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,. . , ~ c) /-- ~ CD ~fI: ;I ~ ~ . ~ ;) ~ ~ .. ~ ~ ..J 1.1 ~ !d. -i .. .., .tI ;;.. $1 <d .'If .1/1 I .. ,.j . .,; ~ ~ ,fj .... .<f ;.J ~. ~ ... <Ii ~ CJ 12.9 river miles (S.E.=1.5, N=182) for channel catfish and 5.5 river miles (S.E.=O.S, N=281) for common carp. Radio telemetry studies of IS channel catfish implanted with 40-MHZ tags and equipped with external antennae (400-day tags for fish >550 mm TL, 130-day tags for fish 350-365 mm TL) confirmed the lack of long distance seasonal migrations observed during mark and recapture studies. Adult channel catfish occupied primarily run habitats throughout the year, but during winter base flows a greater number of habitats were selected with eddies, slackwaters, and pools occupied primarily. During high spring flows in June, two of eight individuals still containing transmitters (all others expelled at that time) moved into side channel runs where current velocities were lower than those measured in main channel runs. Movement (egression/ingression) of native and non-native species between main and secondary channel habitats was studied during 1994-1995. Fish movement at the up- and downstream mouths of secondary channels were sampled by hoop net to measure direction (in,out) and timing of fish movement under varying flow conditions. A total of 841 native and 21,906 non-native fishes were collected in 1994. In 1995, 2,S36 native and 6,559 non-native fishes were sampled. Roundtail chub Gila robusta was the only rare native species recorded. Speckled dace Rhinichthys osculus was the most common native species sampled and non-native samples were primarily red shiner Cyprinella lutrensis and fathead minnow Pimephales promelas. During July 1994 sampling at high flows, more than 90% of the total specimens were collected. Collections during high August 1995 flows yielded the greatest number of specimens for the year, including 91 % of all native specimens. Other than increased movement of native species during high flow conditions, there were no statistically significant differences. To evaluate piscivory by non-natives on native fishes and commonality of food resource use between the two, we analyzed food habits of San Juan River fishes, 1991-1995. Due to the channel catfish's abundance and widespread distribution, analysis of its food habits was emphasized during 1991-1993. During 1993-1995, we analyzed the food habits of both native and non-native species in association with egression/ingression sampling. All potential large- bodied non-native piscivorous fishes (primarily striped bass, walleye, largemouth bass Microplerus salmoides) were sacrificed and stomach contents examined in the field for presence/absence and identification of fishes consumed. Macroinvertebrates were sampled during 1993-1995 to assess abundance and availability of foods for native and non-native fishes. Piscivory in channel catfish was documented in 13.2% of312 specimens, primarily in catfish >450 mm TL. All stomachs of other non-native piscivores containing food items yielded fish and/or fish remains. We did not document piscivory on rare fishes, and flannelmouth sucker Catostomus latipinnis was the most common native species consumed. Examination of stomach contents of small-bodied native and non-native species and young-of-year and juvenile life stages oflarge-bodied native and non-native species indicated considerable overlap of macroinvertebrate orders consumed. The macroinvertebrate community, when compared to other Colorado River Basin streams, was lower in abundance and diversity (lowest taxonomic level identified was Family). The reduced and abundance of the San Juan River macro invertebrate community is likely due to the higher frequency and magnitude of late San Juan River Non-native Species Interactions, Final Report, I February 2000 111