Laserfiche WebLink
<br />VI. Study Methods/Approach <br /> <br />) <br /> <br />A two-year biological study is planned following construction of fish <br />passage at GVIC Diversion Dam to evaluate if fish will move upstream <br />through the passage structure. Field efforts for this evaluation will <br />rely on two separate techniques. both applied independently to <br />determine if sub-adult and adult fish will use the passageway to pass <br />over the GVIC Diversion Dam (river mile 185.1). The first method will <br />involve mark and recapture efforts in the immediate vicinity of the <br />diversion dam using electrofishing. Sub-adults and adults of the most <br />common large-sized. native fishes, flannelmouth sucker, bluehead <br />sucker, and roundtail chub, will be captured and PIT tagged. Plans are <br />to PIT tag approximately 1.000 fish from these three species. Attempts <br />will be made to PIT tag the number of flannelmouth. bluehead, and <br />roundtail to closely approximate the relative percentage that each <br />species comprises the population in the IS-mile reach of the Upper <br />Colorado River. Other common sub-adult and adult nonnative fishes such <br />as common carp and white sucker that are captured will be marked with <br />external, individually numbered Floy tags. <br /> <br />) <br /> <br />Other nonnative fishes such as centrarchids (largemouth bass. green <br />sunfish. etc.), ictalurids (channel catfish. black bullhead), and <br />esocids (northern pike) that are captured as "by-catch" will be removed <br />and disposed. The reason for removing these introduced fish is that <br />they are suspected of adversely affecting the native mainstem fishes of <br />the Colorado River basin in some fashion. Warmwater gamefish. such as <br />centrarchids. ictalurids. and esocids. are listed as frequent <br />contributors to the decline of native fishes and are thought to have <br />the greatest adverse effect on endangered native fishes. An increasing <br />body of evidence characterizes the negative interactions of nonnative <br />fishes with the endangered big river fishes (Hawkins and Nesler 1991; <br />Minckley et al. 1991; Maddux et al. 1993; Lentsch et al. 1996). Some <br />of this evidence is indirect that includes inferences from field data <br />or results from laboratory studies of predation by nonnatives on <br />natives. Laboratory studies have documented agonistic behavior. <br />resource sharing. and vulnerability to predation (Papoulias and <br />Minckley 1990; Karp and Tyus 1990; Ruppert et al. 1993; Johnson et al. <br />1993). Direct evidence or predation includes native fishes obtained <br />from stomach contents of nonnative fishes and by visual observation of <br />predation. The loss of early-life history stages of the razorback <br />sucker has been linked to predation by nonnative fishes. While it is <br />not likely that nonnative fishes that have become established in the <br />Upper Colorado River Basin can be eliminated. preventive measures and <br />active control programs could be implemented to reduce the abundance of <br />nonnative fishes in riverine and adjacent floodplain habitats. <br /> <br />GVIC 5 <br />