Factors Influencing the Efficiency of Light Barriers in the Guidance of Young Salmonidae
barriers, behavior, guidance, light intensities, salmon, silver salmon, steelhead, turbulence
This is the first study completed with the facilities of the new Behavior Laboratory. In a series of 7 factorial experiments, the reactions of 90 different groups of 25 silver salmon were tested to a light barrier in every combination of three angles and three brightness levels, in water with three depths and four velocities. The levels of brightness were chosen in a geometric progression, while the levels of depths and velocities were, for all practical purposes, in arithmetic progressions. The three angles chosen were 25 degrees, 45 degrees, and 75 degrees. The analysis of variance for the different experiments disclosed the following results: (a) The angle formed by the light barrier and the line of current flow is significant at the one per cent probability level or better (except at extreme velocities). The smaller the angle the fewer the number of fish which will enter the lighted area. (b) The intensity of light is significant at a higher level of significance than the angle of the barrier, except at low velocities. Fewer fish enter the lighted area as the light intensity is increased. (c) Velocity has the most distant effect of any of the factors, with the number of fish found in the lighted area increasing with the velocity of the water. (It should be noted that as velocity increases the resulting turbulence and surface agitation reduced the light intensity at the bottom). (d) Depth has not shown any significant effect. The water was so clear that the difference between three inches and 24 inches did not produce a significant decrease in brightness.