Variability in trawl survey catches of pacific ocean perch, shortraker rockfish, and rougheye rockfish in the Gulf of Alaska

Little information is available on the comparative variability of Pacific ocean perch, shortraker rockfish, and rougheye rockfish catches in Alaska trawl surveys. In this study, data were first examined for these three species from three localized experimental bottom trawl surveys in the Gulf of Alaska in 1993, 1998, and 1999 to compare the variability of catch rates for each species. When catch rates were analyzed within favorable fishing areas for each species, the coefficients of variation for Pacific ocean perch were approximately 2.5 to 3 times greater than those of shortraker or rougheye rockfish, indicating that the latter two species are much more even in their distribution. To provide a broader comparison of variability, catch rates of the three species were also examined from seven large-scale bottom trawl surveys conducted in the Gulf of Alaska from 1984 to 2001. Using geographic information systems software, subsets of the hauls in these surveys were selected in what were determined to be favorable fishing areas for either Pacific ocean perch or for shortraker and rougheye rockfish. Analysis of the species' catch rates in these hauls indicated results that were very similar to those of the experimental trawl surveys; the variability of Pacific ocean perch was 2.1-2.3 times greater than that for either shortraker or rougheye rockfish. The results of this study indicate that a trawl survey for shortraker and rougheye rockfish based on a random design may be logistically feasible, but that an alternative design would be needed for Pacific ocean perch in order to be cost effective.