closing of the circle


The Why Files covered Keiko, the killer whale, a whale of a science project, and the survival of elephants.

Population: six billion strong -- or weak?

The Why Files covers the battle between evolution and creationism.


Diving! A gray whale disappears beneath the surface.

Courtesy William Megill, Coastal Ecosystems Research Foundation.


A spyhopping gray whale.

Courtesy National Marine Mammal Laboratory. Photo by Dave Withrow, NMML.

Blood in the water
21 MAY 1999. Using a harpoon and a rifle, Makah whalers in a cedar canoe and motorboats killed a female gray whale along the northwest tip of Washington State on May 17, resuming an ancient tribal tradition after seven decades.

As they butchered the whale on the beach, members of the 1,700-member tribe washed blubber down with Coke. One leader told the Seattle Times that the event was a "closing of the circle. We are whole again."

The Makah quit subsistence whaling in the 1920s, after commercial whalers caused a worldwide scarcity of gray whales. The tribe retained whaling rights in its 1855 treaty with the U.S. government, and is permitted to kill five whales annually -- and 20 maximum -- between 1998 and 2002, by the International Whaling Commission.

gray whale

In protesting the first legal killing of a gray whale in the lower 48 states in 75 years, conservation and animal-rights groups warned that the hunt was cruel and could open the door to a resumption of commercial whaling.

The magic number
These limited indigenous hunts will not, by themselves, cause the extinction of the gray whale, which now numbers about 26,000. But The Why Files got to wondering: How many is enough? Is there a magic number that ensures survival of an animal species?

During the 1980s, conservation biologists wondered what to advise regulators about how many animals were needed to prevent extinction, and when a species should receive protection. The answer was a concept called the "minimum viable population," or MVP, which often came to 500 animals, says Douglas DeMaster, director of the National Marine Mammal Laboratory in Seattle. It was thought that having 500 animals would avoid problems with "inbreeding depression," the loss of vitality and increase in disease caused by a lack of genetic diversity. (Here's a contrarian view of inbreeding from house fly research.)

The approach has largely been abandoned, however, as the picture grew murkier. Obviously, other factors affect species survival, including habitat area and fragmentation, reproductive capacity, competition, and threats of disease, hunting and predation.

As computers continued chewing data in an effort to come up with the perfect MVP, ecologists threw a new element into the equation: the recognition that rare events like hurricanes, epidemics and fires could wipe out entire species. For example, it was difficult to enter into MVP the probability that a coastline has a 10 percent chance of experiencing a hurricane that could kill off a rare species once in every 100 years.

If populations were not really immune to extinction, the concept of "minimum viable population" lost meaning, and instead of looking for ironclad guarantees, conservation biologists spoke about probabilities of survival in "population viability analyses" that sounded vaguely like basketball wagers: "The wing-tipped attorneybird has an 80 percent chance of surviving for 500 years."

Yet the new approach has its own limitations, DeMaster says, since the calculations are "dependent on input parameters that were very difficult to estimate." (Sounds to us like garbage in, garbage out!)

This is particularly true of whales: Not only are their migration patterns and life histories poorly understood, but the effects of larger changes in the ocean are obscure. Could global warming, for example, promote disease, cut the supply of food, or cause a competitor to become more abundant?

Finally DeMaster says mathematical calculations "tend to lose general support because very few people understand (and believe in) the analysis."

How many animals are enough?
Where does that leave us? Aboriginal Siberian whalers are already permitted to harvest 600 gray whales -- without the "benefit" of TV cameras -- over five years, and the fact that the Makah are hunting a few more will not cause them to go extinct. "According to IWC [International Whaling Commission] scientists, there was no scientific concern about harvesting more than 600 gray whales over five years," says Scott Smullen, a spokesperson for the National Marine Fisheries Service.

spyhopping gray whale

In general, DeMaster says that where data are limited, a series of nested questions is often a better way to assess vulnerability to extinction. For example, he points out, the International Union for the Conservation of Nature uses questions about the number of animals in the population, trends in abundance, the number of sub-populations in a certain area, and how much the population varies from year to year. He stresses that if the answers to even these simple questions are unknown or uncertain, managers should be err on the side of conservation.

The question of how many is enough interests zoos trying to come up with survival plans for endangered species. And even if more is better, biologists are eager to try rescue plans when animals have gotten desperately scarce. The whooping crane, for example, has recovered to almost 200 birds from a low of just 15.

Back in the Northwest, televised blood on the water has polarized a conflict between indigenous whalers and advocates of whales and animal rights. In an information-age attack, the Makah web site was hacked, and protestors denounced the killing of the 30-ton female whale as the "Makah Whale Slaughter."

But on nearby Vancouver Island, Canada, a related indigenous people is interested in the cultural benefits of resuming an ancient tradition. As Francis Frank, co-chair of the Nuu-chah-nulth tribal council, told the Seattle Times, "The Makahs' success . . . certainly lays out a blueprint for us."

According to Smullen of the National Marine Fisheries Service, we are unlikely to see major increases in the amount of indigenous whaling, which now accounts for roughly 200 animals (of all species) per year. Regarding the resumption of commercial whaling -- the real cause of serious declines in whales over the past 200 years, he says, "The U.S. remains very opposed... as do a number of other IWC [International Whaling Commission] member countries. I don't see that happening."

--David Tenenbaum


The Why Files Good references on minimum viable populations:

Conservation biology: an evolutionary-ecological perspective, edited by Michael E. Soule and Bruce A. Wilcox, Sunderland, Mass: Sinauer Associates, 1980.

The Diversity of Life, Edward Wilson, Harvard University Press, 1992.

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