Evaluating changes in spatial distribution of blue king crab near St. Matthew Island

The National Marine Fisheries Service (NMFS) performs trawl surveys in the Bering Sea each year on a 20-nautical-mile grid. Around St. Matthew Island increased tows are made to evaluate blue king crab stocks. The Alaska Department of Fish and Game (ADF&G) performed pot surveys near St. Matthew Island in 1995 and 1998, concentrating on more nearshore areas that cannot be sampled by the NMFS trawl survey. This research evaluated changes in spatial distribution of female and legal blue king crabs near St. Matthew Island from these two sources of data. Comparison of spatial distributions between the two methods was accomplished using geostatistic techniques, such as ordinary kriging. Analysis of pot and trawl surveys showed different trends in stock distribution and abundance between 1995 and 1998. The trawl survey appeared not to properly evaluate the nearshore component of the blue king crab stock, and the distance between trawl locations was too great to accurately measure spatial correlation. The NMFS trawl survey has been the only available source of data to estimate stock distribution and abundance of blue king crab in most years. The pot survey results presented here indicate that the trawl survey has not accounted for the extent of the blue king crab distribution which may lead to bias in using it to evaluate stock status.