The Effect of Four Light Conditions Upon the Impingement of Year Plus Steelhead Trout, Chinook and Silver Salmon




avoidance behavior, behavior, channel, chinook, flume, flume tests, impingement, light barriers, light conditions, mesh, salmon, screens, silver salmon, steelhead, swimming, swimming time, trout


A total of 12 groups each containing 100 year plus steelhead trout, or chinook or silver salmon were tested under four light conditions in an experimental flume with velocities of 3.0 fps for 45 minutes, and 4.0 fps for the next 15 minutes. The time at which each fish was impinged on the 1/2 inch wire mesh retaining screen at the downstream end of the flume was recorded. The four lighting conditions were: (a) 20 degree angled light barrier across both sides of the flume, (b) 90 degree blocking light barrier across both sides of the flume, (c) all light, and (4) all dark. Steelheads were least and chinooks most dependent upon the light cues to avoid impingement. The 90 degree light barrier and overall light were about equally effective in keeping chinooks and silvers off the screen. The 20 degree angled barrier was successful in deflecting a significant proportion of all three species into the dark channel after they were fatigued, where they were eventually impinged. The total swimming time before impingement was shortest in the dark for the chinooks and silvers, and least with the 90 degree barrier for the steelheads. The experimental condition productive of the longest swimming time for the chinooks and silvers was the 90 degree barrier and all light (no significant difference between them) and all dark for the steelheads (not significantly different from all light). On the basis of the avoiding response to the angled barrier, the steelhead were the most sensitive to light stimuli.

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