Numerical and behavioural response of cyprinids to the introduction of predatory brook trout in two oligotrophic lakes in northern Ontario

Abstract

Response of potential prey to the introduction of piscivores in a whole ecosystem is generally inferred from small-scale studies. Using distance sampling, two lakes that were initially without predators and three control lakes where predators were previously present were examined for the response of prey species to the introduction of brook trout (Salvelinus fontinalis). Responses monitored included numerical changes in abundance, changes in habitat use patterns, and changes in the mean shoal sizes of potential prey species. No statistical changes in abundance or habitat use patterns were detected, whereas there was a significant increase in the mean shoal sizes of potential prey species in lakes where predators were added. We conclude that, in some natural systems, shoaling may be the first response potential prey initiate to reduce mortality risk. © 2007 The Authors Journal compilation 2007 Blackwell Munksgaard.