Western Steller sea lions are listed as endangered under the Endangered Species Act of the United States.  Therefore, it is important to learn about their behavior and population dynamics in ways that will cause minimal disturbance.  Population vital rates such as reproduction and survival are the primary drivers for population trends.  By understanding the causes of variation in these vital rates, we can gain a better understanding of the ultimate factors affecting the population, whether it may be food availability, disease, or killer whale predation.  For example, aspects of maternal behavior, such as how much time mature females spend at sea foraging and how much time they spend on shore nursing their pups, may provide clues as to why reproduction or juvenile survival may be reduced in some years.