Food Partitioning among Fishes of the Virgin River

Food partitioning of one introduced and six native fishes was investigated from two different sites in the Virgin River. Replicate benthic samples from riffle areas indicated that chironomid and simuliid larvae composed the major food base available to fishes. Relativized electivity values suggest that chironomid larvae were nearly always selected over simuliid larvae by all species. Stomach analysis revealed seasonal interand intra-specific differences in diets. Desert and flannelmouth suckers fed on a mixture of sediment, detritus, filamentous algae and invertebrates. Roundtail chubs consumed largely Spirogyra, Cladophora and diatoms. Woundfin and spinedace were omnivorous, consuming an array of benthic and drift animals and plant matter. Speckled dace and red shiners were insectivorous, consuming large numbers of small dipterans. Food overlap among native fishes was uncommon, occurring in a biologically meaningful way on only four (7%) of the 55 possible occasions. Biologically meaningful food overlap (>0.60) between the exotic red shiner and native fishes occurred on four (25%) of the 16 possible occasions.