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Background <br /> <br />1 <br />V_J1 <br /> <br />1 <br /> <br />INTRODUCTION <br />Floodplain corridors bordering the main-stem rivers in the Upper Colorado River <br />Basin are considered an integral and necessary element for the recovery of the four <br />endangered big river fish species (Colorado pikeminnow, Ptychocheilus lucius; <br />humpback chub, Gila cypha; bonytail, Gila alegans; and razorback sucker, Xyrauchen <br />texanus). Negative interactions between certain nonnative fish species and the young <br />life stages of endangered fishes in floodplain nursery habitats are a primary concern. <br />Lentic habitats including backwaters, embayments created by flooded terraces, and <br />ponds created in depressions have all been identified as critical habitat components <br />generally important to the native fish community and ecological functions supporting the <br />endangered fishes (Irving and Burdick 1995). However, 40 nonnative fish species are <br />present throughout the Upper Basin (Nesler 2003) and may adversely impact recovery <br />of endangered fishes through predation and/or competition at critical life stages and/or <br />in critical locales (Tyus and Saunders 2000, Mueller and Marsh 2002). <br />Nonnative fish known to occur in floodplain ponds, such as largemouth bass and <br /> <br /> <br /> <br />green sunfish, typically seek backwater or slow moving side channel habitats upon <br />entering the main stem river. Within these riverine habitats, centrarchids are believed to <br />pose a significant predatory threat to the young life stages of endangered and other <br />native fishes (Tyus and Saunders 1996, Osmundson 2003). <br />Study Goal, Objectives, and Approach <br />Goal -- To reduce proliferation of nonnative fish species in floodplain habitats <br /> <br /> <br />t <br />and minimize chronic escapement of nonnative fishes from perennial ponds. <br />Objectives -- Objectives identified during the course of this study included the <br />following: 1) assessment of ponds as problematic/non-problematic through inventory <br />and sampling efforts. Problematic ponds were those that contained nonnative fish that <br />had direct access to critical riverine habitat; 2) removal of nonnative fish via chemical <br />reclamation, water management, and/or black plastic installation; 3) installation of <br />screens to minimize reinvasion of ponds, escapement of fishes from treated ponds and <br />