Fish assemblages around seven oil platforms in the Santa Barbara Channel area

In 1996 we surveyed the fishes living on and around seven off shore oil pla tforms in the Santa Barbara Channel area. We conducted belt transects at va rious depths in the midwater and around the bottoms of each platform using the research submersible Delta. The bottom depths of these platforms ranged from 49 to 224 m and the midwater beams ranged from 21 to 196 m. We found that there were several distinct differences in the fish assemblages living in the midwater and bottom habitats around all of the platforms. Both midw ater and bottom assemblages were dominated by rockfishes. Platform midwater s were dominated by young-of-the-year (YOY) or juveniles up to two years ol d. Rockfishes larger than about 18 cm total length were rarely seen in the midwater. The fish assemblages around the bottoms of the platforms were dom inated by larger individuals, primarily subadults or adults. Density of all fishes was similar between the bottoms and midwater of any given platform. However, the total biomass was much greater on the bottoms, owing to large r fish living there. There was a consistently greater number of species on the bottom than in the midwater of each platform, likely because of a large r variety of habitat types on the bottom. The fish assemblages also differe d among platforms. We found significantly higher densities of young-of-the- year rockfishes around platforms north of Pt. Conception compared with thos e in the Santa Barbara Channel, probably because the more northerly platfor ms are located in the more productive waters of the California Current.