a food source.

But the research team behind the new paper dug up an 1874 history of the whaling industry that said the term "killer whales" originated with whalers, who first called them "whale killers."

"This is a speculative study that will require a lot more research to either refute or accept," DeMaster said.

And critics of the new theory wonder: Why haven't the killer whales shifted back to eating more whales as the larger whales' populations have rebounded to varying degrees in the '90s?

The answer from the authors of the new paper: Maybe they have, at least to some degree. Springer and his co-authors say the fact that no one documented killer whales eating larger whales or seals or sea lions doesn't mean it didn't happen.

"In the Atlantic, no one has ever seen humpback whales copulate, but there is no doubt that they do it," Springer said.

The new paper is attracting support among some longtime observers of ocean trends.

"It's a circumstantial argument, but it's a circumstantial argument that ties together a lot of loose ends that the alternative explanations don't tie together, and it makes sense," said Jeremy Jackson, a scientist at the Scripps Institution of Oceanography in La Jolla, Calif. "This is a really important paper, because it exposes the complexity that we need to address if we're going to manage and protect marine ecosystems in a realistic way."

Estes, thinking back to his day on the skiff at Adak Island, says he doesn't blame the Japanese and Russian whalers for doing what they did.

"There's no way someone could have looked forward from the early 1940s and said this is going to happen," Estes said. "They would have locked them up."

P-I reporter Robert McClure can be reached at 206-448-8092 or robertmcclure@seattlepi.com

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