Project Description
Measuring foraging behavior of Steller sea lions is necessary to define important foraging areas, provide data to test among multiple hypotheses for declines and lack of recovery, and to evaluate the efficacy of critical habitat and fisheries management measures. Because of concerns about decreased juvenile survival, during 2000-2005 field studies focused on measuring foraging behavior of juvenile age classes using a variety of satellite-linked dive recording telemetry instruments. Although much of the tracking information has been published, data collected on the physiology and health of juveniles during that period will continue to be analyzed. Field studies must now focus on improving our understanding of the foraging behavior of older animals, in particular of adult females. However, FY07 plans to capture and instrument older age classes by use of either floating pens or at-sea by developing a ship-deployable net were cancelled due to a lawsuit that resulted in the revocation of all Steller sea lion research permits, and new permits do not allow capture of adult females. FY08 work will continue to develop and evaluate the safety of sea lion capture techniques, as well as continue analyses of foraging behavior and physiology. Successful completion of this work will provide data which will be used to evaluate sea lion protection measures.
Issues & Justification
Measuring Steller sea lion foraging behavior and defining foraging habitat are essential components of studies that evaluate hypotheses for population declines or differential population recovery rates among areas, and to evaluate the efficacy of critical habitat and other management strategies to enhance recovery. Studies conducted during 2000-2005 primarily focused on quantifying the foraging behavior and health status of juvenile (up to 3 years old) because of concerns over potential effects of fisheries on prey available to juveniles within their foraging areas. Although that program was very successful in capturing and tracking this age class of sea lions, there are difficulties in capturing older animals and thus our understanding of sea lion foraging behavior is far from complete. In particular, foraging behavior and habitats of adult females is inadequately described to understand how nutritional needs are met during winter periods when many females are simultaneously nursing a pup and gestating a fetus. In addition to needing an improved understanding of sea lion foraging ecology to test hypotheses concerning population control mechanisms (top down vs. bottom up factors), fisheries managers require substantially better information upon which to judge the efficacy of fisheries management regulations required under the Endangered Species Act. In association with captures for instrument deployment, measurements and samples are collected from sea lions to evaluate their health and condition. These combinations of data and improved models to describe at-sea behavior in relation to environmental features will facilitate evaluation of potential indirect fisheries effects through prey species removals at increasingly finer scales of temporal and spatial resolution.
Goals
- Improve telemetry coverage to include more age and size classes, and data poor areas.
- Conduct modeling analyses with novel telemetry data filtering algorithms or path-analysis models to determine appropriateness of models for quantifying habitat use of foraging sea lions.
- Improve understanding of relationship between foraging behavior (combining tracking and diving data) and locations and environmental features that may reflect prey distribution.
- Combine foraging pattern data derived from satellite telemetry with haul-out distribution and abundance data to derive an estimated distribution for the population as a whole.
Methods
Capturing larger sea lions to improve understanding of sea lion foraging behavior will require refinement and evaluation of techniques for safe capture and handling of adults and larger juveniles. Field studies may utilize the opportunistic capture of sea lions in floating pens or the modification of an at-sea net capture technique that was developed and used successfully to capture adult Australian sea lions by other researchers. In addition to being instrumented, captured sea lions will have blood and other tissue samples collected, and morphometric measurements taken to assess health and condition status. Modeling analyses will also be conducted to better predict likely at-sea behavior based on telemetry data, examine habitat use by combining telemetry and environmental data, and evaluate the risk of capture and handling techniques on short-term survival.