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in the FPB came by way of the river; 11,374 were caught in the river trap (Table 1). After two extraor- dinarily wet years, river access was no longer impeded by the Truckee River Delta, and cui-ui abandoned the use of the fishway. Upstream Migration Cui-ui on their spawning migration up the fish- way and into the FPB were collected, counted, sexed, measured (fork length), and checked for tags. The fish were then either released into a backwater area directly above the dam or trucked farther upstream and released into the main stem of the Truckee River. In 1982-84 the cui-ui migration began as early as 9 April (in 1984) and ended as late as 21 June (in 1982), The three migratory runs lasted 48 to 59 days, while water temperatures ranged from 9 to 20oC; however, migration peaked :2: 500 fish per day) when water temperatures ranged from 9 to 170C and daily means were 12 to 150C (Fig. 4). Sub- jective observation indicated that upstream migra- tion was generally stimulated by rising temperatures and dampened by falling temperatures, These responses to temperature seemed to be both sea- sonal and diurnal; over a 24-h period the cui-ui run was heaviest in late afternoon and evening, when 7 temperatures were highest. This relation between water temperature and the spawning migration of catostomids in general has been observed by others (Bailey 1969; Corbett and Powles 1983; Geen et al. 1966) . To enable us to follow migrating adult cui-ui in the river and locate spawning areas, we applied external radio-tags to 57 fish captured at the FPB-8 in 1982, 27 in 1983, and 23 in 1984 (totals exclude 1 fish bearing a transmitter that failed to operate). A stainless steel wire was routed through the base of the pterygiophores and each end was fastened to a plastic harness trailing behind the dorsal fin. Radio-tags were of three sizes; the largest was 60 mm long and 12 mm wide and weighed 20 g. Transmission life was 30 to 60 days. A Smith-Root RF-4 receiver was used to track fish in the field, and a Smith-Root Field Data Logger (FDL-lOER) was set at the FPB to record the date and time when tagged fish dropped over MB dam as they returned to Pyramid Lake. Of the 57 fish tagged (28 males and 29 females), 12-most of which had been tagged late in the run-returned to the lower river over MB dam within a few hours after their release. The rest remained in the stream for 4 days or longer. The radio-tagged cui-ui migrated only short distances after they were released above the dam, After being tagged at the FPB (after they had moved Table 1, Numbers of cui-ui entering the fish processing building (FPB) through the Pyramid Lake fishway and the river trap, 1976-1984. Identifying Total flows Number entering FPB numbers of March through May Through Through ladders in Truckee River Year fishway river modified a (hectare-meters) 1976 0 0 None 9,565 1977 0 0 None 1,172 1978 33 0 1 2,470 1979 139 0 1 4,830 1980 4,984 0 1, 2 19,405 1981 47 0 1-4 9,018 1982 13,804 1 1-4 59,283 1983 5,994 20 1-4 83,653 1984 0 11,374 1-4 32,983 a See Fig. 1 for location ofladders. In ladder I, velocity was reduced in 1978 and turbulence in 1979. Similar modifications were made in ladder 2 in 1980 and in ladders 3 and 4 in 1981.