Sea Lions may be slowly rebounding

November 14, 2007

Courtesy of  Far North Science
By Doug O'Harra

Steller Seal Lion
NMML photo library

But gnarly weather hampered the 2007 surveys and kept biologists from visiting some sites. Combine that difficulty with continued declines at certain central and western Aleutian locales, and the overall prognosis for the species remains very much guarded, according to a memo released this week by the National Marine Fisheries Service.

Still, this "mixed" news contrasts sharply with the precipitous plunge of the 1980s, when the number of sea lions between the Gulf of Alaska and the tip of the Aleutian chain seemed trapped in a population tumble that scientists could not explain and managers could not derail.

"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 Doug DeMaster, director of the Alaska Fisheries Science Center in a press release from NOAA Fisheries.

"This year's count, while incomplete, supports that big-picture impression."

1978: Before the decline
Sea lions on Middleton Island
NOAA photo library

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.

Even such an inconclusive finding offers good news in Alaska's epic sea lion saga, a high seas conundrum that evolved into one of the most intractable scientific problems in the history of the North Pacific marine management.

For reasons that still remain somewhat unclear and immensely complex, the western population of Steller sea lions - from the Kenai Peninsula and Kodiak to the tip of the Aleutian Chain - plunged by more than 75 percent in the 1970s and 1980s.

The decline - which may have been triggered by a colossal regime shift in ocean conditions - slowed in the 1990s and, by the early 2000s, may have begun a slow rebound.

Counts at certain rookeries and haul-outs found the first increases in a quarter century in 2002, 2004 and now, in 2007.

At the same time, hundreds of scientists from about 30 institutions and agencies embarked on an unprecedented $125 million investigation to find out why the species crashed and what factors had prevented its rebound - a Sen. Ted Stevens generated project that some have likened to a marine science moonshot.

A small part of that intense investigation are the regular counts by federal and state biologists, offering both reality check for fisheries restrictions and population data for ongoing scientific studies.

This summer researchers visited 65 of the 87 trend sites from the 1970s, and 124 of the 161 trend sites from the 1990s. Here's more detail from NOAA fisheries:

NMML photo library

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.

The official count memo with detailed statistics adds this:

Steller Seal lions under water
NMML photo library

The 2007 count in the C GULF is the first showing an increase since the beginning of the time series, and is similar in magnitude to the 2000 and 2002 counts. ...

Although counts at some trend sites are missing for both 2006 and 2007, available data indicate that the size of the adult and juvenile portion of the western Steller sea lion population throughout much of its range (Cape St. Elias to Tanaga Island, 145*-178* W) in Alaska has remained largely unchanged between 2004 (N=23,107) and 2007 (N=23,118). This conclusion was also reached following the incomplete survey of 2006.

However, there are significant regional differences in recent trends: increases between 2004 and 2007 in the E ALEU, W GULF and C GULF have largely been offset by decreases in the eastern C ALEU and E GULF.

Recent trends (through 2004 and 2006) in the western C ALEU and W ALEU have been negative, suggesting that the overall trend for the wDPS in Alaska (through 2007) is either stable or declining slightly.