Steller Sea Lion Research

Steller sea lion research in Alaska, Oregon, and California.

Steller sea lion rookery

Steller sea lions at rookery.

Under Federal Law (Endangered Species Act and Marine Mammal Protection Act), NOAA Fisheries is mandated to monitor the two distinct population segments of Steller sea lions, the Eastern and Western populations.

The Eastern Population ranges east of 144°W longitudinal line (just east of Prince William Sound, Alaska) through southeast Alaska, Canada, and the west coast of the contiguous United States.

Steller Sea Lion research map
Generalized distribution (crosshatched area) of Steller sea lions in the North Pacific and major U.S. haulouts and rookeries (50 CFR 226.202, 27 August 1993), as well as active Asian and Canadian (British Columbia) haulouts and rookeries (points: Burkanov and Loughlin 2005; S. Majewski, Fisheries and Oceans Canada, pers. comm.).  Black dashed line (144°W) indicates stock boundary (Loughlin 1997) and solid black line delineates U.S. Exclusive Economic Zone.

The Western Population ranges west from the 144°W longitudinal line through the Gulf of Alaska, Aleutian Islands, and beyond the U.S. border through Russia and Japan. This population has been on the Endangered Species list since 1997.

Continued research on abundance, movements and vital rates, and diet and foraging behavior helps us understand the role of Steller sea lions in the marine ecosystem and inform management decisions for the conservation of this important species.

    Estimating Steller Sea Lion Abundance

     

    Estimating the abundance, or number of Steller sea lions in the populations, can be difficult for such a wide-ranging species. Each year, during the summer breeding season, we conduct aerial, ship, and land-based surveys to collect counts of sea lions on land. We use these data in computer models to create stock assessments.

    Steller sea lion researchers
    Steller sea lion researchers surveying rookery. 

    Studying Steller Sea Lion Movements and Vital Rates: How They Live, Breed, and Grow 

    We permanently mark a very small portion of sea lions so that we may monitor these individuals throughout their lifetime. We use this information to learn how long sea lions live, how often females give birth to young (or “pups”), and if sea lions move from their natal region, or area they were born. This information, along with other studies investigating health and disease, help us understand the overall condition of sea lions in different regions across the range of the species.

    You can help biologists look for these marked animals on Steller Watch!

    Steller Sea Lion Diet and Foraging Behavior

    There are many ways we can research Steller sea lion diet and foraging behavior—where sea lions go while at-sea, and how deep they dive, to catch their food, or “prey.” One of the most common ways is collect their scat, or feces, on land. We can use the hard parts (like fish bones) left behind to identify their prey and size of prey. We also use satellite transmitters, or tags, that are glued onto a small number of individuals to track their movements and dive characteristics to understand important foraging areas.

    Steller sea lion, - Credit:  NOAA Fisheries/Kathryn Sweeney.
    Steller sea lion with a satellite transmitter glued to its head.  This “tag” technology allows us to track sea lion movements over short periods of time.

    • Tom Gelatt, Program Manager, Alaska Ecosystems Program
    • Robert Delong, Program Manager, California Current Ecosystem Program