Wildlife researchers are crowdsourcing the task of whittling down a half-million photos captured at Steller sea lion sites in the western Aleutian Islands over the past year or so. Biologists will use the smaller selection of pictures to help determine why the region's sea lion population continues to decline.

The Steller sea lion population in the westernmost islands has fallen 94 percent in the past three decades, according to the National Oceanic and Atmospheric Administration. Many potential causes of the decline have already been ruled out, but researchers still don't know why it's happening.

"We wanted more of an effort out there because the western Aleutian Islands is where we're seeing the most significant (population) decline," said NOAA fish biologist Katie Sweeney, who is leading the project.

Scientists recognize the species as two distinct stocks, western and eastern, with the western stock listed as endangered under the Endangered Species Act.

Sea lion populations in Alaska have mostly rebounded, but not around the remote islands, according to NOAA. The agency says about 7,200 pups were born in the western Aleutian islands between 2011 and 2016.

The agency's Alaska Fisheries Science Center named its first-ever crowdsourced project "Steller Watch." People began sifting through images Wednesday morning taken at six different sites on five Aleutian islands. The sites are between the nation's westernmost island of Attu and Ulak Island.

Steller sea lion pups, approximately a month old, spotted playing in pools on Ulak Island (NOAA Fisheries)
Steller sea lion pups, approximately a month old, spotted playing in pools on Ulak Island (NOAA Fisheries)

Placing the cameras was necessary for keeping tabs on the pinnipeds since the islands are not easily accessible. Sweeney said she and others head out to the islands about once every other year.

Images are captured every 10 to 30 minutes during daytime at the sites, Sweeney said. That yielded nearly 380,000 photos in the past year alone.

"It was just hard to keep up with the demand," Sweeny said.

Nearly 1,800 volunteers stepped up on the first day, classifying about 30 percent of 30,000 images accessible on the website. Sweeney said her team chose to start out with only a portion of the pictures; she didn't know if people would be interested in helping out, but the initial, immediate response suggests otherwise.

Currently, the participants are simply asked if they can see Steller sea lions in the photos, and if weather obscures the shots, among other basic prompts. The next phase will involve identifying sea lions that previously have been branded by scientists.

Aerial view captured by a hexacopter showing a previously marked male, M539 (NOAA Fisheries)
Aerial view captured by a hexacopter showing a previously marked male, M539 (NOAA Fisheries)

"Hot branding" started in 2011 in the region, Sweeney said. Young sea lions are sedated and then branded, she said. Over a five-year period, NOAA marked 265 pups, less than 4 percent of the western Aleutian Islands population.

"With the sightings of these marked animals, eventually if we get enough years of data, we can estimate the survival rates and see if there are differences between male and females, or among ages, and other factors," Sweeney said.

"There are important parameters we have to figure out before we can get a better idea of why this population continues to decline," she said.