Wednesday, December 30, 2009

Good news, bad news, for Alaska sea lion numbers

A count of Alaska's Steller sea lion pups indicates the state's two populations are headed in different directions for recovery.
Pups in the eastern population, living along Alaska's Panhandle, are thriving.
"The eastern stock has met its recovery criteria," said Lowell Fritz, a biologist at the National Marine Mammal Laboratory in Seattle. The population may even be close to removal from the threatened species list, he said.
The western population, from Prince William Sound to the Aleutian Islands and the Bering Sea, continue to struggle.
"We expected to see the increased Steller sea lion numbers in southeast Alaska again," said Doug DeMaster, director of the Alaska Fisheries Science Center in Seattle. "The mixed results in the western population, however, indicate that some areas have improved in numbers while others continue to decline, especially the western Aleutian Islands."
Most of the world's sea lions live in Alaska. The western stock declined by 75 percent between 1976 and 1990, leading to their listing as endangered.
Disease and contaminants have diminished as suspects, Fritz said. The decline likely was due to a combination of factors, including environmental changes, nutritional stress or changes in prey compositions.
"We don't really know how to weight those," Fritz said.
Federal, university and state researchers have spent millions trying to find out. Federal wildlife managers implemented no-fishing zones around rookeries and haulouts to enhance recovery, a move questioned by Alaska's commercial fishing industry.
The eastern population, which extends from Alaska's Cape Saint Elias into California, was counted last year at between 45,000 and 51,000 animals. The population has more than doubled since it was declared threatened in 1990.
The last pup survey was done in 2005. Aerial surveys from June 24 to July 15 covered three-quarters of the western range, Fritz said. Survey sites in the western Aleutians or Pribilof Islands could not be flown and numbers from earlier years, mostly 2008, were used.
Pup production in the western population increased from 9,950 in 2005 to 11,120 this year but varied greatly by area. Pup counts increased 18 percent throughout the Gulf of Alaska and the eastern Aleutian Islands but were 6 percent lower in the central and western Aleutians.
The number of Steller sea lion pups counted southeast Alaska was 7,462. That exceeded previous counts going back to the 1960s. The new data indicate that pup production has increased at a rate of almost 4 percent per year at southeast Alaska's five major rookeries since the late 1970s.
Fritz said the surveys indicate some mingling of the populations. Recent genetic samples indicate that western females have moved to southeast Alaska and are breeding with the eastern population. Likewise, the easternmost rookery of the western population showed 200 more pups than four years ago.
"Some of that could be eastern moms moving west," Fritz said.

No comments: