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45 Northcote (1962) suggested that during times of low light intensity (at night or during periods of high turbidity), fish larvae lose their rheotactic orientation (orientation to a current of water) because of reduced visual orientation and are displaced, usually passively, downstream. Pavlov et ale (1968, 1972) and Girsa (1969) observed that rheotactic disorientation is especially evident in the early larval phases, i.e., protolarvae and mesolarvae. They reported that in early larval teleosts, visual orientation is the only rheotropic mechanism operating and as light intensity decreases, there is a concomitant decrease in the critical velocity at which fish larvae can maintain position in a stream. Conversely, as fish larvae develop, tactile orientation mechanisms begin to function and the importance of visual orientation decreases, hence, rheotropism is possible at reduced light intensities. Further, the ability of fish larvae to maintain position in a stream is directly related to body size and musculature/fin development, hence, smaller individuals exhibit a greater tendency to drift than larger, more developed fish. These observations could explain the observed differences in size (TL) of Colorado squawfish YOY collected in drift-nets versus seines. Only protolarvae and early mesolarvae were collected in drift-nets (size range = 7.2-9.3 rom TL), while larger individuals were collected in seine samples (size range = 8.1-29.0 rom TL). For some fish, downstream transport of their larvae might be related to feeding habits. Muller (1978) and Armstrong and Brown (1983) hypothesized that fish larvae drift either as a means to obtain food (i.e., maintain association with high densities of drifting food organisms) or as a consequence of feeding (i.e., fish larvae emerge from the substrate to feed and are swept downstream). They and Clark and Pearson (1980) also suggested that downstream transport of fish larvae might be associated with strategies for reducing predator pressure. Gale and Mohr (1978) speculated that drifting fish larvae (especially at night) resemble bits of floating debris; as such they probably are not readily detected by sight-feeding predators. Finally, Frank and Leggett (1982, 1983), working with capel in larvae (Mallotus villosus) and using ideas in Harper et ale (1961) based on work with plant communities, developed the "safe site" concept as rationale for why fish larvae disperse downstream. "Safe sites" were defined as special areas which provided necessary resources and enhanced individual survival; these areas had high food densities and reduced predation/competition pressures. They reported that depending upon the proximity of "safe sites" to spawning areas, two dispersal strategies were possible: (1) if the probability of finding suitable habitat at a distance from the spawning site was high, then fish larvae were transported downstream into these nursery areas: (2) if the probability of finding suitable habitat locally was high, then the magnitude of larval fish drift was reduced and larvae were retained at or near the spawning area. Nikolsky (1963), Priegal (1970), and Gale and Mohr (1978) observed that a larval drift-dispersal strategy is frequently incorporated into the life cycle of riverine fishes as a means of placing young in adequate nursery/feeding areas. Tyus (pers. comm.) has reported the collection of larval and juvenile Colorado squawfish from Green River (Utah) backwaters below the Yampa confluence, and it is presumed that some of these individuals originated in the lower Yampa River since no confirmed upstream spawning areas in the Green