These data represent counts of fin fish made by divers on fixed transects on permanent subtidal monitoring sites around San Nicolas Island between 1981 and 2019. Beginning in 2014, total length was estimated for most individual fish or size ranges were estimated for fish in schools. 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 5 m wide and encompassed the entire water column except the bottom 2 m. Bottom transects were 2 m wide and included only the bottom 2 m of the water column. The list of species counted was expanded over time as new species were encountered and the data here include all 66 species counted.