Jan. 22, 2003 Archaeological evidence from prehistoric hunters in Washington and Alaska adds new fuel to the ongoing debate over the belief that humans have a propensity to over-exploit their natural resources, and also indicates that early Indians' harvest of northern fur seals was sustainable.
"The research clearly indicates that over-exploitation is not a universal characteristic of subsistence economies," said Michael Etnier, who earned his doctorate in anthropology from the University of Washington last month. His work also reveals evidence of previously unknown rookeries, or breeding colonies, of the seals (Callorhinus ursinus) on or near the Washington coast and on or near the Alaskan Peninsula. The findings come from his not-yet-published doctoral dissertation.
Etnier's results have potentially important implications for managing the seals, which were heavily hunted for their fur beginning in the late 18th century. The United States' purchase of Alaska in 1867 was prompted in part by the desire to control the lucrative fur seal trade. The animals have been studied and managed for more than 150 years, first by Russia and then the United States.
Northern fur seals are large marine mammals (mature males can weigh between 700 and 800 pounds) whose current range is largely restricted to high latitudes of the North Pacific Ocean. The animals spend most of their lives at sea, but breed and give birth to their pups on land. The largest rookeries of northern fur seals are in Alaska's Pribilof Islands in the central Bering Sea. Mature males tend to remain in the North Pacific while females and juveniles migrate perhaps as far south as Baja California. However, in 1968 a rookery was established naturally on San Miguel Island off of Santa Barbara, Calif.
Russians began commercial hunting of the animals in the late 1700s and a large colony of seals was exterminated by 1833 on the Farallon Islands off San Francisco. Recent analysis of seal bones from hunting camps on the Farallons by other researchers indicates these animals were northern fur seals, not another species, Guadalupe fur seals.
Etnier, now a contract scientist with the National Oceanic and Atmospheric Administration in Seattle, analyzed collections of seal bones previously uncovered during excavations on Umnak and Kodiak islands in Alaska and at Ozette on Washington's Olympic Peninsula. The Ozette assemblage was by far the largest, consisting of more than 60,000 seal bones recovered from an Indian village buried by mudslides. The bones were recovered from layers dated between A.D.1100 and 1800. The Alaskan sample of seal bones was smaller and less stratified, but it extended over a 3,000-year period.
By examining teeth and jawbones, Etnier was able to measure the age composition of the seals with an emphasis on finding their breeding distribution. He also was able calculate the growth rates of individual animals as a way of estimating population levels over time. Seal teeth contain growth rings similar to tree rings that scientists can count. The age of an animal also can be estimated by the size of its mandible.
The key piece of evidence from Ozette pointing toward the existence of a previously unknown rookery was the presence of bones of seal pups under the age of 4 months.
"You need the consistent presence of pups over a long time frame to eliminate the possibility of the remains coming from an animal being washed up on the shore," said Etnier. "These animals swim thousands of miles each year, so you need to find pup bones from an age when they can't swim very far. Research has shown that fur seal pups can travel 200 to 300 miles from where they were born by the time they are 4 months old. So you have to consistently find pup bones in the 0-3 month age range before you can conclude that they came directly from a rookery.
He said the 800-year fossil record shows that the people at Ozette were hunting male and female fur seals of all ages throughout this time span.
Etnier also measured individual growth rates of male fur seals, because animals tend to grow to smaller body size when their population levels are high and larger body size when their population levels are low. He compared 230 seal jaws containing teeth from Ozette with 405 animals collected in the 20th century from the Pribilof Islands. He found that Ozette seals were smaller in any age class than the Alaskan ones. At first glance this would seem to support the idea that the Ozette seals came from a relatively large population. However, Etnier said there is a second potential explanation: seals living in higher latitudes may be larger simply because they require more body insulation in colder waters. Still, the size of the Ozette animals is consistent throughout the entire 800-year sequence at Ozette, an indication that prehistoric hunting did not significantly affect fur seal populations levels over the time period he examined.
Etnier said his analysis, as well as work of other researchers pointing to other prehistoric rookeries along the coasts of British Columbia in Canada, Oregon Coast and Monterey Bay, Calif., "clearly indicates that the breeding distribution of fur seals was much more widespread than historically documented and that it appears to have been stable until the early historic period."
"All of the data I examined suggests that prehistoric exploitation of fur seals was sustainable and that all of the biogeographic changes documented for fur seals were caused relatively recently by the commercial fur trade," he said.
"However, I don't think the Ozette evidence necessarily shows that the people made a conscious decision to conserve fur seals. They were taking animals of every size and hitting the animals hard. But if you try to figure out if a particular harvesting practice represents intentional resource conservation based on the archaeological record, you start down a slippery slope."
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