"The Pribilof Island pup count is a major marker, and it was down by 4.9 percent since the 2006 count," said National Oceanic and Atmospheric Administration biologist Doug DeMaster.
The 2008 survey found an estimated 121,000 northern fur seal pups at rookeries on St. Paul and St. George islands, compared to 253,000 pups there in 1992.
"Not since 1916 have the islands produced this few seal pups," said DeMaster, director of NOAA's Alaska Fisheries Science Center.
Pelagic sealing in the open sea was banned by treaty in 1911, but commercial harvests of northern fur seals continued on their breeding islands until the 1980s, when the species was listed as depleted under terms of the Marine Mammal Protection Act.
After a period of greater regulation and population stability in the 1980s and 1990s, northern fur seal numbers began declining again 10 years ago. The Pribilof population alone has fallen by an annual rate of 5.2 percent since 1998, NOAA said.
Most northern fur seals gather each summer in the Pribilofs to rest and breed in the heart of the Bering Sea. Smaller rookeries are located on Bogoslof Island in the Aleutians and the Kuril Islands and Commander Islands near mainland Russia in the western North Pacific.
Researchers aren't sure why their numbers continue to decline, though thousands are known to drown each year in driftnets of commercial fishing vessels. Other factors that might contribute to the decline include entanglement in marine debris, parasites and disease, pollutants, predation and less nutrition, NOAA said.
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