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,. \ Ie I :e 00494 4 experimental work. Fiscal Years 2005-06, are specifically intended to be a milestone period in the experimental process in terms of assessing the knowledge gained through testing of these specific tlow and non-flow treatments (Mechanical Removal, BHBF's, revised implementation of the BHBF concept and less-constrained fluctuating flows intended to disadvantage non-native fish). During summer 2005, Knowledge Assessment workshops aim to identify remaining uncertainties related to the experimental treatments being tested in the Colorado River below the dam. This information provides the basis for identifying approaches and an experimental design that will hopefully be recommended for implementation as a second phase of experimentation, presumably starting with the FY 2007-08 combined work plan. Recommendation for Experimental Treatments in FY 2006 - Within its draft FY 2006 work plan, the GCMRC identifies two experimental treatments that are recommended for continued implementation during Water Year 2006 (starting in October 2005). These activities are also intended to provide continuity between the initial period of experimental efforts and the next phase that is approved and implemented. The first of these treatments, Mechanical Removal of non-native fish, was recommended as a four-year treatment in the GCMRC's 2002, experimental plan. The FY 2006 effort represents the fourth and final year of this reconuncnded experimental treatment. Although more costly than originally projected, the mechanical removal project has proven to be effective in reducing non-native salmonid populations in the Lower Marble Canyon and Eastern Grand Canyon reaches proximal to the confluence of the Little Colorado River. However, the implications of reducing the non-native trout population below Lees Ferry with respect to benefits to native fish recruitment are not yet known. The second recommended treatment (retum to MLFF during January through April, 2006) consists of field and modeling studies relating Experimental versus Modified Low- Fluctuating Flows to rainbow trout reproduction within the Lees Ferry and Upper Marble Canyon reaches. Results of experimental studies related to Experimental Fluctuating Flows (5,000 to 20,000 cfs daily range) during 2003-05, and related modeling simulations, suggest that the experimental flows were probably not a mechanism for increased rainbow trout mortality (with respect to either redds or fry) compared to normal MLFF operations, had they occurred during that time period. To verify or refute these simulation results, a return to normal MLFF operations during January through April 2006, is required to determine through field data, GCMRC FY2006 Annual Work Plan (Draft June 10,2005)