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I~l I I : ~ : ~ I I : ~ ,. I I I' I I I \ I I I'~ I I I I I . : .:'. ~ \..., / .: \ \ .'t /'. :, : :, " , , ,t :' :"'" \ " ' ~.....: ~ '..~:.. \ I \ \/ " :, :' '..t/ '........., ..... ......... '- 10 taken in the more heavily used areas. We made 8 depth and velocity measurements in 1982, 23 in 1983, and 14 in 1984. Near-bed velocity (10 cm above the bottom) was measured only at the spawn- ing sites found in 1983 and 1984. Average stream flow (m3/s) during the spawning period was 85 in 1982, 170 in 1983, and 37 in 1984. Cui-ui spawned over predominantly gravel sub- strate in water 21 to 110 cm deep, where stream velocities were 27 to 140 cm/s and near-bed veloc- ities were 21 to 90 cm/s (Fig. 6). Most spawning was at depths of 71 to 80 cm, at stream velocities of 10 1 to 11 0 cm/s, and near-bed velocities of 71 to 80 cm/s. These depths and velocities were slightly greater than those reported for the June sucker, Chasmistes liorus, by Shirley (1983), and greater in general than those reported for other stream- spawning catostomids (McCart and Aspinwall 1970; McSwain and Gennings 1972; Burr and Morris 1977). Emigration of Larvae Timing of Outmigration Downstream migration rates of young cui-ui were determined by fishing three plankton nets in the 321 30t 22 ~ :2 o 20 1ii ~ 18 III B 16 '0 C 14 Q) ~ 12 Q) a. -; 10 III > ~ 8 ~ .'. ? 6 '3 () 4 2 o ...u..ul__--,'" 5/5 5/12 5/19 5/27 6/3 6/10 6/17 6/24 7/1 7/8 7/15 7/22 7/29 Date fishway or downstream from MB dam. The nets were of l-mm mesh, had a rectangular mouth 43.2 cm long and 30.5 cm wide, and were 115 cm long; the collection bucket was 3.8 cm wide and 10,2 cm long and lined with O.S-mm mesh plastic screen. We fished the nets at the end of the fish- way in 1982 and 1983 (when unusually high flows made it difficult to fish them in the main stem of the river) and below MB dam in 1984, when the river flow was lower. The nets were fished 3 nights per week (Tuesday, Wednesday, Sunday) from 29 May to 30 July in 1982, on alternate nights from 29 May to 14 August in 1983, and on alternate nights from 3 May to 20 June and twice weekly from 21 June to 2 July in 1984. All nets were fished from 2000 to 2400 h and checked hourly. This fishing period was based on catches in 12 24-h periods along the lower Truckee River in 1981 (unpublished data), which showed that emigration was primarily at night. The samples were held until the following morning, and young catostomids from each net were preserved in 10% formalin. We separated cui-ui larvae from those of Tahoe suckers (Catostomus tahoensis) and mountain suckers (c. platyrhynchus)-the other suckers that spawned in the Truckee River-by using a key devised by Snyder (1983). ......... 1982 ----- 1 983 - 1984 Fig. 7. Emigration pattern of larval cui-ui in the Truckee River (1982 and 1984) or the Pyramid Lake Fishway (1983).