COMPARISON OF SUBMERSIBLE-SURVEY AND HYDROACOUSTIC-SURVEY ESTIMATES OF FISH DENSITY ON A ROCKY BANK

Submersible belt-transect surveys along a rocky bottom were combined w ith acoustic surveys of the mater column to estimate depth distributio n and density of fishes at Stonewall Bank, Oregon, in the northeastern Pacific Ocean from September through October 1991. The objectives of the study were to determine the proportion of fish in the water column that were not detected by submersible survey techniques and to compar e estimates of fish density near the bottom from submersible surveys w ith density estimates from hydroacoustic surveys. More than 75% of the fishes recorded on acoustic surveys resided in the bottom third of th e water column. Rock-fishes (family Scorpaenidae) were the predominate fish tars observed in the study area. Estimates of fish density from submersible surveys were more than six times greater than estimates of fish density near the bottom from hydroacoustic surveys. Submersible and acoustic surveys provided different, but complementary, informatio n regarding the use of rocky banks by fish. Submersible surveys provid ed estimates of fish density near the bottom and provided valuable gro und-truth for acoustic equipment. Hydroacoustic surveys provided estim ates of fish density in the portions of the water column not observed on submersible transects and provided additional information on the ve rtical and horizontal distribution of fishes. The combined use of subm ersible and acoustic sampling techniques provided a better understandi ng of how fish use rocky banks than did either technique alone.