Effects of light, prey size, and turbidity on reaction distances of lake trout (Salvelinus namaycush) to salmonid prey

Most studies on visual foraging by fish have focused on reaction distances to invertebrate prey; however, these acuity-based results considerably overestimate reaction distances of piscivores to prey fish. In laboratory experiments, we quantified reaction distance of adult lake trout (Salvelinus namaycush) to rainbow trout (Oncorhynchus mykiss) and cutthroat trout (Oncorhynchus clarki) as a function of Light (0.17-261 1x), prey size (55, 75, and 139 mm), and turbidity (0.09, 3.18, and 7.40 NTU). Reaction distances increased rapidly with increasing light from <25 cm at 0.17 1x to about 100 cm at a light threshold of 17.8 1x. Reaction distance declined as a decaying power function of turbidity. By constructing equations that describe the combined effects of light and turbidity on reaction distances, we can begin to model prey detection capabilities of piscivores at any depth at any time of day in natural environments.