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11 reproductive activities of Colorado squawfish. They further stated that alteration of this hydrological event may affect initiation of Colorado squawfish migration and spawning. Additionally, maintenance of low stable flows in summer and fall are necessary for growth and survival of young Colorado squawfish. Migration of the Colorado squawfish is cued to the ascending limb and natural spawning is initiated on the descending limb of the annual hydrograph as water temperatures approach 200 C (Tyus and Karp 1989). Spawning, both in the hatchery and in the field, generally occurs in a 2-month timeframe between July 1 and September 1. although high-flow water years may suppress river temperatures and extend spawning in the natural system into September. Temperature also has an effect on egg development and hatching. In the laboratory, egg mortality was 100 percent in a controlled test at 130 C, At 160 to 180 C, development of the egg is slightly retarded, but hatching success and survival of larvae was higher. At 200 to 260 C. development and survival through the larval stage was up to 59 percent (Hamman 1981). Juvenile temperature tests showed that preferred temperatures ranged from 21.90 to 27,60 C. The most preferred temperature for juveniles and adults was estimated to be 24.60 C. Temperatures near 240 C also are needed for optimal development and growth of young (Miller et al. 1982). (:' ':~: .';~ Ir ;>, Limited temperature data exist for the San Juan River; however, water temperatures in occupied habitats (as measured at Shiprock and Bluff) currently are well within an acceptable range to expect successful spawning. egg development. and hatching. assuming other habitat/flow conditions are available to the fish. , i While consistent temperature data for pre- and post-Navajo Dam conditions do not exist. some important changes can be noted by a review of available data. Olson (1962a), during his preimpoundment study, recorded temperatures as high as 250 C during July and August 1961 near Rosa, New Mexico. on the San Juan River. A short distance downstream near Bl~nco, New Mexico. Olson measured temperatures in excess of 260 C during the same time period. (Tables 1. 2. and 3. Appendix C) Recent temperature readings document a significant change since the closure of the Navajo Dam. In July 1989, the New Mexico Department of Game and Fish measured 130 C on the San Juan River at the Highway 64 bridge crossing, just upstream of Blanco. New Mexico. Cold-water releases from the Navajo Dam and their effect on water temperature in the San Juan River can be seen as far downstream as Farmington, New Mexico. and the confluence with the Animas River. Downstream of Farmington, ambient air temperature and. to a lesser extent. the warmer water from the Animas River tend to ameliorate the effect of cold-water releases from the Navajo Dam throughout currently occupied Colorado squawfish habitat. Post-Navajo water temperatures on the San Juan River at Farmington, New Mexico, and particularly at Bluff, Utah, are still warmer for a longer period of time than anywhere else in the Upper Basin. (Tables 4 and 5, Appendix C) " ". ~';:,'; , k ~. ~<.~ '", .c;,