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RESULTS AND DISCUSSION Movement and Spawning Colorado River Colorado squawfish-Twenty-two Colorado squawfish were implanted with radio transmitters in 1982 and 21 fish were implanted in 1983 (Tables 3 and 4). Only one radiotagged fish (No. 2) moved among adjacent river reaches (Figure 3). The pattern of movement exhibited by some fish within reaches were similar between years. Fish from the upper reach were radiotagged and released in upstream or mid reach areas during May and June 1982; one of these fish (No. 20) moved upstream after its release and then moved rapidly downstream to the Black Rocks area by mid summer, whereas others (No's. 8 and 9) moved to the Black Rocks area with no apparent pr for upstream movement. The .remainder of the radio- tagged fish in this river reach exhibited a variety of up-and downstream movements. During 1983, some Colorado squawfish (No's. 26 and 28) that had been implanted with long-term radio transmitters in the Black Rocks area during fall 1982 had moved upstream to the Grand Junction area by May, and one fish (No. 26) was in the Palisade area in August. The apparent seasonal nature of these reciprocal displacements of radio- tagged fish suggests that some movement of adult Colorado squawfish may be related to spawning, and that this movement might occur between the Black Rocks region and areas upstream. These data also suggest that fish captured and implanted with radio transmitters in May and June 1982 might already have moved upstream from the locations that the fish occupied during winter. The rapid downstream movement of some radio- tagged Colorado squawfish to the-Black Rocks area from the upper reach during July and August 1982 might have been a movement toward spawning areas, rather than a post-spawning displacement. The relative abundance of larval Colorado squawfish collected from the Black Rocks area was h igh within mid -August samples (Miller et al. 1983) which would support the hypothesis that a spawning area occurs near Black Rocks. Legget (1977), in a review of the literature on fish migrations, reported that much of the available information suggests that the movements of fishes "involve a continuous optimization of physiological and neurological states in response to a multiplicity of environmental stimuli." The most upstream areas of the upper river reach may not contain good spawning habitat for Colorado squawfish; radiotagged fish might have rapidly left this area as spawning approached in response to some unfavorable "environmental stimuli". Relatively few larval Colorado squawfish were collected from the upstream area of the upper river reach in 1982 (Figure 4), even though many mature-size Colorado squawfish had been collected from this area in July (Miller et al. 1983). Thus, y radiotagged fish which left this area could have moved to better spawning areas, perhaps near Black Rocks. With the exception of one fish (No. 2), relatively little movement was evident for radiotagged fish in the most downstream Colorado river reach -- the upper region of Lake Powell. Downstream displacement of ii