November 14, 2007
"Looking at western stock trends since 2004, our surveys show mixed results--increases here and decreases there--but the overall picture indicates that the Steller sea lion population west of Cape Saint Elias in 2007 was similar in size to the population in 2004," said Director of NOAA Fisheries Service's Alaska Fisheries Science Center, Doug DeMaster. "This year's count, while incomplete, supports that big-picture impression."
Declines are more prominent in the western part of the survey area, with some gains appearing further eastward. The 2007 count in the Central Gulf of Alaska, from the central Kenai Peninsula through the Semidi Islands, is the first showing a population increase since the 1970s, when the time series began.
Researchers conduct aerial surveys for adult and juvenile Steller sea lions from mid-June through early July when the largest numbers are onshore to give birth and breed. Researchers hoped in 2007 to survey all terrestrial rookery and haul-out sites from Cape Saint Elias to Attu Island. Research flights occurred between June 9 and July 6.
Weather and aircraft mechanical problems prevented survey effort in the western Aleutian Islands and limited survey effort in the central Aleutian Islands to the eastern portion between Yunaska and Tanaga Islands, with very little effort occurring west of Amchitka Pass.
"Despite the weather and technical issues, we were still able to gather enough information to detect and reaffirm trends in the eastern and central parts of the survey area," said Lowell Fritz of the Alaska Fisheries Science Center's Alaska Ecosystem Program.
Researchers took photographs of Steller sea lions on rookeries and haul-outs using both a medium format (5-inch wide) film camera and a digital camera mounted side-by-side in the belly port of a NOAA Twin Otter aircraft. The 2007 survey was the first test of a digital camera for this use, and it performed well, according to Fritz.
Two researchers working independently counted all Steller sea lions at each terrestrial site photographed during the 2007 survey. Statistical comparisons indicated there were no significant differences between counts from the film and digital images, or between the researchers' counts.
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