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I ,i ~ 1 ;i J ~ j ~. ,. t~ i t"l.i<j ~'~ i I j I :j I I I ! . j :c' I .'11 i . i ! 382 Recovery of Long-lived Species ward recovery of the species in the Green River sub-basin, where it is most widely distributed and abundant, and its ecology is best known. Background Information Management options for Colorado squawfish were difficult to develop because its life cycle was so poorly understood. Remote habitats and difficulty in collecting data in the swift, canyon-bound, hostile Colorado River basin also were factors. As late as 1978, the Colo- rado Squawfish Recovery Plan (USFWS 1978b) stated that spawning migrations had not been reported in ten years. Knowledge of spawning areas, nursery habi- tats, and concentration areas was almost non- existent, and they remained poorly docu- mented until the 1980s (Tyus et al. 1981, 1982b, 1987; Wick et al. 1981, 1983, 1985; Haynes et al. 1984; Tyus and McAda 1984; Archer et al. 1985, 1986; Tyus 1985, 1986; Nesler et al. 1988), when new and better tech- nology and sufficient funds enabled acceler- ated research. Relative densities for adults, juveniles, and young have now been mapped, and management strategies have been drafted (Archer et al. 1986; USFWS 1987a). Behavior and responses of the fish to environmental fac- tors have been investigated in hatcheries (Toney 1974; Hamman 1981, 1986, 1989) and laboratories (Berry and Pimentel 1985; Black and Bulkley 1985a, b; Marsh 1985; Pimentel et al. 1985; Karp and Tyus 1990). In addition, efforts were made to accumulate habitat information on endangered Colorado River fishes, including squawfish, for use in stream-flow recommendations (W H. Miller et al. 1982b; Valdez et al. 1987; Tyus and Karp 1989). The Colorado squawfish has a complex life cycle. Coevolving as it did with the depauper- ate ichthyofauna of the Colorado River, this large, predaceous fish is a generalist adapted to large seasonal water fluctuations, low food bases, and changing riverine subsystems (M. L. Smith 1981; G. R. Smith 1981b; Tyus 1986). Cyprinid fishes invaded the New World from Asia in the Oligocene or early Miocene (Cav- ender 1986), and fossil Ptychocheilus are re- ported from as early as Miocene times (Uyeno and Miller 1965; G. R. Smith 1981a; Minck- ley et al. 1986). We must assume that the fish survived by incorporating life strategies to deal with changing climates varying from plu- vial to arid, using migration and long-distance movement for exploiting changing habitats and environmental conditions of the late Cenozoic, and developing adaptations that enabled it to compete and survive until recent times (G. R. Smith 1981a, b; Tyus 1986). As a result, adult, juvenile, and young Colorado squawfish acquired different life-history attri- butes for survival, and they adapted to utilize virtually every habitat available. The adaptability of Colorado squawfish must form the basis for their management to- ward recovery. However, habitat preferences are difficult to ascertain in nature, and fish dis- tributions and abundances are typically used to infer them. As an example, the USFWS has used densities of different life-history stages in designating "sensitive areas" to guide pro- tective and management measures (Archer et al. 1986; USFWS 1987a). In the following sec- tions particular emphasis is placed on statis- tics for abundance, since the development of appropriate management objectives and the success of any management tool can only be judged on the basis of population response. Detailed descriptions of specific habitat parameters are outside the scope of this pre- sentation, but references are supplied where needed. Life Cycle Longevity, age,and sexual maturity Colorado squawfish are capable of living long lives and attaining large sizes. Adult squawfish were the larges rado River, and important attri advantages. Th companied by favor large adl slow growth (tl nine years) ane Colorado SqU3 1.8-m specimer of age. In the I indicated that 42.8 cm TL Wt than 50.3 cm v I I --~ I L Duchesne R. ~ UT Pri ~ ""'-- / San Rafal Fig. 19-3. Map showing spawn migrations of a confirmed and larvae are com!