Smolt Condition and Timing of Arrival at Lower Granite Reservoir
chinook, environmental factors, hatchery, Lower Granite Dam, Lower Granite Reservoir, migration, monitoring, salmon, salmon yearlings, smolt, Snake River, steelhead, survival, time of arrival, trapping
Hatcheries released 9.3 million chinook salmon and 6.3 million steelhead smolts and presmolts upriver from Lower Granite Reervoir for migration in spring, 1984. We operated smolt monitoring traps at Whitebird from March 14 to May 12, Snake River from March 22 and May 15, and Clearwater from March 29 to May 13. Peak passage of yearling chinook salmon occurred the third week in April at both Whitebird and Snake River traps. Passage of steelhead was still increasing when high water stopped trapping in mid-May. Median migration rates for branded chinook salmon between release sites and Whitebird were 3, 17, and 15 miles/day for Rapid River, South Fork Salmon, and Decker Flat smolts, respectively, an average of 11.6 miles/day. Average migration rate for these three groups between Whitebird and Snake River trap was 28 miles/day. Average migration rate between release sites and Snake River (the head of Lower Granite Reservoir) was 13.2 miles/day and from that point on through the reservoir to the dam, 1.9 miles/day. Salmon River discharge, when considered along with other environmental factors, had the greatest effect on migration rate of smolts branded both at hatcheries and at the Whitebird trap and migrating to the head of Lower Granite Reservoir. Migration rate for steelhead released from Dworshak Hatchery and recaptured at the Clearwater trap was 34 miles/day. Survival rates to the Snake River trap of branded chinook salmon smolts released at Hells Canyon Dam, Rapid River, South Fork Salmon, and Decker Flat were 52%, 65%, 68%, and 35%, respectively. Classical descaling, where at least 40% of the scales are missing from at least two of five areas on the side of a smolt, ranged from 0 to 5.3% at hatcheries for chinook salmon and was less than 1% for steelhead. Descaling rate often increased about 1% at release sites. Classical descaling at Whitebird, Clearwater, and Snake River traps averaged 4.5, 2.5, and 1.5% for chinook salmon, 2.1, 0.4, and 1.4% for wild steelhead, and 8.7, 4.1, and 5.5% for hatchery steelhead, respectively. Scattered descaling, where at least 10% of scales are missing from at least one side of a fish, was always more extensive than was classical descaling, ranging from 2.5 times greater for Clearwater hatchery steelhead to 6.8 times greater for Clearwater wild steelhead. Mean total length of chinook salmon yearlings was the same at all the traps, i.e. 128 mm (117 mm fork length) + 1 mm. The largest chinook salmon smolts came from Dworshak National Fish Hatchery on the Clearwater River. Hatchery steelhead were smallest (x = 203 mm) at the Clearwater trap and largest (x = 239 mm) at the Whitebird trap. Wild steelhead were also smallest at Clearwater trap (x = 178 mm) and largest at Whitebird trap (x = 193 mm). Purse seining to evaluate rates of descaling before and after smolts passed Lower Granite Dam was largely ineffective since we were unable to catch sufficient numbers of smolts in the tailrace, and winds in the forebay area altered descaling rates in sampled smolts.