The influence of the prey community on the growth and life history variation of aquatic apex predators in the Canadian Boreal Shield

Abstract

Northern Pike (Esox lucius (Linnaeus, 1758)) and Lake Trout (Salvelinus namaycush (Walbaum, 1792)) are important apex predatory fish species that have ubiquitous distributions across Canada. While these species have been well studied due to their economic value, there remains considerable uncertainty around the influence of prey community dynamics on their growth and life history variation across the Canadian Boreal Shield. I investigated how changes and differences in prey community dynamics of Boreal Shield lakes influence the growth and life history traits expressed by these apex predators to further understand how their life history strategies have evolved, as well as how their life history strategies might shift in the face of environmental change. Broad geographic comparisons among Northern Pike populations revealed evidence for a widespread generalist foraging strategy, one that takes advantage of the availability of offshore Cisco (Coregonus artedi (Lesueur, 1818)). Similar to the offshore predator Lake Trout, Northern Pike reached larger asymptotic lengths in lakes with greater abundances of Cisco. Northern Pike additionally exhibited slower early growth rates and lower mortality rates in lakes with greater abundances of Cisco. In the absence of larger offshore prey fish, Lake Trout growth appears to be strongly influenced by the availability of nearshore prey fish in Boreal Shield lakes. Following an increase in the productivity of cyprinids in an experimental lake, the early growth rates of Lake Trout increased significantly, with the greatest amount of growth occurring after a switch to piscivory at age 2. With a variety of stressors threatening the health and stability of aquatic ecosystems, this research provides vital information pertaining to the influence of prey community dynamics on the growth potential and life history variation of aquatic apex predators in the Canadian Boreal Shield.