Food habits of the dominant fishes collected from 1974 to 1980 at eight locations in Elkhorn Slough, California, and the adjacent ocean were investigated. Epifaunal crustacea was the major prey group identified from stomach contents of more than 2,000 fishes, followed by epifaunal and infaunal worms, and molluscs. Overall, 18 fish species consumed 263 different prey taxa, ranging from 10 taxa to 125 taxa per fish species and including 99 crustacean, 56 polychaete, and 39 molluscan taxa. Mean prey richness was greatest at stations near the ocean and lowest at inshore stations. Detailed dietary data for all prey taxa were summarized as trophic spectra for each fish species. Trophic spectra represented functional groups of prey and were used for comparisons of dietary similarity. Cluster analyses, based on trophic spectra, resulted in four feeding guilds of fishes. Of 18 fish species, seven (Amphistichus argenteus, Leptocottus armatus, Embiotoca jacksoni, Clevelandia ios, Gillichthys mirabilis, Cymatogaster aggregata, and Citharichthys stigmaeus) fed principally on epifaunal crustacea. Four species (Pleuronectes vetulus, Platichthys stellatus, Phanerodon furcatus, and Myliobatus californica) consumed mostly molluscs and infaunal worms. Two species (Psettichthys melanostictus and Triakis semifasciata) fed on mobile crustacea, and five species (Hyperprosopon anale, Engraulis mordax, Clupea pallasi, Atherinopsis californiensis, and Atherinops affinis) fed largely on zooplankton and plant material. Our results suggest that high food availability enhances the nursery function of inshore habitats, and emphasize the importance of invertebrate prey populations and the indirect linkage of plant production to the ichthyofaunal assemblage, particularly marine immigrant species that are likely 'estuarine dependent.'
