Lahontan cutthroat trout (Oncorhynchus clarki hensawi) spawning and downstream migration of juveniles into Summit Lake, Nevada

The only remaining self-sustaining native population of lacustrine Lahontan cutthroat trout (Onco rhynchus clarki henshawi) not affected by nonnative salmonids is in Summit Lake, Humboldt Count): Nevada. Annual spawning runs in 1993 and 1994 were monitored at a fish trap on Mahogany Creek, the only spawning tributary for Summit Lake. Number of spawners was similar in both years, with 1290 upstream migrants observed in 1993 and 1255 in 1994. In 19 93, 137 postspawners (10.6% of upstream migrants) returned to the lake, and in 1994, 434 postspawners (34.6% of upstream migrants) returned downstream through the fish trap. Two distinct, groups of subadult Lahontan cutthroat trout were observed moving downstream in 1994. The first group passed down stream between 27 April and 29 July and included 1188 fish (average folk le ngth = 90 mm). Between 1 August and 31 October, 1160 fish (average fork len gth = 42 mm) moved downstream. Size differences of these 2 groups suggest t hat the 1st group comprised fish that had overwintered in Mahogany Creek, w hile the 2nd group were probably young-of-the-year.