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I';; o,f the same Colorado squawfish 00 the same ;;/spawniog grounds over a number of different '::years; fidelity to these specific areas has been ''f::~: demonstrated (Wick et al. 1983; Tyus 1985, ,? 1990; Tyus and Karp 1989). There is no rec- ~fc ord of a fish moving from one spawning reach ~} to the other (e.g., interchanges of Yampa and i;' Gray Canyon fish). Lack of suitable spawning ~; substrate or other factors is not judged to be limiting. Migrating squawfish pass through ~~.. ~any ki!ometers of apparen~ly suitable spawn- .fZ ' mg habitat to reach other Sites, and an olfac- tory homing mechanism was proposed to ac- count for this behavior (Tyus 1985, 1990). Turbidity in the Green and Yampa rivers has precluded direct observation of Colorado squawfish spawning behavior. However, radio- telemetry observations of wild spawning fish were provided by Archer and Tyus (1984), and Hamman (1981) noted behavior of spawning fish in hatchery conditions. Fish behavior was similar to that described for a congener, the northern squawfish (Ptychocheilus oregonen- sis), by Patten and Rodman (1969) and Beams- derfer and Congleton (1982). Northern squaw- fish remained in deep pools or eddies, moved abruptly to cobble bars to spawn, then re- turned to the pools or eddies. This same behavior in Colorado squawfish prompted division of habitats into two types: a resting- staging area in pools or large, shoreline mix- ing (eddying) currents, where fish find suitable resting and feeding conditions between spawn- ing bouts or where males gather around fe- males until they are ready to deposit eggs; and a deposition-fertilization habitat in riffles and shallow runs where they congregate for actual reproduction (Archer and Tyus 1984; Tyus and Karp 1989; Tyus 1990). It has been difficult to identify spawning grounds for Colorado squawfish in otherloca- tions, in part because the fish is so rare. The presence of small larvae in the upper main- stem Colorado and San Juan rivers indicates successful reproduction, but their low num- The Colorado Squawfish 3 8 5 bers suggest limited reproduction or recruit- ment. No conclusive migratory patterns have been detected in the Colorado main stem de- spite years of study, although some migration- like movements have been noted (Archer et at. 1985, 1986). Perhaps spawning behavior documented for the Green and Yampa rivers was disrupted in the Colorado by years of flow and habitat alterations, or perhaps that stream was never optimal for the fish (Kaed- ing and Osmundson 1988b). The San Juan River has been studied far less, and squawfish ecology is less known in that system. Habitat Relations Larval ecology Colorado squawfish larvae hatch in 3.5-6.0 days at 20o-220C (Hamman 1981). Drift net- ting and seining indicate that larvae emerge from the cobble soon after hatching and move downstream out of the Yampa River in three to fifteen days (Haynes et al. 1984; Nesler 1986; Nesler et ale 1988). Drifting young are predominantly protolarvae, and those from shoreline backwaters are metalarvae (Haynes and Muth 1982, 1984), suggesting that the fish seek warmer and more productive habitats as they grow (Tyus et al. 1987). Young-of-year (postlarval) squawfish are rare in Yampa and Gray canyons but are distrib- uted 100-250 km downstream a few weeks after the spawn (Fig. 19-3; Tyus et at. 1982b, 1987). They occupy shallow, alongshore, ephemeral embayments (backwaters) formed in late summer by receding water levels (Hol- den 1977b; Tyus et a1. 1982b, 1987; Haynes et al. 1984; Tyus and Haines 1991). This obser- vation led to development of a downstream transport hypothesis (\v. H. Miller et al. 1982b; Tyus et a1. 1982b). Although the downstream movement of young away from spawning sites was once debated (Holden 1977b; Holden and Wick 1982), the hypoth- esis is now generally accepted (USFWS 1978b,