Juvenile Anadromous Fish Passage at Howard Hanson Dam and Reservoir, Green River, Washington, 1992

摘要

We evaluated passage of juvenile anadromous fish at Howard Hanson Dam and Reservoir during the annual reservoir refill-and-evacuation cycle in 1992, and compared our findings to a similar evaluation in 1991. In 1992, as in our 1991 study, we monitored passage of juvenile chinook salmon, coho salmon, and steelhead through the dam in relation to reservoir elevation, outflow, and exit flow temperature. We monitored sooner(mid-February) in 1992 than in 1991 (mid-April) to assess possible chinook displacement from release sties. Refill also occurred sooner in 1992 (late march) than in 1991 (late May) due to low snowpack. We fished fyke traps on principal reservoir tributaries to gauge fish movement into the reservoir, and operated hydroacoustic sensors in the dma's exits to estimate total fish movement through the dam. A scoop trap was periodically fished below the dam to identify species composition of emigrants. Overall, movement of anadromous salmonids past the dam in 1992 was characterized by 1) a pulse of fish during the spring months comprised mainly of chinook subyearlings with a moderate number of coho and chinook yearlings, 2) pulses of chinook and coho yearling in early summer with pulses of chinook subyearlings occurring throughout the summer, and 3) a large pulse of both Chinnook and coho subyearlings in October and November. in 1992, we estimated passage at the dam to be approcimately 1,645 yearling chinook, 168,996 subyearling chinook, 7,489 yearling coho, 31,632 subyearling coho, and 32 steelhead smolts.