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Steller Sea Lion Research


Male Stellar Sea Lion

The western population of Steller Sea Lions (SSL) has been in decline for several decades and is now considered endangered. There are several possible factors causing this decline, including an increase in parasites and disease, predation by killer whales, nutritional stress caused by competition with other species for food and/or changes in abundance, quality and distribution of prey, and environmental factors such as pollution and climate change. Current management efforts are focused only on commercial fishing in habitat critical to the SSL, which is thought to cause a harmful reduction in SSL prey availability.


To determine if other factors might be important in the decline of the western SSL population, NCCOS' Center for Sponsored Coastal Ocean Research (CSCOR) has been directed to conduct research focused on potential changes in predator/prey relationships in the Gulf of Alaska and the Bering Sea. This research is coordinated with NOAA Oceanic and Atmospheric Research, which is supporting studies on the potential impacts of ocean climate regime shifts on Steller Sea Lion populations. The studies are implemented through the Cooperative Institute for Arctic Research.

Predator-Prey Investigations of Killer Whales and Steller Sea Lions in Alaska - This project addresses the role that killer whale predation plays in the decline of Steller sea lions. Scientists from the North Pacific Universities Marine Mammal Research Commission will involve the local mariner community to assess knowledge of the abundance and distribution of killer whales, and initiate a photo-census to keep track of whales in the region. Direct observations of killer whale predation will estimate the impacts of predation on recovery of SSL populations. Data derived from this study will be incorporated into a model of killer whale predation, which is funded through the North Pacific Marine Mammal Research Commission.

The Role of Physiological Constraint in the Acquisition of Foraging Ability: Development of Diving Capacity in Juvenile Steller Sea Lions - This project looks at the reduction in juvenile survival as a cause of SSL population decline. It examines the diving capacity of juvenile SSLs, and how diving ability may change with development; as well as how juveniles forage and what constrains their feeding ecology. The University of Alaska will work in collaboration with the National Marine Mammal Laboratory in the collection of animals for physiological measurements. The results should allow determination of when and why juveniles are most vulnerable to ecological disturbances such as prey removal, and help identify factors that have a high probability of impacting successful recruitment.

Seasonal Assessment of Prey Competition between Steller Sea Lions and Walleye Pollock - The diets of walleye pollock and Steller Sea Lions overlap, including prey such as forage fish and juvenile pollock, yet the role of pollock as a prey competitor of SSLs has not yet been examined. This project will determine the current importance of juvenile pollock in the diet of SSLs and adult pollock to predict how the pollock population affects the population of SSLs as ocean conditions and fish communities change. Ultimately, the project could address the efficiency and effects of restricting pollock harvests inside SSL critical habitat areas.

Investigation of Foraging Behavior of Steller Sea Lions in the Vicinity of Kodiak Island, Alaska - This project will locate and quantitatively assess overwintering herring and SSL populations in the vicinity of Kodiak Island. Their distributions in the west will be compared to those in the east (Prince William Sound) during the crucial fall-winter feeding period. This will provide direct observational evidence of SSL foraging behavior, a current gap in knowledge about SSLs. NOAAs Environmental Technology Laboratory will work in collaboration with the Prince William Sound Science Center and the Alaska Department of Fish and Game on this project.

Climate-driven Bottom-up Processes and Killer Whale Abundance as Factors in Steller Sea Lion Population Trends in the Aleutian Islands - COP and NOAA's Office of Oceanographic and Atmospheric Research (OAR) are jointly funding this large, integrated ecosystem study. It comprises measurements of primary production, zooplankton distribution and abundance, and forage fish and seabird distributions. Collaboration with the National Marine Mammal Laboratory will allow determination of diet and foraging locations of SSLs, and abundance estimates and identification of killer whales in the region. These measurements will be taken in conjunction with OAR's ongoing physical and nutrient measurements by the NOAA Pacific Marine Environmental Laboratory. Comparisons of two regions, the Seguam-Amukta Pass area where SSL populations are in decline and the Akutan-Unimak Pass area where they are stable, will provide insight into the physical and biological factors affecting SSL population decline. The study will provide the first comprehensive investigation of the ecosystem supporting SSLs in critical habitat areas.

For more information:

Elizabeth Turner
CSCOR/Coastal Ocean Program
phone: 301-713-3338

Last Updated: May 15, 2003