7752 - Laserfiche WebLink

Home Browse Search

Long-term monitoring data strongly indicate to researchers in the recovery program that numbers of larvae and YOY squawfish and subsequent year classes are highest when intermediate (about the long-term average) peak flows occur during spring runoff. Numbers of YOY were substantially lower on years of very high spring flows (e.g., flow peaks of record in 1983 and 1984 at the State line gauge, Figure 4) (Osmundson and Kaeding 1991), owing either to poor spawning conditions or mortality associated with flushing effects of high runoff. However, Tyus and Haines (1991) obseIVed higher recruitment ofYOY on low flow years in the Green River. Low recruitment of YOY on low flow years in the Colorado River may be related to lack of suitable habitat, either for spawning, or rearing or both. An alternate interpretation of Figure 4 is that the extremely high flows of 1983-84 created or rejuvenated substantial amount of spawning habitat which was available but gradually deteriorating during 1985-88. Regardless of how the relationship is interpreted with respect to the peak (1983-84) and low (1982) flow events, it is fairly clear that production of young squawfish can occur over a very wide range of spring flows (Le., the recruitment threshold of YOY is very wide). Like McAda and Kaeding (1991), I conclude that squawfish spawning may be much less site-specific than is suggested by the literature or a very wide range of preferred spawning conditions exist on the spawning bars where squawfish are routinely found (e.g., Cleopatra's Couch Bar on the Yampa; Three Fords on the Green). The life history strategy of squawfish appears to be strongly influenced by the propensity of the larvae and juveniles to drift far downstream from the spawning site; survivors subsequently move back upstream as they mature. Adults, especially large fish (Figure 5), are most commonly found at or near the potamon-rhithron transition zone in the Yampa and Colorado Rivers. Recruitment of adults presumably is lower for cohorts spawned on low flow years, owing to reduced spawning success to start with and increased predation pressure per fish during each subsequent life history stage. Predation on YOY and juveniles may be more intense on low flow years when habitats are confined. The positive relationship between year class strength and peak discharge generally seems to hold for both the Green River and Colorado Rivers (Tyus and Karp 1989, 1991, Osmundson and Kaeding 1991) and also applies to humpback chub in the Grand 14