UC Marine Council

For California sea lions (Zalophus californianus), a dominant species on the California coast, understanding foraging is essential for understanding impact of population growth on the coastal environment. California sea lion numbers have increased steadily at a rate of 5% from the mid 1970's to 1995. In recent years, the populations have expanded at a rate of 6.2%. The impact of this increase on the surrounding environment is not completely understood. Conversely, the conflict between fisheries and sea lions over a limited resource is evident. Negative effects are apparent on both sides, from monetary loss to potential loss of a sustainable resource for fishermen and injury to mortality for the sea lions. By locating precise feeding areas, there is the potential for wildlife managers to reduce or avoid these interactions in the future. In addition, by understanding the rate of consumption of these animals, researchers can better predict the impact on the fish stock and environment that will result as this population growth continues.

Stomach temperature technology provides a tool to better understand the foraging behavior of California sea lions. Using adult females from the Channel Islands population tagged with satellite tags, time-depth recorders, and stomach temperature telemetry, we will attempt to precisely identify when and where foraging occurs. These data will also be used to obtain an estimate of foraging efficiency (catch per unit time) and time spent foraging. These measures of foraging success will be a key factor in recognizing the impact of pinnipeds in the marine environment and promising tool to monitor population status. As California sea lion populations increase, estimates of foraging efficiency will provide valuable information to predict the current and future effects on the coastal environment.