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<br />43 <br /> <br />DISCUSSION AND CONCLUSIONS <br /> <br />Based on these results and complementary studies (e.g., Tyus et ale 1981; <br />Wick et ale 983; Tyus 1984a, 1984b; Tyus and McAda 1984), Colorado squawfish <br />reproduction in Colorado appears restricted to reaches of the mainstem <br />Colorado Riv r (Mesa Co.) and lower Yampa River (Moffat Co.). In the <br />Colorado Riv r, spawning occurs above the Colorado-Utah state line to Clifton <br />(L. Kaeding, CRFP, pers. comm.); however, captures of ripe adults and YOY <br />collections ave failed to definitively identify spawning sites and more work <br />is needed. olorado squawfish spawning in the Yampa River is apparently <br />largely rest icted to the lowermost 32 km of Yampa Canyon in DNM (i.e., <br />Harding Hole to Yampa-Green River confluence); the majority of ripe adult <br />fish general y congregate at river km 26-32 (Haynes and Bennett, in press). <br />However, the drift-net collection of one larval Colorado squawfish at Harding <br />Hole in 1983 established that at least limited spawning occurred above this <br />site. <br /> <br />During t is study, Colorado squawfish spawning in both rivers was <br />estimated to have begun in early-late July and typically extended to late <br />July through early August. For all years studied in both rivers, spawning <br />coincided wi h decreasing flow and rapidly rising water temperature; maximum <br />mainchannel ater temperature always approximated or exceeded 20 C during <br />spawning. Dring 1980-1982 (Yampa River), the numbers of Colorado squawfish <br />YOY collecte were too low to make realistic evaluations relative to spawning <br />"intensity"; however, estimated spawning dates for 1983 and 1984 revealed <br />that while 1 mited spawning occurred as early as 11 July and 4 July, <br />respectively (mean water temperature=18-20 C, both dates), a peak in spawning <br />activity occ rred between 25 July-10 August (1983) and 13-23 July (1984) with <br />mean water t mperatures of 22-25 C and 22-23 C, respectively. Hamman (1981) <br />reported an ptimum spawning temperature range of 20-22 C under hatchery <br />conditions. The 1983 estimated peak in spawning activity coincided closely <br />with dates w en radio-tagged adult fish were active over the spawning areas <br />(H. Tyus, CR P, pers. comm). <br /> <br />~ <br /> <br />The role played by water temperature and flow in streams in influencing <br />fish reprodu tion and larval production/survival are inseparable, with flow <br />exerting a d terministic effect on water temperature. Water temperature has <br />been documen ed as an important, influencing factor for several aspects of <br />fish ecology including movement and spawning (Nikolsky 1963; De Vlaming <br />1972). Spa ing commences at a particular water temperature and may continue <br />as long as t at temperature is maintained. For example, Beamesderfer and <br />Bjornn (1980 observed that peak spawning of northern squawfish <br />(Ptychocheil s oregonensis) in Idaho coincided with water temperature of <br />10-15 C and pawning ceased at 16-18 C. They also observed a reduction in <br />spawning act vity following a storm-induced water temperature decline of <br />approximatel 5 C. This latter observation suggests that water temperature <br />is an import nt, regulating factor in Ptychocheilus reproduction. Flow <br />exerts a pro ound influence on fish life cycles and habitats (Nikolsky <br />1963). For xample, flow is important in regulation of the areal extent and <br />preparation/ intenance of spawning and nursery areas, and influences the <br />extent and p ttern (spatial and temporal) of larval fish dispersion from <br />spawning are s. Depending on the mode of reproduction (e.g., lithophilic or <br />pelagophilic , several studies have reported variable responses of year-class <br />strength of iverine fishes to variations in discharge (Turner and Chadwick <br />