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430 300 200 .., ,.., en ~ ,5 W (!) IX <( I U 300 <n i5 200 100 The Southwestern Naturalist vol. 35, no. 4 Y AMPA RfVER 25 20 .. ., G 0 w IX ::> I- <( IX w 25 0- GREEN RIVER ~ w I- 20 .. ., MONTH FIG. 2-Relationship between spawning period, dis- charge, and river temperature for razorback sucker, Green and Yampa rivers, 1987 to 1989. Q = average daily discharge (United States Geological Survey rec- ords, Yampa River at Deerlodge park, Colorado; Green River near Jensen, Utah; 1989 discharge data are pro- visional); T = average daily temperature (United States Fish and Wildlife Service thermograph, Yampa River at Echo Park; Green River at Jensen). Vertical lines delineate spawning period. ripe females indicated they were ripe for only about 8 days (range of 2 to 15 days). Twenty-seven razorback suckers in breeding condition were recaptured in the same spawning reach in different years (22 males and four fe- males in the Jensen site and 1 male in the lower Yampa River). Six of the Jensen fish were re- captured at that site in 3 different years. Some ripe fish were recaptured at different spawning sites within and between years (n = 6; five males, one female). Ripe flannelmouth and bluehead suckers were captured in the same riffles yielding ripe razor- back suckers. In 1989, flannelmouth and blue- head suckers were each eight times more numer- ous than razorback suckers at the Yampa site, and flannelmouth sucker was twice as abundant as razorback sucker and four times as abundant as bluehead sucker at the Jensen site. Ripe flan- nelmouth and bluehead suckers were captured over a longer period (i.e., 45 days and 42 days for flannelmouth and bluehead suckers, respec- tively) than razorback suckers, and spawning of all three species overlapped between mid-April and late May at both Yampa and Jensen sites. Seventeen suspected flannelmouth sucker x razorback sucker hybrids in breeding condition (14 ripe males, three ripe females) were captured with ripe razorback, flannelmouth, and bluehead suckers in Yampa Canyon (km 0 to 72) and upper Green River (km 478.4 to 499.2). These putative hybrids were intermediate in morphology be- tween the two species based on skull, mouth, and nape characteristics. The most upstream capture of a suspected hybrid occurred in Yampa Canyon about 67.2 km upstream from the confluence with the Green River. Movement Patterns-Some razorback suckers (eight radiotagged, 58 recaptures) remained or were recaptured within a restricted river reach and were classed as local. Most of these fish (n = 59) used the Jensen site, but six used a reach from Island Park to the confluence of the Yampa River (km 524 to 552), and one remained in the lower Green River (km 88 in 1984 and km 126.4 in 1987). Migratory fish (seven radiotagged, 12 recaptures) ranged in movements from 52.8 to 190.4 km. Two radiotagged fish not contacted during the spawning period moved 44.8 and 60.8 km, respectively, between their autumn location and July contact. One recaptured fish had only a line remaining from which the tag was lost. Two movement patterns were identified from radiotracking and recapture data. Thirteen ra- zorback suckers moved upstream or downstream between the Jensen site and Ouray (including Old Charley Wash and the lower Duchesne Riv- er, average one-way movement = 94.4 km, range of 54 to 106 km). Five of the 13 fish were radio- tagged, and continual contact with three fish in 1988 indicated movements of about 7 km/day (78.4 km in 15 days, 97.8 in 20 days, and 99 km in 10 days). The fourth fish made a round-trip movement of 153 km between 5 May and 2 Au- gust 1988, and the fifth fish was intermittently contacted but moved 87 km downstream between early October 1987 and late June 1988. The fifth fish was previously collected in Old Charley Wash (ripe male) on 28 May 1986. All movements (13 fish total) occurred during or following the spawning season and were presumed associated with spawning migrations (nine fish, seven males and two females, were collected ripe during the movement period). A second pattern included ~