The role of temperature in the prey capture probability of drift-feeding juvenile brown trout (Salmo trutta)

Cold water temperatures are widely supposed to reduce the food intake of stream salmonids. Although cold temperatures have been documented to reduce swimming ability, digestion and gastric evacuation rates, little is known about how temperature influences the ability of fish to capture prey. We examined the effects of water temperature on the prey capture probability of drift-feeding juvenile brown trout (Salmo trutta) in a laboratory stream. Temperatures ranged between 5.7 degrees C and 14 degrees C. We found significant effects of water temperature on prey capture probability and capture manoeuvre time. The mean capture probability dropped from 96% at 14 degrees C to 53% at 5.7 degrees C. At 8 degrees C and higher temperatures, foraging performances did not differ much among treatments. We suggest that reduced swimming ability could be one of the most important mechanisms for the observed pattern of reduced prey capture probability at cold water temperatures, but prey detection limitations and predator avoidance may play a role. Our results will be of use for bioenergetics-based drift-foraging models, which to date have not incorporated a temperature-dependent prey capture function.