Behavior of Post-emergent Lake Trout Fry in the Presence of the Alewife, a Non-native Predator

Although predation by non-native alewife (Alosa pseudoharengus) on lake trout fry (Salvelinus namaycush) has been documented, whether or not emergent lake trout fry innately recognize alewives as predators is unknown. This study investigated the behavior of post-emergent, free-swimming lake trout fry in the presence of alewives. Study objectives were to determine (1) if fry respond to the presence of alewives and show an avoidance behavior, (2) if the fry behavior appeared to be innate or learned, and (3) whether alewives will catch and eat post-emergent fry. The influence of alewives on fry behavior and vertical distribution were determined by adding alewives to tanks containing lake trout fry. Fry immediately reacted to the introduction of alewives by fleeing even though alewives showed no predatory behavior. When lake trout fry were introduced into tanks with and without alewives, more fry were distributed near the top and fewer fry near the middle of the tanks with alewives. Predation of postemergent fry occurred immediately in the second experiment. Survival of fry after 5 days in tanks with alewife averaged 57% in contrast to 94.5% in the control tanks. We conclude that post-emergent lake trout fry, while innately able to recognize alewives as a predator and show evasive behavior, are still vulnerable to predation.