Science Spotlight

Population biology of Steller sea lions in Russia

Steller sea lions breed along the Pacific Rim from central California to the Kuril Islands. As in western Alaska, Steller sea lion populations along the coast of far eastern Russia had declined dramatically over the last 30 years, but have been recovering in recent years. Most of the sea lions in Russia are part of the Asian genetic stock, but the rookery on Medny Island, in the Commander Islands, is in the western stock. Pup counts at the Medny Island rookery have failed to recover, similar to the situation in the western and central Aleutian Islands. In order to measure survival and reproductive rates, we use the mark-recapture method with branded Steller sea lions. We are using the demographic data collected in the Commander Islands (where SSL pup counts have been decreasing) and in the Kuril Islands (where SSL populations are increasing) over the years 2000 to 2012 to compare and contrast areas of differing population trends, using multiple hypothesis testing and model-based inference to investigate the relationships between SSL abundance trends and vital rates and prey, fishing activity and environmental conditions as well as presence of potential competitors (e.g. northern fur seals) and predators (killer whales).

Foraging Ecology of Steller sea lions and northern fur seals

To understand the relationship between foraging success and population demographics, we apply our biotelemetry tools along with other approaches to measure what, where and how much Steller sea lions eat. In one example, we studied a rookery on Lovushki Island, in the Kuril Islands of Russia, where northern fur seals breed side by side with Steller sea lions. The fur seal population has recovered from over-hunting and now outnumbers the sea lions by over 10 to 1 and is still growing, whereas the Steller sea lion population has stopped increasing. We wanted to know if the fur seals were potential competitors to the Steller sea lions. Fish bones in scats tell us what the seals and sea lions ate in the last day or two, chemicals in the blubber tell us what they ate over the last few months, and chemicals in a whisker can give us an indication of what they fed on all the way back to when they were born.  

We catch Steller sea lions by darting them with a tranquilizer and then anesthetizing them with gas anesthesia. Then we can attach satellite tags that tell us where they go to feed and how deep they dive. In collaboration with Dr. Randy Davis and Ph.D. student Paul Olivier from Texas A&M University, we attached head-mounted video cameras to adult female Steller sea lions. In the images below you see Dr. Andrews adjusting the camera system on an anesthetized sea lion, and the images to the right are screen captures from a free-ranging Steller sea lion video, showing that they fed on many different prey, including octopus and salmon, although as with our results from scats and biochemical analyses, Atka mackerel was the primary prey. 

In collaboration with the National Geographic Remote Imaging Program, we also attached “Crittercam” video systems to the backs of adult female northern fur seals. Here’s a screen capture from the video, catching a seal in the act of slurping up a small silvery fish called a northern smooth-tongue. We found that adult female northern fur seals usually feed on these small prey, far from the rookery, whereas adult female Steller sea lions mostly feed on large Atka mackerel close to the rookery, but juvenile fur seals often feed on the same thing in the same place as Steller sea lions, so competition could be a problem on this rookery. 

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