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<br />) <br /> <br />)0 <br />, c' <br />".J ,,~ <br />;,:~:'j ~\ ~ <br />.') .- <br />.Ji-I~ <br /> <br />') <br /> <br />, <br /> <br />) <br /> <br />>'} <br /> <br />... <br /> <br />.~ '.~. <br /> <br />-' <br /> <br />" <br /> <br />12,9 river miles (S,E.=1.5, N=182) for channel catfish and 5.5 river miles (S.E.=0.8, N=281) for <br />common carp. Radio telemetry studies of 18 channel catfish implanted with 40-MHZ tags and <br />equipped with ex:temal antennae (400-day tags for fish >550 mm TL, 130-day tags for fish <br />350-365 mm TL) confirmed the lack oflong distance seasonal migrations observed during mark <br />and recapture studies. Adult channel catfish occupied primarily run habitats throughout the year. <br />but during winter base flows a greater nwnber of habitats were selected with eddies, slackwaters. <br />and pools occupied primarily. During high spring flows in June, two of eight individuals still <br />containing transmitters (all others ex:pelled at that time) moved into side channel runs where <br />current velocities were lower than those measured in main channel runs. <br /> <br />Movement (egression/ingression) of native and non-native species between main and secondary <br />channel habitats was studied during 1994-1995. Fish movement at the up- and downstream <br />mouths of secondary channels were sampled by hoop net to measure direction (in,out) and timing <br />of fish movement under varying flow conditions, A total of 841 native and 21,906 non-native <br />fishes were collected in 1994. In 1995,2,836 native and 6,559 non-native fishes were sampled. <br />Roundtail chub Gila robusta was the only rare native species recorded. Speckled dace <br />Rhinichthys osculus was the most common native species sampled and non-native samples were <br />primarily red shiner Cyprinella /utrensis and fathead minnow Pimephales promelas. During July <br />1994 sampling at high flows, more than 90% of the total specimens were collected. Collections <br />during high August 1995 flows yielded the greatest number of specimens for the year, including <br />91 % of all native specimens. Other than increased movement of native species during high flow <br />conditions, there were no statistically significant differences, <br /> <br />To evaluate piscivory by non-natives on native fishes and commonality of food resource use <br />between the two, we analyzed food habits of San Juan River fishes, 1991-1995. Due to the <br />channel catfish's abundance and widespread distribution, analysis of its food habits was <br />emphasized during 1991-1993. During 1993-1995, we analyzed the food habits of both native <br />and non-native species in association with egression/ingression sampling. All potential large- <br />bodied non-native piscivorous fishes (primarily striped bass, walleye, largemouth bass <br />Micropterus salmoides) were sacrificed and stomach contents examined in the field for <br />presence/absence and identification of fishes consumed. Macroinvertebrates were sampled <br />during 1993-1995 to assess abundance and availability of foods for native and non-native fishes. <br />Piscivory in channel catfish was documented in 13.2% of 312 specimens, primarily in catfish <br />>450 mm TL. All stomachs of other non-native piscivores containing food items yielded fish <br />and/or fish remains. We did not document piscivory on rare fishes, and flannelmouth sucker <br />Catostomus latipinnis was the most common native species consumed. Examination of stomach <br />contents of small-bodied native and non-native species and young-of-year and juvenile life stages <br />of large-bodied native and non-native species indicated considerable overlap of <br />macro invertebrate orders consumed. The macroinvertebrate community. when compared to <br />other Colorado River Basin streams, was lower in abundance and diversity (lowest taxonomic <br />level identified was Family), The reduced and abundance of the San Juan River <br />macroinvertebrate community is likely due to the higher frequency and magnitude of late <br /> <br />San Juan River Non-native Species Interactions, Final Report. 1 February 2000 <br /> <br />Jll <br />