| Abstract | We analyzed data from the National Marine Fisheries Service continental slope trawl surveys (1999-2002) to examine patterns in groundfish assemblage structure in relation to longitude, latitude, depth, temperature and inter-annual variation. The slope surveys spanned approximately 32-48 o N and 200-1200 m depth. We focused on the 26 most abundant species, which made up more than 95% of the catch by biomass. Assemblage structure was strongly correlated with depth and latitude. For the most part, change in assemblage structure appeared fairly continuous, although there were more abrupt changes at approximately 500-600 m and in the vicinity of Point Conception, Cape Mendocino and Cape Blanco. There was also an interaction between depth and latitude with more northerly sites having deeper scores on the canonical axes than more southerly sites of comparable depth. Shallower sites also showed more variation in assemblage structure with latitude than did deeper sites. We were able to identify five assemblages on the continental slope. Pacific grenadier, giant grenadier, deep sea sole, longspine thornyhead, and California slickhead formed a deepwater assemblage with a broad latitudinal range. Very shallow, southern species included splitnose rockfish, spotted ratfish, English sole, stripetail rockfish, chilipepper rockfish and shortbelly rockfish. Shallow, mid-latitude species included spiny dogfish, longnose skate, hake, rex sole, bigfin eelpout, and Bering skate. Darkbotched rockfish, arrowtooth flounder and Pacific Ocean perch were identified as a shallow, northerly assemblage. The final group, sablefish, brown cat shark, aurora rockfish, Dover sole and shortspine thornyhead, occurred at different depths over a range of latitudes, and might be best described as a shallow/mid-latitude and mid-depth/southern grouping. |