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The life history or phenology of the native species may help to explain their observed length-specific drift phenomenon. As newlY-hatched protolarvae, these fish have enlarged yolk sacs and little mObility since they lack distinct fin rays or spines. Having been hatched from eggs deposited in gravel bars, these protolarvae lie in the relatively quiet interstitial spaces of the spawning area. As mesolarvae, the fish still lack fully-developed fins, fin rays, and musculature for full mobil ity. At this phase of development, the yolk sac is nearly absorbed and the mouth and gut are developed for active feeding so that the fish emerge from the interstitial spaces. It is apparently at this developmental phase that many of the young fish become exposed to the river currents and are transported downstream. Some are probably swept invnediately to shore while others are transported varying distances. This drift phenomenon may also serve as an effective feeding mechanism. Even with their apparent limited mobility, diel patterns indicate that these mesolarvae are able to escape surface drift by either descending to the benthic zone or by moving to shorel ine habitats. Their low abundance in shorel i ne hab ita ts sugges ts that many fi sh descend into the ha rd- to-samp Ie benthic zone. In metalarval and juvenile phases, the fish have a nearly full complement of fin.. and fin rays as well as musculature to provide for full mobil ity. It is at these phases that the fishes concurrently dwindle from the dri ft and increase in abundance along the shorel ine. This is particularly apparent for flannelmouth suckers and speckled dace (Figure 5). It is hypothesized that the fish are sufficiently mobile to actively escape drift and find their way to the shel tered shorel ine habitats. ACKNOWLEDGEMENTS We thank Mr. Joel Bich (Parachute) and Richard Valdez (Pal isade) for their efforts in conducting a portion of the field efforts for the studies at these two sites. LITERATURE CITED Banks, J.L. 1964. Fish species distribution in Dinosaur National Monument during 1961-1962. M.S. Thesis, Colorado State University, Fort Coll ins. 96 pp. Gale, W. and H. Mohr, Jr. 1978. Larval fish drift in a large river with comparison of sampling methods. Transactions of the American Fisheries Society. 112:280-285. Geen, G., T. Northcote, G. Hartman and C. Lindsey. 1966. Life histories of two species of Catostomid fishes in Sixteenmile Lake, British Columbia, with particular reference to inlet stream spawning. Journal of Fisheries Research Boanj of Canada. 23:1761-1788. Haynes, C.M., LA. Lytle, LJ. Wick and R. L Muth. 1984. Larval Colorado squawfish (Ptfchocheilus lucius Girard) in the upper Colorado River Basin. Coloardo, 1979-1981:-$OUthwestern Natural ist. 29:21-34. Ho Ide n, P. B. squawfi sh. Co I orado. 1977. Habitat requirements of juvenile Colorado River FWS/QBS-77/65, U.S. Fish and Wildlife Service, Denver, 70 pp. 576