Influence of Prey Behavior on Selective Predation by Lake Trout (Salvelinus namaycush) under Laboratory Conditions

We explored whether certain behaviors by prey fish species contributed to selective predation by lake trout (Salvelinus namaycush). Schooling behavior, reactive distance, and predator attack and prey escape swimming speeds were examined for alewife (Alosa pseudoharengus), bloater (Coregonus hoyi), rainbow smelt (Osmerus mordax), and yellow perch (Perca flavescens). In addition, two- and three-prey species combinations were presented to lake trout to determine if a particular prey species was utilized to a greater extent than others and to observe which specific behaviors or other prey characteristics could account for their greater utilization. There was little difference in percent capture of various prey species and no significant difference (p > 0.05) in escape swimming speeds or attack swimming speeds. However, maximum attack swimming speeds by the lake trout exceeded the maximum escape swimming speeds of prey. Average escape swimming speeds ranged from 2.5 to 2.9 m/sec, and average attack swimming speeds ranged from 2.8 to 3.1 m/sec. Reactive distances were not important since more than 90% of the prey were captured before they had time to react. Prey reactive distances ranged from 0.0 to 1.0 m. Even a small reactive distance and an average escape swimming speed allowed the prey to get close to the aquarium wall where lake trout would not attack. In two-species trials, bloater was preferred over yellow perch (p < 0.025) in one trial. In three-species trials, lake trout foraged preferentially (p < 0.05) on alewife when compared to bloater and yellow perch in four of five trials. The bloater appeared as the second most utilized species although there was no significant difference (p > 0.05) in utilization between bloater and yellow perch. Lake trout were probably reacting to the continuous movement and tight schooling of alewives in the water column.