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heterogeneity effects; Otis et al., 1978:40--50). The model with the second-highest criterion (i.e., the Null model; Mj is also the simplest in that it presumes all members of the population ar> sc:ally at risk of capture on every trapping occasion. Is estimator (Mb) assumes capture probabilities vary with t_-!-% a,. d with behavioral effects (such as trap-happiness, try ?- - The last tw-) models (Jackknife estimator Mh, and ha_ N:L,. ac:?ept that capture probabilities vary b':' individual Movement by season within- and among reaches.---To determine extent of movement by G. cypha within the LCR, capture and subsequent recapture(s) for 1992 were compiled by reach and season (Table 1--3). Because these data reflect numbers of individuals tagged within each reach for a given season then subsequently recaptured, percentages for each reach and season total 100%. For G. cypha tagged at confluence during winter anc subsequently recaptured, 49% (n = 47) were taken upstream in Powell or Salt reaches during winter/spring. Similarly, of those tagged at confluence during spring and subsequently recaptured, 51% (n = 96) were taken upstream during spring/summer. For Powell reach, 18% (n = 7) of recaptures initially tagged there during winter were taken in Salt reach during winter/spring, while 31% (n = 59) of recaptures tagged there in spring were taken at Salt during spring/summer. Overall, 21% of total movements in 1992 (ascertained by mark/recapture) was upstream. Elevated population estimates at confluence in Jariary/February of 1992 (Fig. 1--3b), followed by upstream movement, argue strongly for staging. Estimates at the confluence peaked in early March, then gradually decreased through June. A similar peak occurred within Powell Canyon reach in late March, extended into April, then decreased into June. Population size did not peak in Salt Canyon reach until April; estimates remained elevated through June. The last six months of 1992 were similar to that of 1991 (Fig. 1--3a, 1--3b), with estimated population sizes dwindling through late summer. However, estimates rose again in Autumn, 1991 but remained low during a similar period in 1992. Evidence for downstream movement is less convincing (Table 1--3). Of G. cypha tagged in Powell reach during winter and subsequently recaptured, 21% (n = 8) were taken at confluence in the remainder of the year. Similarly, 16% (n = 30), and 15% (n = 15) of recaptures tagged at Powell in spring and summer, respectively, were taken at confluence in the remainder of the year. At Salt, 16% (n = 33) and 7% (n = 12) of recaptures tagged in spring and summer, respectively, were taken in the two lower reaches over the remaining seasons. Overall, 9% of recaptures in 1992 indicated downstream movement. Table 1--3 primarily reflects population stasis by reach, 6