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upstream reach of the Colorado River would be to establish an adult population that would participate in spawning within available spawning habitat in either upstream or downstream reaches. Its contribution to recovery is guided by the following hypothesis. The upstream reach above Palisade would probably serve primarily as adult habitat. Colorado squawfish in this reach would probably behave similar to the upstream stock in the Yampa River by demonstrating downstream spawning migrations and return to these upstream home ranges. Hypothetically, the loss of the historical population in this reach may be explained by the presence of the instream barriers, particularly the Highline Diversion dam. These barriers serve to effectively block adult fish during seasonal movements, especially spawning migrations in either direction. If primary spawning of the species occurred below the barriers, the upstream stock would have been rapidly depleted of adults migrating downstream and over the barriers to spawn. If primary spawning of the species occurred upstream of these barriers, larval drift would likely place young-of-the-year below these barriers and effectively block recruitment to the adult population. Over time, the upstream populations would diminish through attrition of adults and lack of recruitment. Adult squawfish located downstream of the barriers would be denied access to the upstream spawning site and be forced to seek secondary sites below the barriers. Assuming that fidelity to a spawning site is characteristic of this species, some segment of the downstream stock that normally used this upstream spawning habitat would also be adversely affected and likely diminish in numbers. Reintroduction and successful establishment of an upstream adult squawfish population would still be subject to the negative effects described for the barriers, but would provide a re-enactment of historical status of the species. Subsequent sampling within this study would permit testing of the migration/recruitment barrier hypothesis and results would provide necessary information on the need for fish passage. Successful reintroduction of a population would also provide adequate numbers of "wild" fish to effectively field test or refine design of any passage devices installed, Too few fish appear to exist in the present occupied range to effectively field test any device installed at either Palisade or Redlands. The role of the current occupied reach below these instream barriers as adult and nursery habitat could also be re-evaluated with the upstream populations serving to augment the adult spawning stock throughout. Reintroduction at several sites containing suspected spawning habitat may also serve to better define actual spawning habitat available.