Pollock Conservation Cooperative Research Center
2001 Awarded Research Projects
Assessing the extent of competition between Steller sea lions and commercial fisheries
Alan Springer, Edward Gregr, Andrew Trites and Zohrab Mawani
Award: $56,000
Estimated completion: March 1, 2002
Abstract
We conducted a spatial and temporal analysis of fisheries data to assess the extent of overlap between groundfish fisheries and Steller sea lions in the Gulf of Alaska and Bering Sea. Such an analysis has never been undertaken before and has been noticeably absent from recent Biological Opinions addressing the effects of groundfish fisheries on Steller sea lions. Fisheries data (catch, effort and location) were combined with sea lion data (counts and foraging distances) to identify the potential degree of overlap in distributions (the joint probability of fisheries and sea lion probability). This analysis is needed to determine the effectiveness of fishery management measures intended to minimize impacts on Steller sea lions.
We began our analysis by averaging the number of sea lions counted by NMFS and other researchers at each haulout (n=123) or rookery (n=49) in Alaska from 1956 to 2000 to identify areas of high sea lion concentrations. Sea lion (and fisheries) data were split into two seasons: summer (June -August) and winter (October -April). Assuming that swimming sea lions were normally distributed around each rookery or haulout (i.e., sea lions have a higher probability of being near shore than being far out to sea), we calculated the probability of sea lions occurring within a 5km grid overlaid over the entire eastern Bering Sea and Gulf of Alaska. We parameterized this portion of the model using the mean distances traveled (and associated standard deviations) by satellite-tracked individuals reported by Merrick and Loughlin (1997).
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