Reaction distances of salmonids, scaled to detection distances of scuba divers, for use in a general piscivore foraging model


Category:  Fisheries and Wildlife
Linked Publication
Language: English
Author(s): Jason L. Vogel
Description: The influence of predation on dynamics and structure of aquatic communities has been well documented; however, little is known about how large pelagic predators hunt and detect prey. Visual predation offers the most effective foraging strategy in limnetic systems because vision provides greater search volume and more precise orientation to the prey than other sensory systems. An encounter rate model is needed that combines prey densities and search volumes to determine how many prey should be detected per unit time. Most studies on visual foraging by fish have focused on reaction distances to invertebrate prey; however, when applying these acuity-based results to piscivores reacting to prey fish, reaction distances have been grossly overestimated. Since search volume is the product of swimming speed, foraging time, and reaction distance, visual foraging models are very sensitive to changes in reaction distance. Therefore, before this approach can be generalized to other pelagic predator-prey systems, species-specific measures of reaction distance and in situ measurements of how prey detection changes under different optical conditions are needed. In laboratory experiments, we quantified reaction distance of adult lake trout Salvelinus namaycush to prey fish (rainbow trout Oncorhynchus mykiss and cutthroat trout Oncorhynchus clarki) as a function of light intensity (0.17-261 lux) over three prey sizes (55-, 75-, 139-mm) and three turbidity levels (0.09, 3.18, and 7.40 NTU). Reaction distances increased rapidly with increasing light from <25 cm at 0.17 lux to a threshold (over 12-18 lux) at approximately 100 cm, declined exponentially with increasing turbidity, but were not affected by prey size.