SUSTAINABILITY OF FLATFISH-DOMINATED FISH ASSEMBLAGES IN HECATE STRAIT, BRITISH-COLUMBIA, CANADA

Species catch-rate data from a series of four trawl surveys of the Hecate Strait region in British Columbia, on the Pacific continental shelf of Canada were analysed using agglomerative clustering techniques. Four relatively stable fish assemblages were identified. These assemblages were dominated by flatfish species and characterized by depth and bottom type. Although the relative abundances of component species within assemblages did change seasonally, we observed little change in terms of which species were dominant. Geographical boundaries of the assemblages were also relatively stable over the four surveys completed to date. Persistent boundaries were found in the 50-60 m range and 130-140 m range. We identified both regular and seasonal components of assemblages. Arrowtooth flounder and Pacific sanddab showed remarkable stability in their overall distributions, leading us to suspect that survey catch rates for these species would be suitable for monitoring changes in abundance. We found no significant differences in either component abundance or diversity of assemblages under two widely different fishing effort regimes in different portions of the Strait.