- Black Rockfish are important commercial and recreational species and understanding their biology is useful in developing best management practices. A common means to assess diet in both freshwater and marine fishes is stomach content analysis, which can determine diet composition and infer foraging behaviors. We conducted a stomach content analysis on 263 Black Rockfish stomachs from fish caught off Newport, Oregon in March and June through September. We enumerated and identified prey taxa to determine an index of relative importance (IRI) for prey groups. We processed stomachs and recorded prey weight, number of prey, and prey variation per stomach and measured total (filleted) length and sex for each sample. We found crab megalopa had the highest IRI but were not significantly more important than other prey groups. We did not find a significant difference in the diet habits of male and female fish; although, female fish had on average higher prey weight, number of prey, and variety of prey per stomach. Females have a higher reproductive investment which may account for this. We found there were significant differences between months, with prey weight per stomach increasing from March to September. In all three measures September had the highest mean weight, number, and variety of prey per stomach and March had the lowest. This indicates potential shifting of prey availability and abundance seasonally as well as potential changes in energy demands with reproductive efforts driving increased feeding rates.
Key Words: Black Rockfish, stomach content analysis, Index of Relative Importance, diet analysis