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Table 2. Dates of e~ deposition, collections of ripe fish, presence of radio-tamed fish on spaxntinggrottnds, and spawit- ingperiod, Colorado sgttatvfish, Yampa River, 1981-88. Spawning period` Egg Ripe Radio-tagged Year depositions fish fishb Total Optimum 1981 19 June-10 July 1982 10-18 July 1983 20 July-5 August 1984 19 July-13 August 1985 27 June-13 July 1986 27 June-5 August 1987 1 l June-16 July 1988 27 June-19 July 1-10 July 10 July-7 August 14 July-18 August 18 July-14 August 27 June-25 July 5-30 July 3-30 June 29 June-b July 20 June-20 July 4 July-8 Augusta 12 July-S August 10 July-17 August 21 June-12 July N/A 9-30 June 20 June-24 July 19 June-20 July 4 July~4 August 12 July-18 August 10 July-17 August 21 June-25 July 27 June-5 August 3 June-16 July 20 3une-24 July 23 June-13 July 8 July-1 August 15 July-10 August 16 July-15 August 25 June-17 July 1 July-2 August 8 June-5 July 25 June-16 July s Dates obtained from back-calculations of larval age using equations in Nesler et al. (198$). b Dates represent first and last appearance of radio-tagged fish on spawning grounds. `Total includes alt indication of spawning activity, optimum is the average of dates for egg deposition, collections of ripe fish, and presence of migrating radio-tagged fish on spawning grounds. d Data provided by Wick et aI. (1982). spawning (e.g., presence of migrating radio-tagged fish on spawning grounds, collections of ripe fish, or calculated dates of larval emergence in spawning reach} and lasted 4-5 weeks. Optimum spawning period was the time of greatest spawning activity, calculated by averaging the dates when radio-tagged fish and ripe fish were present in the spawning reach and back-calculated dates of egg deposition. From 1981 to 1988, spawning requirements of Colorado squawfish were evaluated in the Yampa River spawning reach. The length of the estimated optimal spawning period -about 26 days -was similar for all years (Table 3). Spawning generally occurred earlier in lower-water years -1981, 1987, and 1988 -and later in high-flow years-1983 and 1984 (Table 3). Water temperature and discharge varied between years during the optimum spawning period (Table 3). Water temperatures ranged from 14.5° C to 27.5°C for all years. Average minimum temperature was 19°C and average maximum temperature was 24°C. During optimum spawning period, mean discharge ranged from 25.27 m3/s (1981) to 108.25 m3/s (1982). Vanicek and Kramer (1969) first suggested that discharge and temperature influenced spawning in Table 3. River conditions during optimum spawning period, Calorado squatvjsh, Yarnpa River, 1981-88. Year Water yearn Period of optimum spawnb __ Mean Discharge` Range Water temperature (°C)d Minimum Maximum (mean) (mean) Range 1981 Low 23 June-13 July 25.27 12.37-37.55 19.3 24.8 18.0-25.5 1982 Average 8 July-1 August 108.25 68.77-176.31 19.5 23.3 16.5-27.5 1983 High 15 July-10 August 86.17 41.6-141.22 21.0 24.3 18.0-27.0 1984 High 16 Juty-15 August 71.74 29.43-131.60 20.3 23.8 20.0-24.0 1985 High 25 June-17 July 64.02 28.58-135.84 17.8 22.8 14.5-25.5 1986 High 1 July-2 August 69.82 26.41-145.46 19.5 228 18.5-23.0 1987 Low 8 June-5 July 58.69 23.97-128.20 17.9 22.5 16.5-24.5 1988 Average 25 June-16 July 49.14 15.73-104.43 19.5 23.0 18.0-25.0 s Designation of low-, avers a-, and high-water years based on average annual discharge for 1922-$7: low, <43.15 m3/s; average, 43.15- 77.83 m3/s; high, > 77.83 m~/s (M. Butler, personal communication). b Derived from back calculations of larval age, and contact with radio-tagged adults and collection of ripe fish on spawning ground. `USGS flow records (1981 sum of Yampa River near Maybell, Colorado, and Little Snake River near Lily, Colorado; 19$2-&8 Yampa River at Deerlodge Park, Colorado). Data are daily discharges for optimum spawning period. d USGS flow records (1981 Yampa River near Maybell, Colorado, 1982 Yampa River at Deerlodge Park, Colorado) and hand-held thermometers (19$3--8$, minimum (mean) and ma~cimum (mean) values were calculated from early morning and afternoon temperatures taken on the spawning grounds because a continuous temperature recorder was not present). 10