AFSC/ABL: Rockfish Habitat Dive Video Transects

Many species of commercially valuable rockfish (Sebastes spp.) inhabit waters on the outer continental shelf in the Gulf of Alaska typically between depths of 100-300m. The benthic habitat requirements and spatial distribution of these rockfish species is relatively unknown. Information regarding benthic habitat use would improve current stock assessments and provide baseline information for an ecosystem approach to management. Several study areas in the Gulf of Alaska have recently been mapped with high resolution multibeam bathymetry and backscatter to generate detailed benthic habitat maps. Large populations of rockfish have been surveyed and harvested within these mapped areas. The NMFS MESA group conducted two submersible observation surveys in summer 2005 on three of these mapped areas, Albatross Bank, Hazy Islands, and Cape Ommaney. The objectives of these surveys were to collect information on rockfish habitat interactions and generate density estimates by habitat. Forty dive transects were completed on the mapped sites using the Delta two-person occupied submersible. We identified numerous gravid females and observed schooling behavior of several species over particular benthic habitats. Density estimates of rockfish using strip and line of sight methodologies are being determined by substrate and invertebrate habitat classification. We identify habitat types with high densities of rockfish species and describe differences between estimation methods.