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<br />'. <br /> <br />Peter Evans, Director <br /> <br />2 <br /> <br />. <br />. <br /> <br />Fish and Wildlife Service biologists report that the combination of a high peak (29,900 cfs in the <br />IS-Mile Reach) in 1995, which stayed above 20,000 cfs until mid July, followed by a moderately <br />high peak in 1996 resulted in very successful Colorado pikeminnow reproduction in 1996. This <br />same pattern also occurred in the mid-1980's when two moderately high years (1985 and 1986) <br />fell on the heels of2 flood years (1983 and 1984) resulting in high reproduction and later strong <br />recruitment to the adult population (early 1990's). While it will take several years to confinn, it is <br />anticipated that 1996 will also become a strong year class. There has been a steady increase in <br />adult Colorado pikeminnow in the Colorado River between 1991 and 1998, particularly in the <br />upper reach, from Westwater Canyon to Palisade (see Figure. 2), including the IS-Mile Reach. <br />This has primarily resulted from recruitment of the strong year classes of the mid-1980's <br />mentioned above, but also from some year classes hatched in the early 1990's. <br /> <br />As the number of adults increases in the IS-Mile Reach, the importance of meeting the flow. <br />recommendations there becomes greater, i.e., when numbers are low, reproduction primarily <br />limits the ability of the population to increase; when numbers become high, the amount of suitable <br />habitat becomes limiting (carrying capacity may be reached). The flow recommendations were <br />designed to maximize the amount of optimum habitat for adults and thereby increase the carrying <br />capacity there. The flow augmentation from Ruedi and Wolford Mountain Reservoir was critical <br />in providing adequate habitat for the Colorado pikeminnow that inhabit the IS-Mile Reach and in <br />making room for additional adults this year. Flows in late summer 1998 would have dropped off <br />dramatically in mid-September to about 660 cfs without the augmentation of flows that we were <br />able to provide. <br /> <br />. <br /> <br />Responses of the fisQ community to flow augmentation are difficult if not impossible to quantify <br />on a short-term basis. As described above, the objective is to provide room for a growing <br />population of Colorado pike minnow, which we appear to now have, and in the future, for <br />razorback suckers if augmentation efforts prove successful. Annual reports for four studies <br />dealing with the IS-Mile Reach in 1998, including the population abundance survey described <br />above, are included for your review. <br /> <br />After preparing these reports for the past several years it has become apparent that the <br />requirements for reporting need to be revised to include a period of time necessary to detect a <br />biological response. The Service believes reporting back to the CWCB and Reclamation every 5 <br />years would provide a sufficient time period to identify changes in the IS-Mile Reach and in the <br />fish populations. Thus, we recommend that the next report be prepared in 2003. This would <br />capture a time period when more effort has gone into meeting Service flow recommendations for <br />the IS-Mile Reach starting in 1998 and would include the benefits offlow augmentation provide <br />by the Programmatic Biological Opinion for the Reach. This time period would also coincide well <br />with the biannual checkpoints identified in the Opinion. <br /> <br />The Service continues to believe that flow augmentation from these reservoirs has been an <br />important step in improving habitat conditions in not only the IS-Mile Reach but also the reaches <br />downstream. <br /> <br />. <br />