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<br />fish is enhanced in the main channel because larger fish are less susceptible to predation by <br />nonnative fish. These potential benefits could be offset, however, if nonnative fish species also <br />experience enhanced growth and survivorship. In fact, some native species may gain advantage <br />because they are adapted to the lentic environment of the floodplain wetland. Therefore, <br />management and maintenance oflhese wetlands require considerable understanding of the <br />community ecology of native and nonnative species and their interactions. <br /> <br />Additionally, enhanced productivity of floodplain wetlands may be important in enhancing <br />survivorship of adult native fish. Modde (pers. eomm.), Osmundson and Kaeding (1989), Tyus <br />and Karp (1990, 1991), and Holden and Crist ( ) documented the use of floodplain wetlands or <br />low velocity areas by adult razorback sucker. Wick (pers. comrn.) speculated that adult fish use <br />highly productive areas to replace valuable energy reserves exhausted while spawning. Resting <br />habitats, therefore, may be important to enhance the survivorship of the adult population of <br />razorback suckers in the Upper Basin. <br /> <br />Levee Removal Issues <br /> <br />The following paragraphs lists primary issues concerning the floodplain habitat enhancement <br />component ofUCRBRIP. We have listed each issue either as a statement or a question. Each <br />issue is followed by a brief discussion. The discussion of each issue is in the levee removal <br />strategy. <br /> <br />Naturally Flooding Wetlands will be Used to Develop Mailagement Criteria. To date, most of <br />the effort on the benefits of floodplain function to endangered species within UBRIP focused on <br />"manipulated" sites that use human intervention to control flooding. A substantial amount of area <br />floods naturally in the Colorado River system; yet little, if any attention, has been given to <br />naturally flooding wetlands in the basin even though substantial flooding occurs in some areas <br />during high flow years (e.g. 1983, 1984, 1995; Crowl, pers. obs.). This strategy, combined with <br />information from previous studies, allows managers to detennine fish production dynamics in a <br />range of natural floodplain wetlands and specific restorations (levee removal) sites as they become <br />available. This document outlines a temporal and spatial strategy to compare fish population <br />response and dynamics of , restored' areas to that of natural floodplain areas. This plan contains a <br />monitoring protocol designed to detennine fish food (zooplankton, macro invertebrate, etc) and <br />fish population responses (both native and nonnative) associated with these wetlands. <br /> <br />Role of Manipulated Sites. Manipulated sites (i.e. Old Charlie, Walter/Walker, Johnson, Boat <br />Bottom, etc.) will be used to address specific questions concerning floodplain function. Sites with <br />control structures provide an opportunity to answer questions that cannot be addressed in existing <br />natural wetlands, particularly as they relate to timing and duration of inundation. In addition, they <br />offer an opportunity to use control structures to increase effectiveness of fish sampling. Site <br />manipulation is integrated with the levee removal strategy to address specific hypotheses <br />regarding floodplain and wetland ecology. This approach will be gradually implemented in each <br /> <br />5 <br />