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VANICEK AND KHAl\II~H-uSVl!AWFISJl AND C1IlJB LIFE IIISTOHY 20S ," T^III.E H,-~NIII/I/"" "I C%mdo ,'qullwli"h il/ 19S5-1966 y,.(tr-dIlS,H'S rol/u/rd, (;(('(,/1 Nino" 19M 19M -----------~---- ~--- Year-class Year of capture 1955 1956 1957 1958 1959 1960 1961 1962 1963 HJ64 196,~ 1966 1964 3 2 3 4 8 2 7 1 3.57 275 1965 2 2 3 3 7 6 14 4 29 53 42 l!Jlili 1 3 2 2 3 5 2 0 " II 1 560 Total number taken 8 ---------------------------------------------------------------------------------------- 6 7 fish of age VII and older collected were males, Nearly all squawfish of age VII and older were sexually mature. Reproduction of the northern squawfish has been studied intensively in northern Idaho. Jeppson and Plaus (1959) found spawning occurred in lakes and streams in shallow water over rocks when the water temperature neared 60 F. Keating (1961) reported that squawfish in Cascade Reservoir spawned chiefly over large rubble in riffle areas and at lower ends of pools in tributary streams at temperatures of 60 F and above. Casey (1962) reported that male and female squawfish were sexually mature at ages IV or V, but no males older than age V were found, and females continued to spawn until age XII. Spawning was random over rubble or rock, and each female was attended by several males. 9 18 13 23 5 391 336 43 560 of the eight fish in this condition were bony- tails. The length-frequency analysis for young- of-the-year fish in 1%4 and 1%5 (Figure 7) and the presence of gravid and ripe fish in collections suggested that spawning occurred from late June to early July. In 1966, how- ever, the length-frequency analysis (Figure 7) and the presence of ripe fish in the collec- tions indicated that spawning occurred in mid.] une, This earlier spawning period was related to the earlier temperature rise and water-level recession. In all years, the sus- pected spawning period on;urred when the water temperature reached approximately 65 F. The Colorado chilI. sJla wfwd successfully in all 4, years since closure of Flaming Gorge Dam, No evidence of spawning success was found, however, in the Green River aboye its confluence with the Yampa River in ] 964 and 1966, This apparent ahsenee of repro- Several fish in spawning condition were duction was related to lowered waleI' tem- taken in gill nel;;, bllt neither spawning sites peratures due to increased discharges from nor deposited eggs were located, In 1965, the dam during these 2 years (Figure 21. three ripe males and one spent male (ages Water temperatures in the Green HiveI' above V-VIII) and two gravid females and one the mouth of the Yampa were well below spent female (age VII) were collected. In 65 F, the suspected threshold temperature for ] 966, six ripe males and two spent females spawning, Colorado chubs apparently repro- (ages V-VI) were taken. Ripe males had dueed at Lodore in 1%5 when temperature breeding tubercles on their heads and a patterns were similar to tllOse below the bright reddish-orange lateral hand. All ripe Yampa mouth. Y oung-of-the-year were col- fish were collected in shallow pools and eddies lected at Lodore only in 1965, and yearlings over rubble or boulder bottoms covered with were taken there in 1966. sill. Roundtai:s and honytails were taken in All year-classes since 1957 were repre- spawning condition at the same time of year,., sented in the collections (Table <)). Bony- but they were never found together in the tails were more numerous than rOllndtails for same gill.net set.' Their spawning activities, the 1959, 1960, and 1961 year-classes, while therefore, may have been spatially separated the roundtails were more numerous in ]957, but concurrent in lime. In 1965, six of the 1958, and 1962 year-classes. A particularly seven fish collected in or near spawning con- abundant year.c1ass of Colorado chubs was dition were roundtails, whereas in 1966, six produced in 196'1. Colorado Chub