Spawning migrations, age and growth, and summer feeding of White and Longnose Suckers in an irrigation reservoir

During the upstream spawning migration in spring 1978 of suckers into an irrigation reservoir diversion canal, the best correlation was between movement and 'stream temperature X discharge.' White Suckers (Catostomus commersoni) remained in the canal longer than Longnose Suckers (C. catostomus), and males of both species remained longer than females. The rates of White and Longnose Suckers returning downstream were 52.4% and 59.2% respectively, indicating high mortality, possibly from predation during spawning. Minimum age of spawning was 5+ for males and 6+ for females of White Suckers, and 4+ for males and 5+ for females of Longnose Suckers. In the lake, both species approached maturity at age 2 inmales and age 3 in females. Annual growth in females was greater than in males after the age of first spawning. Cladocerans, mostly Daphnia, were major food items in the reservoir during the summer 1977, being 33.7% of White Sucker diet and 74.2% of Longnose Sucker diet over a 4-mo period. Tendipedidae were more important for White Suckers, contributing 21.0% of their food volume compared to 4.7% of food volume in Longnose Suckers. Feeding selectivity for Daphnia by both sucker species was apparent.