A comparison of length distributions of rockfishes (Sebastes spp.) from submersible and trawl surveys off central California

Data from the West Coast Bottom Trawl Survey and from surveys conducted with a manned submersible in nearby untrawlable areas were used to compare length distributions for greenspotted rockfish (Sebastes chlorostietus), greenstriped rockfish (S. elongatus), canary rockfish (S. pinniger), and vermilion rockfish (S. miniatus) off central California. For all 4 species, broader size ranges and greater proportions of small fish were present in the data from the submersible surveys, and length distributions were significantly different (P<0.01) in comparisons of all lengths from the submersible surveys with all lengths from the trawl surveys, as well as in comparisons of lengths from the submersible surveys and trawl surveys over trawlable habitat. For 3 species, length distributions were significantly different in comparisons of lengths obtained from submersible surveys on trawlable and on untrawlable habitats. Trawl selectivity curves from recent stock assessments were evaluated in relation to the length data for greenspotted, greenstriped, and canary rockfish. Although derived from a larger spatiotemporal extent than our study, greenspotted and greenstriped rockfish selectivity curves appear to account for the reduced frequency of small fish in the trawl survey, whereas the canary rockfish selectivity curve does not. Similar comparisons between submersible and trawl-survey rockfish lengths from other regions of the west coast could help address spatial variability in trawl survey selectivity and further inform selectivity functions for stock assessments.