We conducted a modified catch-survey analysis incorporating commercial catch per unit effort and bottom-trawl survey data for the blue king crab stock, Paralithodes platypus, near St. Matthew Island in the eastern Bering Sea. Although the general area was surveyed to estimate abundance of crabs, the commercial fleet fished over a more limited and generally untrawlable portion of the surveyed area. Therefore, the current abundance estimation procedure based on assessment surveys was modified to include fishery performance data to explore the utility of both types of data in estimating abundance. Total annual catch and observed relative survey abundance of legal-sized crabs were classified into recruits and postrecruits by shell age and size, and commercial fishing effort was defined as total potlifts. The analysis separated measurement errors from the true changes in population abundance and converted the relative abundance to an absolute value. The analysis also provided smoothed annual estimates of the legal blue king crab abundance. Based on a probable range of instantaneous natural mortality(0.16 to 0.35) and fishing effort weighting factors (0.5 and 1.0), we estimated survey catchability to be 0.91 to 1.25. Weighting the fishing effort heavier or assuming higher natural mortality resulted in lower estimates of survey catchability. Because of confounded effects among survey catchability and natural mortality, additional information is needed to reliably estimate these parameters.
