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tween fish habitat and river flows. An appar- ent incompatibility between heterogeneous habitats used by squawfish and hydrologic data collected as input to the modeling effort was presented by Tyus (1988). IFIM!PHABSIM modeling must be considered experimental until input variables reflect factors limiting populations of this or other warm-water speaes. Upper Main-stem Colorado River Much research has been conducted on habitat needs of Colorado squawfish in the Upper Colorado main-stem from Lake Powell to Palisades, Colorado (Valdez et a1. 1982b; Archer et a1. 1985, 1986; Wick et a1. 1985; Kaeding and Osmundson 1989). Low num- bers of fish and apparently marginal habitats have hampered development of in-stream management options, as indicated by Valdez et a1. (1982b) and Kaeding and Osmundson (1988a, b, 1989). Habitat alteration by con- struction of water-development projects has been implicated as a major factor in low num- bers of squawfish in the stream Uoseph et a1. 1977; Holden 1979); average water tempera- tures there were judged only 71% as suitable for the species as those in the Green River (Kaeding and Osmundson 1988b). Blockage and other subsequent alterations of upstream habitats in the Gunnison and Colorado rivers above the presently occupied reach may have already removed habitats requisite to support a large adult population. At present, the USFWS is evaluating the need for habitat management in 24 km of the upper Colorado above Grand Junction, Colorado, and has provided preliminary flow recommen- dations for that reach for enhancement of sum- mer discharges for adults. No other specific habitat management plans have been devel- oped. More optimal conditions for spawning and rearing are desirable because abundance and growth of age-o fish are low (Kaeding and Osmundson 1989). The Colorado Squawfish 395 San Juan River Colorado squawfish in the San Juan River have recently been evaluated for their signifi- cance to the overall recovery effort (Meyer and Moretti 1988; Platania and Bestgen 1988; Platania et a1. 1990). However, the fac- tors limiting those stocks are unknown, and development of habitat management options awaits future studies. Habitat Development and Maintenance Development and maintenance of new habitat and provision of access to new areas are con- sidered high-priority recovery goals (USFWS 1987a). The first category includes applica- tion of experimental techniques to existing areas to determine if artificially created habitat will be acceptable for use. This includes con- struction of artificial spawning channels, or conversion of existing (but not currently suit- able) stream reaches to spawning habitat, con- struction of nursery areas, and other efforts. The second category (e.g., construction of 6sh passageways) includes opening up new areas or restoring access to reaches now blocked by dams, diversions, and so on. Colorado squaw6sh migrations have been observed for more than a hundred years, and we have documented travel of hundreds of kilometers in which adults occupy flat-water sections of rivers in autumn, winter, and spring but migrate to whitewater canyons to spawn in summer. Construction of dams, in- cluding Flaming Gorge Dam on the upper Green River and Taylor Draw Dam on the White River, blocked the passage of migrating fish, as evidenced by their congregation below the obstructions prior to the spawning season (McDonald and Dotson 1960; Seethaler 1978; Martinez 1986). These dams were not fitted with passageways for fishes. The only feasibil- ity study was conducted in 1986 by the U.S. Army Corps of Engineers for the Redlands Di- j. I :'!i;I!!~1 I Ii' I. I I, I f; I; ,I" '.,' .'1. .,- ". , i I I