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C) C) ...... (.O ...... w 25 () ~ 20 ~ 0> Q) '0 , 0. 15 E ~ ~ Q) ~ 10 "" '(ii Cl :Ii 5 Q) ::< o 10/01 12/01 01/31 04/01 Date 06/01 08/01 10/01 - Shiprock 1951-1961 - Shiprock 1964-1986 - Projected Shiprock 1993-98 Figure 3.18. Seven-day running mean daily water temperature for the San Juan River at Shiprock, New Mexico, during pre-dam, post-dam, and research flow periods (Source: Bliesner and Lamarra 2000). Colorado pikeminnow are known to spawn later in high-flow years when water temperatures are cooler (Trammell and Chart 1999, Tranunell et al. 1999), and recent studies in the Yampa River found that spawning may be initiated at temperatures of only 160C during some years (Bestgen et al. 1998). It is not known what effect later spawning may have on Colorado pikeminnow, although it would provide less time for YOY to grow during the autumn. Some authors suggested that smaller Colorado pikeminnow are less likely to survive the winter (Haines and Tyus 1990, Bestgen et aI.I998), which may be a major factor in recruitment. Delaying Colorado pikeminnow spawning in the San Juan River also has the potential to place larvae in the rivernear the time ofIate sununer thunderstorm flooding, Platauia et al. (2000) calculated time of spawning for young Colorado pikeminnow collected from the San Juan River during the 7 -year research period, and most spawning dates were in mid to late July on the descending limb of the hydrograph, the typical time for this species to spawn. This suggests that spawning of the existing wild population is not delayed because of cooler temperatures, September 2000 3-41 Program Evaluation Report