Research Technical Report

Habitat Associations of Upper Slope Rockfishes (Sebastes spp.) and Co-occurring Demersal Fishes in the Headward Part of Ascencion Canyon, CA

Bizzarro, J.J., J.M. Field, H.G. Greene, R.N. Lea, and J. de Marignac (March 2003)

Poster presentation at the Sanctuary Currents Symposium, Seaside, CA

ABSTRACT

Due to their typical life history patterns (slow growth, late age at maturity, and extreme longevity) deep-water rockfishes (Sebastes spp.) are especially susceptible to overfishing, as evidenced by recent declines in most commercially targeted stocks. To establish effective Marine Protected Areas (MPAs), the interaction between fishes and their available habitats must be determined. Our objectives were to describe habitat associations for rockfishes and co-occurring fish species within the headward part of Ascension Canyon at large (100s of meters to kilometers) and small (10s of meters) scales. Geologic structure and lithology were investigated using high-resolution multibeam bathymetric and backscatter data. These data were interpreted to produce habitat maps of the study area. Seafloor features and fish assemblages were then surveyed using the Delta submersible along 50-meter depth contours, between 200 and 350 meters. Thirty-two ten minute transects were completed between two distinct large-scale habitat types. At 200 and 250 m, stripetail (Sebastes saxicola) and greenstripe (S. elongatus) rockfishes were the dominant fish species. At 300 and 350 m, splitnose (S. diploproa) and shortspine thornyhead (Sebastolobus alascanus) were the most abundant rockfishes. Large and small-scale habitat associations of these and several other commercially important demersal fishes were also determined.