Rapid declines of seabirds in Alaska linked to disappearing prey

CORVALLIS, Ore. – Some seabird species are declining at a significant rate due to lack of prey in Alaska’s Prince William Sound, according to a new Oregon State University study.

Nearly half of the marine bird species that spend their summers in the Sound experienced “biologically significant” decreases in their abundance between 1989 and 2012. These include tufted puffins and marbled murrelets–two birds that are gradually disappearing elsewhere in the northern Pacific.

For his master’s degree research in wildlife science, Dan Cushing used boat-based surveys to evaluate long-term patterns of change in the marine bird community of Prince William Sound. A research team led by Cushing found a recurring theme: species that feed on fish and krill found in waters farther from shore experienced the largest decreases.

Cushing and his advisor, Dan Roby, professor of wildlife ecology in OSU’s College of Agricultural Sciences, worked with Anchorage-based David Irons of the U.S. Fish and Wildlife Service to publish their findings in the journal Deep-Sea Research Part II: Topical Studies in Oceanography: Patterns of distribution, abundance, and change over time in a subarctic marine bird community.

“We think the most likely explanation for these changes in marine bird populations is reduced availability of key prey species,” Cushing said. “There’s also evidence that diets of some marine birds have shifted, suggesting less availability of forage fish than in the past.”

For example, the Prince William Sound stock of herring–an important prey species for seabirds–collapsed in 1993 and hasn’t recovered.

“Ocean conditions can affect plankton production and, consequently, the growth and survival of fish that feed on plankton,” Cushing said. “Populations of some of the prey species used by marine birds are sensitive to factors like ocean temperatures and the amount of freshwater discharged into the ocean, factors associated with climate change.”

The eight species or closely related species groups whose populations decreased:

• Arctic tern
• Bonaparte’s gull
• Fork-tailed storm-petrel
• Jaegers (pomarine, parasitic and long-tailed)
• Murrelets (marbled and Kittlitz’s)
• Pigeon guillemot
• Puffins (tufted and horned)
• Scoters (surf and white-winged)

Three species or species groups saw their populations increase: the great blue heron, harlequin duck and cormorants. All feed on prey in waters close to shore or on shore that is uncovered during low tide.

Roby said there is strong evidence that the declines of some marine birds in Prince William Sound are related to the Pacific Decadal Oscillation, a naturally occurring long-term climate cycle where ocean temperatures can alternate between warm and cool periods. Roby directs the U.S. Geological Survey Oregon Cooperative Fish and Wildlife Research Unit at OSU.

Many of the birds in the study were harmed by the 1989 Exxon Valdez oil spill in the Sound, but the researchers determined that the spill wasn’t directly responsible for the long-term declines of some marine bird species that persist to this day.

The Exxon Valdez Oil Spill Trustee Council, North Pacific Research Board and U.S. Fish and Wildlife Service funded the research.