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Habitat Selection Observations on water depth and velocity and the composition of bottom substrates were recorded for most of the squawfish capture sites and for radio tagged squawfish during dial tracking activities. As a result, a massive amount of data has been generated on these three parameters for the different size groups of squawfish and most other species for three seasons of the year. A third body of data were generated under the investigations utilizing the northern squawfish as a surrogate to the Colorado squawfish. The northern squawfish was very common in the Columbia River basin and lent itself well to laboratory experimentation and in situ observation. This work, carried out by the staff of the Idaho Cooperative Fishery Research Unit, has provided some direct observations of the northern squawfish's habitat preferences that correlates well with indirect field investigations of the Colorado squawfish. The life-stages that appear to be the most critical for the Colorado squawfish i~~during the period from the initial spawning act on through v its first year of life. It has been demonstrated that these phases of a squawfish's development are also tied very closely to some very specific habitat requirements and, therefore, perhaps the major reason for their being critical. Spawning is generally a highly vulnerable period for most fishes where a relatively minor environmental change can be devastating to a population's reproductive success. This appears to be true with the squawfish. Our observations pointed out that spawning habitats were very limited and that they must meet some very rigid requirements to be suitable. Only one specific spawning site was identified for Colorado squaw- fish during this 3 year study, but based on young fish a few other areas must exist. The identified spawning area at RM 16.5 on the Yampa River provided an interspersion of rapids and deeper pools. This area provided clean cobble in relatively deep water of moderate current similar to the conditions sought out bq northern squawfish in the St. Joe River for spawning (~aPwap^c^vz'"~°-~= ,i !'nr,p~ ofnn 1 OQ , . la p~P'-~r^ D ~ _a_____~- The migration of several radio tagged adult Colorado squawfish to this one local and the capture of many other ripe adults provided considerable evidence that a major number of adults congregated in this very localized area to spawn. Very similar behavior was observed for the northern squawfish where a major portion of that population spawned at a few, very confined sites. Clearly, a critical key to preserving this species is the preservation of the integrity of these spawning sites and the maintenance of conditions conducive to egg survival. Sufficiently high flows on a regular basis to flush the fine sediment out of the cobble areas utilized for spawning would be a prerequisite for ensuring egg survival.