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8 Task 3: This was an extension of spring backwater sampling in (1) above, and served to expand upon prey vulnerability/selectivity in fish species in close spatial association with northern pike and channel catfish in these habitats. Stomach content data on channel catfish was limited due to limited captures and recent focus in Yampa above Craig. In 1991, sampling again focused on reaches inhabited by Colorado squawfish. Body width and depth measurements were taken from potential prey species including 107 f1annelmouth sucker, 79 roundtai1 chub, 61 Colorado squawfish, 46 carp, 46 white sucker, and 17 b1uehead sucker. Gape width and depth measurements were taken from predator species including 125 northern pike, 33 channel catfish, and 6 sma11mouth bass. Predator stomach contents were collected from 72 northern pik~, 31 channel catfish, 6 sma11mouth bass, and 2 Colorado squawfish. The squawfish stomach samples were gained as regurgitated prey from live fish. Processing of these data and samples is continuing. This completed the required field data collections. Sample and data processing was continuing through the fall of 1991 and winter of 1992, when the principal investigator was temporarily reassigned as acting program administrator for the statewide native aquatic wildlife program. Research activities were suspended until the position is permanently filled. Processing and analysis will be resumed at that time and final reporting for this project, including Jobs 1-3, will be accomplished in 1993. Job 6. Title: Standardized monitoring surveys Activities included in this segment are the 1991 and 1992 spring electrofishing for Colorado squawfish adults and fall seining for Colorado squawfish young-of-the-year. Fall Seining In 1991, 40 seine samples were collected, sampling 1,940 m2 of area in 20 backwater habitats in Reach 6 of the Colorado River. Seventeen fish species were captured, but species composition was dominated by three nonnative species: red shiner, fathead minnow, and sand shiner. Only one Colorado squawfish was collected. Similar to the past five years, the relative abundance of red shiner, fathead minnow, and sand shiner in 1991 comprised over 97% of the fish sampled (Fig. 2). Gamefish species, which are also nonnative species, included green sunfish, largemouth bass, channel catfish, and black bullhead and collectively comprised only 0.7% of the total sample. Native fishes, including bluehead sucker, Gila spp., flanne1mouth sucker, speckled dace, and Colorado squawfish, comprised only 1% of the total sample. Other nonnative species included Gambusia, carp, and white sucker. Trends in abundance of these groups of fishes demonstrate abundance of native fish young remain at very low levels since declining from over 25% of the species relative abundance in 1986. Abundance of introduced gamefish species, which may act as predators on native fish young, have remained at insignificant abundance levels since 1986. Red shiner and fathead minnow numbers appear to fluctuate inversely since 1988, with one or the other species dominating relative abundance in the seine samples. If introduced species are exerting a negative effect on native fish young in backwater nursery habitat, red shiner, fathead minnow, and sand shiner are more likely the responsible species. ,