**The title, authors, and abstract for this completion report are provided below. For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**

Understanding life history and ecology to support the management and conservation of migratory brook trout in Lake Superior

Robert L. McLaughlin², Luis Antonio Vélez-Espino ³, Robert Mackereth ⁴

² Integrative Biology, University of Guelph, Guelph, ON, N1G 2W, 519 824 4120

³ Fisheries and Oceans Canada, Salmon and Freshwater Ecosystems Science Branch, Pacific Biological Station

3190 Hammond Bay Road, Nanaimo, BC V9T 6N7

⁴ Ontario Ministry of Natural Resources, Centre for Northern Forest Ecosystem Research,

Lakehead University Campus, 955 Oliver Rd, Thunder Bay, ON, P7B 5E1

August 2011

ABSTRACT:

We tested predictions regarding the ecology, life history, and movement behaviour of brook trout populations inhabiting the bays and tributary streams along the north shore of Lake Superior to make inferences regarding the migratory behaviour, life history, and population dynamics of these populations. The populations studied are purportedly polymorphic, with large fish believed to inhabit Lake Superior for much of the year, but migrate into tributary streams to spawn, and small fish believed to remain resident in the tributary streams. The large type is the focus of conservation concern due to declines in its abundance and range, and the biology of both types remains poorly understood. A conceptual framework for distinguishing among competing hypotheses that could lead to two phenotypes of brook trout differing in ecology and life history was developed and tested. Four years of field work demonstrated that (i) lake and stream caught brook trout differ in their habitat use and trophic ecology, (ii) lake caught fish grow faster from year 1 on and live longer than stream caught fish, (iii) stream caught fish are typically stream resident and reach sexual maturity while residing in tributary streams, and (iv) fish adopting a stream resident life history do not appear to enter the lake later in life. When combined with earlier evidence that lake and stream caught fish arise from a common population, our data provide strong support for the hypothesis that these populations of brook trout exhibit partial migration, where a fraction of the population migrates from spawning tributaries to coastal areas of the lake and another fraction remains resident in the tributaries where spawning takes place. A model of population dynamics for a virtual population of brook trout exhibiting partial migration was constructed. It indicated that (i) density dependence and environmental stochasticity were needed to maintain partial migration, (ii) density dependence during the juvenile stage was strongly influenced by the return of adult migrants from the lake, which contribute disproportionately to reproduction in the streams thereby creating the density dependence that encourages some juveniles to leave the streams for the lake, and (iii) there are threshold rates of the return for migrant individuals, below which partial migration is no longer viable and the population collapses to a stream resident strategy. Our study demonstrates how rigorous field studies of ecology, life history, and habitat use can clarify the nature of migratory movements displayed by species whose movements are challenging to track over an individual’s lifetime and provides insights into the ecology, life history, and population dynamics of these brook trout populations that managers can use to improve conservation and restoration plans.