The 2011 survey of endangered beluga whales in Alaska's Cook Inlet spotted 20 percent fewer animals but federal officials say it's not an indication of an abrupt population drop.
The survey, conducted in June by the National Marine Fisheries Service and announced Monday, recorded 284 of the whales, down from 340 recorded in 2010.
However, federal officials said estimates can vary depending on weather, survey conditions or changes in beluga distribution. The survey concentrates on whales' favorite locations in the upper Inlet and along the coast, lead scientist Rod Hobbs said by phone from Seattle.
The lowest number of belugas spotted was 278 in 2005. The highest in the last decade was 386 in 2001.
Year-to-year changes in population estimates are less important than the long-term trend, Hobbs said, and the latter indicates Cook Inlet belugas continue to trend downward. The numbers tracked over the last 10 years show an annual rate of decline of just more than 1 percent.
"That's the slope we get -- 1.1 percent per year," he said.
Cook Inlet stretches 180 miles from Anchorage to the Gulf of Alaska. Beluga whales, which turn white as adults, feed on salmon, smaller fish, crab, shrimp, squid and clams.
The federal government declared Cook Inlet belugas endangered in 2008, a decision fought by the state of Alaska, which contends that the listing will hurt economic development at the Port of Anchorage, the state's largest, and oil and natural gas development rigs off the Kenai Peninsula.
The Cook Inlet beluga population dwindled steadily through the 1980s and early '90s and accelerated between 1994 and 1998 when Alaska Natives harvested nearly half the remaining 650 whales in only four years. The National Marine Fisheries Service initially determined that controlling subsistence hunting would allow the population to recover. When it did not, they agency declared belugas endangered.
The listing in November was affirmed by a federal judge, who rejected the state argument that belugas already are protected by other environmental laws and that the fisheries service failed to consider state conservation programs designed to improve the habitat and food supply of belugas.
NFMS officials said the estimate compiled from two weeks of flights shows a beluga population within the range of the 10-year population trend. An actual 20 percent decrease, they said, would have been reflected in more carcasses reported.
"Only three dead belugas were reported this year, which indicates that large numbers of mortalities did not occur in 2011," said Doug DeMaster, director of the Alaska Fisheries Science Center, in the announcement. "While NOAA remains concerned that this population is not showing signs of recovery, at this time we do not believe this estimate represents a marked decrease in the population."