Evaluation of Fishway Designs for Downstream Passage of Spring Chinook Salmon and Steelhead Trout Smolts, 1987: Final Report

The stress response of chinook salmon and steelhead trout smolts to passage through three different flumes was tested by assaying plasma cortisol concentrations before and after flume passage. In addition, descaling of fish was recorded before and after flume passage, and the ability of the flumes to pass adult chinook salmon and debris was determined. The three flumes were a corrugated metal flume (CMF), a 4-foot wide baffled flume (BF4), and a 2-foot wide baffled flume (BF2). Each flume was tested under three conditions: (1) at nights, (2) during the day with a perforated metal cover, which reduced the amount of light entering the flume by about half (partially darkened), and (3) during the day with the perforated cover and an additional double layer of black plastic (completely darkened). Plasma cortisol concentrations were not significantly elevated in chinook salmon smolts after passage through any of the flumes (P\u3e0.2, ANOVA). In daytime tests of partially and completely darkened flumes cortisol concentrations were consistently decreased following flume passage. We attribute this to pre-test stress (holding of fish in small tanks) and to the absence of a strong stress response to flume passage. Flume design did not have a significant effect on cortisol concentrations (P = 0.9). Total darkening of the flumes during daytime was beneficial: cortisol concentrations were lower (P = 0.03) in chinook salmon smolts passing through completely darkened flumes than in smolts passing through partially darkened flumes. In steelhead trout smolts, plasma cortisol concentrations were significantly elevated after passage through the flumes, and flume design did have a significant effect (P\u3c0.0001, ANOVA). Cortisol concentrations were most increased in fish that had passed through the BF2, followed by fish that passed through the BF4. The smallest increase occurred in fish than passed through the CMF. Complete darkening of the flumes during daytime tests did not have a significant effect on cortisol concentrations (P=0.4). Plasma cortisol concentrations were significantly higher in daytime than in nighttime samples of chinook salmon smolts held in darkened and undarkened tanks and raceways. This diel cortisol cycle was unaffected by light intensity. The cortisol response to passage through darkened flumes was greater in nighttime than in daytime tests with both species. None of the flumes tested caused descaling of fish. Descaling was measured in two ways: as a mean percent of body area descaled, and as the percent of fish in a sample with greater than 5% descaling in any of 10 body zones. Neither of these descaling measures was significantly increased after flume passage, and flume design did not have a significant effect. When woody debris was introduced into the flumes, a number of pieces lodged in the two baffled flumes. Most of the pieces that lodged in the BF4 were 1.3 to 2.4 meters in length. All debris passed freely through the CMF. Adult chinook salmon (N = 3) passed through each of the flumes in 5 min or less