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<br />003156 <br /> <br />,. <br /> <br />METHODS <br /> <br />Several important insights into the interrelationships between stream- <br />flow, trout habitat (by life stage), and trout population dynamics came out <br />of the IFIM/PHABSIM studies. In most instances, the limiting life stage for <br />both rainbow and brown trout was the fry. In a few instances, the spawning/ <br />incubation habitat was limiting. There were no instances where the data <br />analysis indicated the weighted usable area (WUA) habitat values for the <br />juvenile and adult life stages were limiting. <br /> <br />In light of the above general findings, minimum and optimum flow <br />recommendations on a critical and seasonal period basis will be made for <br />each of the study streams by life stage and species as follows: <br /> <br />l. Spawning/incubation/hatching <br />2. Two- to four-week-old fry <br />3. Juvenile <br />4. Adult <br /> <br />The flow recommendations for spawning, incubation, and hatching will be <br />made as one minimum recommendation. Flows should not be allowed to fall (if <br />at all possible) below the spawning level at any time during those three' <br />life stages. Reiser and White. (198l, 1983); Becker, Neitzel, and Fickeisen <br />(l982); Becker, Neitzel, and Abernethy (l983); and Neitzel and Becker (l985) <br />made several salient points in evaluating the impacts of redd dewatering on <br />salmonid reproductive success. Among other things, they found that redd <br />dewatering for upto8 hours or more for several days to weeks did not have <br />a detrimental impact on egg and embryo survival as long as: l) intra-gravel <br />humidity levels were maintained at lOO% saturation; and 2) maximum and <br />minimum intra-gravel temperature extremes did not reach the lethal limit. <br />These findings, however, applied only to the pre-hatching developmental <br />period. Once hatchi~g occurred, removal of intra-gravel water flows for <br />even l-3 hours resulted in heavy mortality for sac fry and intra-gravel <br />dwelling .alevins. . Thus,. to minimize the negative impacts of flow reductions <br />due to either thermal shock and/or loss of intra-gravel flows during the <br />post-hatching intra-gravel life stage, one minimum flow recommendation will <br />be made. Fry, juvenile, and adult life stage flow recommendations will be <br />made for both minimum and optimum conditions. <br /> <br />Trout population data and USGS gaging record information were used <br />together with the IFIM/PHABSIM data to formulate the minimum and optimum <br />flow recommendations. Post-emergent fry collections have been made on all <br />of the study streams to define the critical fry emergence period (Table l). <br />Spawning, incubation, and hatching periods were defined from field <br />observations and general biological information and life history <br />characteristics. <br /> <br />The flow recommendations made in this report are meant to be realistic <br />guidelines for protecting minimum and optimum flow and habitat requirements <br />for the rainbow and/or brown trout populations within the stream study <br />sections as defined in Table 2. The recommendations are not meant to be <br />rigid limits that must be steadfastly adhered to. Rather, they are guide- <br />lines that should adequately protect the wild trout populations found in the <br />study streams to a reasonable degree. The minimum flow recommendation for <br /> <br />C. .~. -,. <br />:....,. . <br />,j.! '~". <br /> <br />~, . <br /> <br />S liQ002383 <br />