A Puzzle In the Pribilofs- page 2 | Science | Smithsonian

A Puzzle In the Pribilofs

On the remote Alaskan archipelago, scientists and Aleuts are trying to find the causes of a worrisome decline in fur seals

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Though the Pribilof seals are falling in number, they are not in danger of extinction—at least not yet. In 1988, fur seals were listed as “depleted” under the federal Marine Mammal Protection Act. Since 1998, the number born on Pribilof beaches has dropped almost 6 percent a year, compounding a trend that has continued off and on for half a century. And they aren’t the only Alaska marine animals showing signs of drops. Steller’s sea lions have crashed by 80 percent since the 1970s; sea otters have almost disappeared from the Aleutians. Certain seabirds have plummeted too, and fish stocks are changing.

“Going back into the 1950s and ’60s, it’s all part of one larger decline that’s not really well understood,” says Rolf Ream, a zoologist at the National Marine Mammal Laboratory in Seattle. “There really is no reason that it should be continuing, and what’s really more shocking is that it hasn’t shown any sign of recovery. There are just very few ideas, and part of the problem is that we really don’t have a lot of the data we need.”

The northern fur seal, Callorhinus ursinus, is a cousin to eight other fur seal species found mainly in the Southern Hemisphere. Along with five types of sea lions—closely related animals with large bodies, coarser fur and more rounded snouts—this gregarious, harem-building marine predator belongs to the Otariidae family, thought to have diverged from a bearlike terrestrial ancestor about 25 million years ago. Unlike true seals, such as the harbor and ringed species, the Otariidae sport external ears and the ability to rotate hind flippers forward beneath their bodies so they can walk and climb on land. Females can live a quarter-century or more, while males rarely live beyond 16 or 17.

Like other herd-dwelling pinnipeds, fur seals follow a yearly cycle that begins in May when the 450- to 600-pound bulls return to the rookery to stake out prime breeding turf. The much smaller adult females return in June and usually within two days, give birth to a single 10- to 14-pound pup. Within a week, the adults mate. For nearly two months, the largest and most dominant bulls fight bloody, bellowing battles to defend their territories and keep other bulls away. During that time, the rookery takes on a complex structure that a researcher must carefully navigate in order to collect dead pups for study and to avoid the dangerous kings of the shore. By October, the pups begin to wean. About the same time, the seals start to scatter, with females, pups and juveniles migrating farthest, south of the Aleutian chain into the North Pacific.

Intelligent and at times aggressive, fur seals are agile on both sea and shore. But their most remarkable characteristic almost led to their demise: their dense waterproof underfur. The pursuit of this luxurious pelt by Russian and American traders in the 18th and 19th centuries twice pushed the seals to the edge of extinction. Between the early 1890s and 1909, an average of about 33,000 seals were killed each year in the Bering Sea, most of them females foraging for food. The U.S. commercial harvest alone (probably in excess of $200 million from the late 1860s to 1984) repaid Alaska’s $7.2 million purchase price 28 times over.

Then, almost a century ago, estimates that only 200,000 to 300,000 fur seals remained in the world mobilized conservationists and inspired the first international effort by governments to protect marine life. In 1911, the United States, Great Britain (acting for Canada), Japan and Russia signed the Treaty for the Preservation and Protection of Fur Seals and Sea Otters. It prohibited killing seals at sea except by Indians, Aleuts and other aborigines using primitive weapons. Congress halted all onshore hunting of seals on the Pribilof Islands between 1912 and 1917 except for subsistence hunting by local Natives. The animals rebounded at a tremendous rate, and the U.S. government reinstated an annual harvest on land, which ranged from about 34,890 seals in 1918 to 95,000 in 1941.

That year, Japan pulled out of the treaty, arguing, in part, that the seals had grown so numerous that they had begun to harm Japanese fisheries, but in 1957 the four original signatories ratified a new treaty. At that time, U.S. biologists successfully argued that cutting the number of female seals would decrease the age when the animals first became pregnant, contributing to an increase in pup numbers and survival. About 300,000 Pribilof females were killed between 1956 and 1968 on land, and another 16,000 were taken at sea for research between 1958 and 1974.

But the herd didn’t respond as expected, and the population began to slide. Even after the female take ceased, numbers kept trending down, and government biologists ended the commercial harvests on St. George in 1973 and began a long-term program to monitor the island. A ferocious public campaign against killing the seals, combined with shrinking markets for their fur and the lapse of the 1957 treaty, would end the commercial harvest altogether in the Pribilofs by 1984. Native residents have since been allowed to kill a small number of juvenile male seals for food.

Once the industrial harvest ended, funding for the study of these mammals plummeted. In 2004, the National Marine Mammal Lab—charged with conducting a census of the population and monitoring its status—had virtually no budget for fur seal research. “We call it the ‘Pribilof Islands Program,’ but it’s just me handling the management end and Rolf [Ream] and his bunch from the lab doing the research,” says Dave Cormany, who administers the program from Anchorage with long visits to St. Paul.

Sorting out possible explanations for the fur seal decline is as difficult as disentangling the fishing nets that often snag driftwood and entrap overcurious pups. Scientists have speculated that development of new harbors and industry on St. Paul may be disturbing seals. Competition with commercial fishing is another possibility, especially since seals forage in many of the same areas as the pollock fleet. But commercial species like pollock remain high in the Bering Sea, and it’s not clear how fishing might be taking food from the seals. Confounding it all, even as their numbers keep falling, the seals that do return to the Pribilofs appear healthy. “We’re sitting up here and we’re seeing animals, and they seem to be in decent condition, and I haven’t seen a change in that,” says Ream, who has been working in the Pribilofs for 16 seasons. “We don’t see them in winter, but they tend to be showing up fine. I mean, there are a lot of fat pups out there.”


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