A Comparison of Trap Efficiencies for Wild and Hatchery Age-0 Chinook Salmon

Abstract

Trap efficiencies for captured wild and hatchery age-0 chinook salmon Oncorhynchus tshawytscha migrating from the South Umpqua River, Oregon, were compared at three trap positions within a pool, where water velocities were relatively high, medium, or low, to determine if differences existed in the capture rates of these two groups of fish. Mean trap efficiencies for wild chinook salmon ranged from 23 to 27% and did not differ significantly among the three trap positions. In contrast, trap efficiencies for hatchery fish ranged from 1 to 26%, and these fish were captured at significantly lower rates when the trap was positioned in areas of lower-velocity water. Trap efficiencies were similar for wild and hatchery fish when the trap was in high-velocity water but differed significantly when the trap was in slow water. Our observations indicated that differences in the behavior of wild and hatchery fish accounted for the differing capture efficiencies. These findings suggest that trap efficiencies should be estimated independently for wild and hatchery fish until it is empirically demonstrated that the respective efficiencies are similar.