These data represent density per square meter calculated from counts of fin fish made by divers on fixed transects on permanent subtidal monitoring sites around San Nicolas Island between 1981 and 2019. Fish were counted on seven sites, each of which had five midwater and five benthic fish transects. Six of the sites were first sampled in 1980, one additional was added in 1987. The sites have usually been monitored twice per year, most often in October and April. The midwater and bottom portions of each transect were sampled separately. Midwater transects were 50 m long by 5 m wide and encompassed the entire water column except the bottom 2 m (250 square meters). Bottom transects were 50 m long by 2 m wide and included only the bottom 2 m of the water column (100 square meters). The list of species counted was expanded over time as new species were encountered and the data here include all 66 species counted.