Effects of Waterfall Dimensions and Light Intensity on Age‐0 Brook Trout Jumping Performance

Abstract

AbstractWe conducted three experiments to understand the effects of (1) waterfall design (width, height, and plunge pool depth) and (2) light intensity on the ability of age‐0 brook trout Salvelinus fontinalis to successfully jump over small waterfalls or vertical obstacles, such as pool‐and‐weir fishways. We measured the jumping performance of brook trout as a function of waterfall height (2–24 cm), plunge pool depth (8–18 cm), and fish size (total length (TL), mm). Waterfall height and TL had the largest effects on jumping performance. Maximum heights jumped decreased as waterfall height increased or TL decreased. Our second experiment measured the effects of waterfall widths of 10, 20, and 30 cm on age‐0 brook trout jumping ability for a fixed waterfall height of 20 cm and a plunge pool depth of 40 cm. Significantly fewer fish jumped through the 10‐cm‐wide waterfall than through either the 20‐ or 30‐cm‐wide waterfalls. Our third experiment measured the jumping success of brook trout at light levels of 0, 0.23, and 1.70 lx/μA. Brook trout successfully jumped over 4‐ and 20‐cm‐high waterfalls at all light intensities, providing evidence that they can see very well under low light conditions and may also use senses like the acoustico‐lateralis system to help them negotiate obstacles. We conclude that narrow waterfalls with heights more than three body lengths and shallow plunge pools will probably restrict the movement of age‐0 brook trout, while light intensity does not appear to have much of an impact on their movements.