Project Description
A long-term goal of the San Miguel Island Research program is to understand how space and food resources are partitioned among the different age, sex and reproductive classes of pinnipeds and how behavior changes with population trends and environmental changes. Recently, juvenile survival has been identified as the an important driver of the population dynamics of California sea lions and a study of juvenile foraging behavior was undertaken at San Miguel Island to identify factors influencing juvenile survival. This study has shown that juvenile sea lions remain close to the breeding islands when young but then increase their foraging radius with age. Studies of adult females at the two largest colonies, San Nicolas and San Miguel Islands, show a significant segregation in foraging areas by adult females. In this study, we will instrument 10 juvenile sea lions at San Nicolas Island to determine if they forage in different areas from the adult females and if they show a similar pattern to juveniles at San Miguel Island in the development of their foraging behavior.
Issues & Justification
The California sea lion population has been increasing for the past three decades and now numbers in excess of 230,000 animals in U.S. waters. The population is also believed to be within the range of OSP and approaching carrying capacity. The high population levels probably have lead to competition for food among animals at each of the large island rookeries. Juvenile survival appears to be the primary driver of the population dynamics of California sea lions. Thus it is important to know habitat requirements for juveniles at the major colonies. The foraging home ranges of juveniles appear to be different from adult females when they are young but then become more similar to adults with age. This study will define the home range of juvenile sea lions at the second largest rookery of California sea lions and compare it to that of adult females from San Nicolas Island and adult females and juveniles at San Miguel Island, the largest colony. This study will provide baseline information on how changes in environmental conditions and population trends influence juvenile foraging behavior and therefore, juvenile survival.
Goals
- Describe the home range of juvenile sea lions at San Nicolas Island and compare to that of adult females at San Nicolas Island and to juveniles at San Miguel Island.
Methods
Ten juveniles will be instrumented with satellite tags on San Nicloas Island in November 2008. Scat samples will be collected at the time of deployment to assess for feeding habits of animals from the rookery at the time the instruments are deployed.