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114 (44) than any area sampled and contributed 73% of the ripe fish (N = 60). The male: female ratio for all years combined was 1. 6 1 : 1. The collection of sucker larvae from quiet shorelines immediately downstream of suspected spawning areas provided additional evidence that razorback suckers spawned successfully in 1984. Razorback suckerlarvae (10.6-13.6 mm long) were tentatively identified at the Larval Fish Labora- tory of Colorado State University by comparison with cultured protolarvae and mesolarvae of the species. Electrofishing captures of ripe adult ra- zorback suckers also suggested that the larvae in the seine samples were of that species, since ripe suckers of other species were not observed in sam- ples until after these larvae were collected. About 31 % ofthe 42 samples (1,085 specimens) included larval razorback suckers (N = 33). The remaining larvae represented numerous other taxa. Ripe razorback suckers have been captured by others (McAda and Wydoski 1980; Wick et al. 1982) in the Green River basin. These captures, and the ripe adults and larvae obtained in this study, confirm successful reproduction. Observa- tions made at these capture locations were similar to those made in reservoirs of the lower Colorado River basin: razorback suckers spawned in shal- low water over gravelly substrates and congregat- ed near inflowing streams (Minckley 1983). How- ever, these spawning activities and those in the Green River basin did not appear to result in suc- cessful recruitment. The large numbers of intro- duced predator species in the Green River (Tyus et al. 1982) may prey on larvae, as observed by Minckley (1983). These species include green sun- fish Lepomis cyanellus, which can suppress native fishes by preying on their young (Lemly 1985). An alternative hypothesis is that successful reproduc- tion decreased after the impoundment of Flaming Gorge Dam in 1962, implicating habitat altera- tion as a major factor in reducing recruitment. Low water temperatures in spring could lower the survival of razorback sucker embryos, and average spawning temperatures recorded in the river dur- ing this study (15-15SC) may not be optimum for hatching. Marsh (1985) documented the best hatching percentage of razorback sucker embryos at 20oC, with significantly lower hatch at 150C, and complete mortality at 5 and 10oC. Movement Movements of the razorback sucker were de- scribed on the basis of capture and recapture data and radio tracking. Sixty-one razorback suckers, TYUS including six previously tagged by others, were recaptured 74 times, representing 21% of the fish captured. Of the recaptures, 39 were made 1-8 years after tagging. This includes data on fish tagged by Biowest, Incorporated, from 1975 to 1978 (P. B. Holden, Logan, Utah, personal communica- tion) and fish tagged by FWS that were recaptured by the Utah Division of Wildlife (S. J. Cranney, Vernal, Utah, personal communication). The re- maining recaptures (35) were made within 1 year of tagging, with the exception of three fish which could be recognized as recaptures by the presence of a line from which their tags had been lost. With exclusion of 19 local recaptures (recaptured once or more within 2 weeks of initial tagging), 24 fish were sedentary and moved less than 10 km over the tagging-recapture interval. The remaining 28 fish were more mobile and were recaptured an average of 59.3 km from their original release points (range, 13-206 km). Only nine fish of this group displayed more than the average move- ment; one moved a net distance of 192 km in 4 years and another 206 km in 5 years. Twenty-one tagged razorback suckers that were recaptured at least once were found at two or more suspected spawning areas. Some fish moved from one spawning area to another within one season, whereas others moved between areas in successive seasons. Fourteen of these fish were captured at both areas in the Jensen reach: 11 fish moved downstream from river kilometer 498 (DNM) to Ashley Creek, and three moved upstream. Five other razorback suckers moved downstream from Ashley Creek to a flooded bottom (Old Charley Wash) near river kilometer 400, and one moved back upstream. One fish moved downstream 136 km from Island Park in DNM to the Duchesne River from 1978 to 1982 and returned 130 km upstream to DNM from 1982 to 1986. The sig- nificance or function of such migrations is unclear, and it is not known whether the ripe fish are stag- ing in one habitat and spawning in the other, or if spawning occurs in both the mainstem and flooded bottomlands. Local movements were demonstrated by one razorback sucker implanted with a radio trans- mitter in April 1980. This fish moved about 6 km downstream of its capture location and into the lower Duchesne River (a suspected spawning ground); it remained in the lower 2 km of the river until flooding occurred in early June, then moved into the Green River in the mixing zone of the two rivers. It was relocated in July near the same area, and slowly moved about 11 km upstream in , ,~ -, , " .