Scientists Seek Reasons For Orca Decline
Sept. 6, 2001 -- 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."
Salmon runs have declined in most areas, and died out completely in others, and that has forced the whales to look elsewhere for food. What she suspects is they are finding it in the wrong place, on the bottom of the sea. If there aren't enough salmon to go around, the whales are probably eating a lot more bottom fish, which tend to have even higher concentrations of PCBs, she says. It also requires "a greater expenditure of energy" to dive to the depths where the bottom fish are found, thus pumping up the demand for food. And a mature orca can require 300 pounds of food per day.
It appears that the whales aren't finding enough salmon so they are being forced to dive for less satisfying food, and they are getting loaded with toxic chemicals.
"They're getting hit with a triple whammy," she says.
Dead Whale Offers Clues
Much of the evidence for that comes from an autopsy on a dead orca found in March of 2000. It had quite a story to tell.
"He was a 22-year-old male, and his body was ravaged with bacterial infection that he should have been able to fight off," she says. "It just completely got into every organ of his body and killed him."
Scientists think toxic chemicals did so much damage to the whale's immune system that it simply couldn't fight back what probably started out as a common cold.
Unfortunately, that's the only dead orca that has been found, she adds, leaving the scientists in the uncomfortable position of relying on "a sample size of one." It might seem like a dead whale should be a pretty easy thing to find, but the fact is "they don't just float up," Hawks-Johnson says.
The orcas of the Pacific Northwest are so closely monitored that if a missing whale turned up in the wrong pod, it would be immediately identified. The whales that are missing from the southern Puget Sound pods have never turned up anywhere, according to professional whale watchers, so they are presumed dead.
The new study launched by the University of Washington will seek to fill in some of the many gaps in what we know about the behavior of killer whales. Scientists will track the whales with a six-foot-long radio-controlled catamaran that is equipped with a fish finder that should tell if the whales are indeed getting most of their food from the bottom of the sea.
That will be useful along the coast of Washington, but the whales go somewhere else during the winter, and no one is certain where.
"Perhaps the most serious problem is what is happening offshore in the winter," says David Bain, an animal behaviorist who has studied orcas for 20 years. He dreams of building a robotic vessel that could follow the whales throughout the year.
In the meantime, scientists will rely on a tiny but well endowed catamaran to peer below the surface and eavesdrop on some magnificent animals that are in a great deal of trouble.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.