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II II I II II II II II II II II II II II II' I I I I 3-4 3.2.3 Young-Of-The-Year ~ total of 509 young-of-the-year (YOY) Colorado squawfish were handled during the 6 Cataract trips. A summary of the yay captured is presented -in Appendix B. Of the 509 yay fish handled, 283 were returned alive and 2;~6 were preserved to verify identification. Most of the fish that wel"e preserved were captured in their larval and early juvenile stages when field identification was impossible. All fish that could not be positively identified afield were sent to the Larval Fish Laboratory in Fort Collins, Colorado. That facility issued three reports on the spec imens examined. These reports are incl uded in Appendix C of this document. the was ale Estimated Hatching Time. Also included in Appendix B is an estimate of number of days from hatching to capture for each individual yay. This calculated by applying length/age regressions developed by Haynes et (1985). The relationships are as follows: REGRESSION A: For fish with a total length of less than 22 mm. Age = -76.7105 + 17.4949L - l.055L2 + 0.0221L3 (r2 = 0.99) REGRESSION B: For fish with total lengths of 22.0 to 47.0 mm Age = -26.6421 + 2.7798L (r2 = 0.99) When the estimated dates of hatching are plotted on a frequency histogram (Figure 2), it becomes evident that in 1985, hatching of Colorado squawfish was spread out over a considerable period of time. Some of the variation seen in Figure 2 might be attributed to differential growth rates or slight errors in length measurements afield, but the number of observations indicate that hatching began in late June, peaked on July 1, and continued through the first week of August. Al though 1985 da ta for yay squawfi sh from other reg ions of the Upper Basin are not available at the time of this writing, a comparison of the data from Cataract Canyon is made with predicted hatching dates for Colorado squawfish on the Yampa River for 1980 through 1984 (Figure 3, Haynes et ale 1985). The figures represent hatching times and not spawning times (personal communication with Bob Muth, December 10, 1985). A correction factor of 3-5 days can be appl ied to the predicted hatching times to represent pred icted spawni ng times, - si nce Hamman (198l) reported incubation times were 90-121 hours at water temperatures of 20-24 C. Assuming that the 1980-1984 data represent normal hatching times for the species in'the Yampa River (mid to late July and early August), it can be hypothesized that squawfish found in Cataract Canyon hatch earlier because of warmer water temperatures lower in the subbasin. In 1985, the YOY squawfi sh handl ed in the Cataract Canyon area had hatched primarily the first days of July.