Project Description
Determination of prey consumed by marine mammals is an important component of studies to assess the health and condition of the population, investigate seasonal changes in deiet, and the overlap and competition with commercial fisheries. Examination of scat collected on land where Steller sea lions or Northern fur seals haul out is a source of reliable and consistent information on prey consumed. Scats are then examined in the laboratory and various prey body parts are examined and prey species identified. This information is used to describe the diet of animals from a specific site, compare among sites (rookery complexes and islands) and examine changes in diet that may reflect changes in availability of prey.
Issues & Justification
One of the greatest challenges facing Steller sea lion and northen fur seal researchers is the question of potential competition for prey between sea lions or fur seals and commercial fisheries. Scat analysis provides an opportunity to examine the prey diversity and size of prey consumed by sea lions hauling out on sampled areas. Prey hard parts (fish bones, cephalopod beaks) will be recovered and used to identify prey to the most specific taxonomic level. This information can provide a range of size age classes for prey consumed by season and location and that data can then be contrasted with existing information on fisheries catches. Seasonal and spatial changes in prey types may reflect changes in animal use areas and/or changes in the availability of prey in the Bering Sea and North Pacific. Intertwined with this work is ongoing research designed to produce keys of prey types and estimate prey size based on bones other than otoliths.
Goals
- Collect scat at designated Steller sea lion and northern fur seal rookeries and haulouts in Alaska
- Identify prey from collected scats
- Continue to develop regression to estimate fish length from bones rather than otoliths
- Determine northern fur seal diet among islands and among rookery complexes within islands
Methods
Northern fur seal and Steller Sea lion scat will be collected during brand-resighting cruises (sea lions) visiting known haul-outs and rookeries and during regularly scheduled capture trips and concomitant with fur seal abundance studies. Samples will be rinsed through a set of nested sieves to recover prey hard parts (fish bones, squid beaks). Fish otoliths, squid beaks, and distinguishable bones will be used to identify the prey to the lowest taxonomic level.