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<br />. <br /> <br />. <br /> <br />Although a 2-4 day BHBF may briefly create additional pool area at the mouth of the <br />LCR, that effect is unlikely to substantially benefit drifting HBC, which would <br />subsequently be flushed into the mainstream. Flows of 45,000 overtop existing bars in <br />the LCR area, and expose shoreline and backwater habitats to cold temperatures and <br />high velocity flows. Thus, high flows stress and displace young HBC in those habitats. <br />Therefore, even brief BHBFs from May through July may negatively affect HBC <br />recruitment throughout the mainstream. <br /> <br />The Reasonable and Prudent alternatives of the 1994 B.O. include BHBFs, however, <br />the Service determined some HBC may be taken during high flow events. The <br />discussion of incidental take considered testing and studies to determine impacts of <br />flows on young humpback. One goal of a BHBF is the redistribution of channel-stored <br />sediment to rejuvenate margin and current return channel nursery habitats for young life <br />stages of HBC along the mainstream. This hypothesis will continue to be tested <br />through the proposed 1998 BHBF(s). <br /> <br />The 1996 B.O. indicated that little impact on mature HBC was anticipated, and this <br />conclusion was supported by data collected in association with that event (Valdez <br />1997). The 1996 BHBF did not serve as a spawning cue for movement into the mouth <br />of the Little Colorado River. High flows did result in substantial additional drift, and <br />radio-tagged HBC shifted location to the low velocity portions of eddies. Although some <br />scour of the benthos occurred, rejuvenation of return current channels and other <br />mainstream backwater habitats was brief and persisted only for about 6 months. <br />Therefore, there was little additional recruitment habitat for young HBC by the late <br />summer in 1996. In conclusion, the 1996 BHBF had little effect on HBC, and <br />apparently did not adversely affect them. <br /> <br />The Service's B.O. on Reclamation's 1997 HMF expressed concern regarding the high <br />levels of winter mortality sustained by Grand Canyon HBC. That B.O. permitted <br />Reclamation to proceed with the flow event, but stipulated that Reclamation initiate a <br />study of the causes of HBC winter mortality, and support the recovery process. <br />Working through the GCMRC, the study of overwinter mortality of HBC has been <br />included as part of the FY 99 GCMRC Research and Monitoring Plan. <br /> <br />Conclusions <br /> <br />A BHBF is not likely to adversely affect subadult or adult HBC between May and July, <br />because those age classes of HBC appear to be well-adapted to high flow events. <br />However, the timing of high flow events may affect larval and young HBC, depending <br />on the spawning peak in 1998. BHBFs from May through July, during the spawning <br />and drift phase of the HBC life history cycle, in the LCR, may negatively affect the HBC <br />population, by reducing annual survivorship and recruitment in the mainstream, and <br />may flush refugial backwater habitats along the mainstream. <br /> <br />The period 1995 through 1997 appeared to be rather normal recruitment years (Tuegel <br /> <br />1998 GCD Beach/Habitat Building Flow 15 <br /> <br />Biological Assessment <br />