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Evaluating the Efficacy of Trawl Exclusion Zones for Protecting Steller Sea Lion Groundfish Prey: Examining Local Fish Abundance and Movement Around Steller Sea Lion Rookeries

Groundfish stocks in Alaska are managed at large scales, however important ecological interactions, such as predation, spawning and habitat selection occur on local scales.  Furthermore, commercial fishing is an activity with potential for localized effects.  Improved understanding of the local abundance of fish is critical to understanding the potential for localized depletion by fishing.  In 1997, the western stock of the Steller sea lion population has been declared endangered.  One of the hypotheses for this decline was competition between the commercial groundfish fishery and Steller sea lions for prey.  In order to understand the effects of fishing on a local scale, we need to assess abundance and distribution of the prey fields in local areas.

This study assesses Steller sea lion prey distribution around rookeries and haulouts in the Aleutian Islands in the summer and winter.  A multi-year tagging study examined the movement and abundance of Atka mackerel relative to trawl exclusion zones.  In addition, catch per unit effort indices during a NMFS chartered research cruise were used to examine small scale patterns in prey composition of Steller sea lion prey, Pacific cod, rockfish and pollock.  Distribution patterns differed on a local scale in areas near Steller sea lion rookeries.  This study represents a multi- year multi- area effort to improve our understanding of interactions between sea lions, their prey, and the commercial fishery.