Diversity in Habitat Use and Trophic Ecology of Brook Trout in Lake Superior and Tributary Streams Revealed Through Stable Isotopes

Abstract

Two distinct types of brook trout Salvelinus fontinalis have been hypothesized to occur in Lake Superior: large fish that inhabit Lake Superior for much of the year but spawn in tributary streams, and small fish that are resident in tributary streams. The lake type has declined markedly in range and abundance, and a greater understanding of the behavior and ecology of these populations is needed to support conservation efforts. Comparisons of stable isotope (δ¹³C and δ¹⁵N) signatures between fish caught in the lake and those captured in streams supported the hypothesis of relatively distinct types differing in habitat use and trophic ecology. Comparisons of δ¹³C values for brook trout, other fishes, and aquatic invertebrates collected from stream, stream-mouth, and lake habitats suggested that large-type brook trout are lake specialists, whereas small-type brook trout are stream specialists, stream–lake generalists, or some mixture of the two. Delineating the diversity in habitat use and trophic ecology of Lake Superior brook trout represents a crucial initial step toward understanding the mechanisms responsible for the observed phenotypic diversity and for developing science-based plans to conserve or restore this diversity.

ACKNOWLEDGMENTS

This project was conducted in partnership with the Centre for Northern Forest Ecosystem Research (OMNR Applied Research and Development Branch). We thank J. George, K. Cullis, M. Chase, and R. Swainson (OMNR) and staff at the Centre for Northern Forest Ecosystem Research for field and technical support; R. Cunjak (Canadian Rivers Institute, University of New Brunswick) for providing advice in interpreting the stable isotope analyses and for reviewing this manuscript; T. Jardine (Canadian Rivers Institute) for guidance in stable isotope analysis interpretation; C. Coppaway and R. Bobrowski for assistance in the field; and the Moore, Dupuis, and Ray families for logistical support. Funding was provided by OMNR through the Canada–Ontario Agreement Respecting the Great Lakes Basin Ecosystem, the Great Lakes Fishery Commission Fishery Research Program, a Natural Science and Engineering Research Council Postgraduate Scholarship to M.M.R., and a Natural Science and Engineering Research Council Discovery Grant to R.L.M. All research was conducted in accordance with Animal Utilization Protocol Number 05R070 (University of Guelph).