Scientists Seek Reasons For Orca Decline

When you see them in the wild, they look indestructible. A male orca can weigh up to 11,000 pounds, and they have been known to eat just about everything from fish to other whales.

So with the abundance of the sea at their disposal, killer whales, which are actually more akin to dolphins than other whales, would seem to have little to fear. Except, perhaps, the one creature it's never been know to feed on — humans.

Young Whales Dying

The fact is the water's getting a little rough for the killer whale, which is found in every sea from the Arctic to Antarctica. In one area, Washington state's southern Puget Sound, the resident population of orcas has dropped 20 percent over the past five years, prompting the federal government to consider adding it to the endangered species list.

Scientists say no one knows for sure just what's going on with the three pods of orcas that make up that population. But the number of animals has dropped from 97 to 78 in just five years, and seven were lost last year alone.

"What's really worrisome is we're losing what are supposed to be the healthiest animals," says Stefanie Hawks-Johnson, a doctoral candidate in animal behavior at the University of Washington, who is heading up a multi-year effort to find out what is killing off the orcas. It isn't just that the old folks are dying off, she says. It's the younger ones, in their early 20s, at the height of their reproductive capability, that are disappearing.

That doesn't mean the killer whale, as a species, is dying out, but the fact that three pods in one area are in so much trouble is of great concern to whale experts. One of the pods has not produced a calf since 1996.

Although the exact cause is still a mystery, the evidence at hand suggests that a number of factors are contributing to a biological domino effect. Primary suspects are declining salmon runs, the preferred diet of these particular orcas, and poison from a number of industrial compounds that have been banned for years.

PCBs, DDT Passed Through Food Chains

Of particular concern are polychlorinated biphenyls, or PCBs, and the pesticide DDT. The National Marine Fisheries Service reported recently that these banned substances were found in juvenile salmon studied over the past three years. Concentrations were high enough to damage fish immune systems, the agency says, and that toxicity could be passed up the food chain to other creatures — including orcas — that eat the salmon. The agency also says it isn't clear yet whether the chemicals can also be harmful to humans who eat the contaminated fish.

But that's just part of the problem, Hawks-Johnson says. She took a break from her graduate studies to work as a naturalist on a tour boat operated by a company called the Mosquito Fleet over the past few years, and that gave her plenty of chances to observe the orca's lifestyle.

"Common sense tells me what's going on," she says. "These animals don't have enough food."

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