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( c <:) G ,~ ...' o ( <- tagged. Information from the recapture of pit-tagged fish in subsequent years will help to verify growth information, survival estimates, and to analyze fish movement. After the initial sampling, two additional electrofishing samples will be made to mark and recapture fish for population size estimation. During the first recapture collection, a tally of marked fish will be recorded and all unmarked fish will be marked (fin clip or similar) as on the previous sample. On the second. recapture collection, all fish will be counted with a separate tally of marked fish that are recaptured. The rationale for using a multiple mark-and- recapture population estimate is to allow for enough recaptures to provide suitable confidence intervals. Because of the relatively large size of the stream, it may be difficult to adequately estimate the population size using a single recapture collection. In addition to population studies, several fish will be radio tagged prior to the high-water releases. Their movements will be monitored throughout the period of the releases and holding locations will be characterized to determine habitat preference during high flows. Where practical, measurements will "be made of stream depth and width, substrata, flow, dissolved oxygen, nitrogen saturation, and temperature. As currently envisioned, the study will entail field work throughout the 7-year research period. Data obtained at different flows and changes in the fishery observed throughout the research period should provide a continuum to help determine suitable flows for the trout fishery. An annual report summarizing the findings of each year's field work will be submitted in December. Modifications made in the research protocol and recommendations for changes will be included in the annual report. The final report will be submitted within 12 months of the last field season. TAILWATERS INVESTIGATIONS-WATER QUALITY BaCkground: Changes in release patterns from reservoirs have been known to affect the quality of reservoir tailwaters. Releases in excess of 3,000 cts from Navajo Dam have been documented to cause nitrogen supersaturation for some distance downstream in the San Juan River. During the first testing of the turbines owned by the City of Farmington hydroelectric plant at Navajo Dam, a large volume of 'silt was discharged into the river. Recent studies at Abiquiu Dam on the Chama River in north central New Mexico have shown low dissolved oxygen concentrations. with high releases from the reservoir. Such changes in water quality are known to a~fect, often negatively, aquatic organisms, especially salmonids. u. S. Geological Survey water quality data are available for the San Juan River at Archuleta, New Mexico. Although these data cover nlJIllber of parameters, they are lacking for the purpose of determining short-term or temporary changes in water quality associated with changes in releases from the dam. Such changes could easily be missed in a single water sample taken only once a month. These short-term fluctuations may have a significant impact on the aquatic community. This ascertain changes associated with experimental releases for Colorado squawfish. The purpose of this study is to identify any changes in water quality that might be associated with the operation of the dam to mimic the natural hydrograph. Observed changes in the water quality mayor may not affect the tailwater fishery or the native fish community downstream. However, until changes are identified, it cannot be determined if they may be potentially detrimental to the aquatic biota . A21