A topographic index approach for identifying groundwater habitat of young-of-year brook trout (Salvelinus fontinalis) in the land-lake ecotone

We used a topographic index (TI) approach to link the presence of young-of-year (YOY) brook trout (Salvelinus fontinalis) at groundwater seepage and stream sites in the land-lake ecotone with subwatershed topography surrounding a set of 21 lakes in Algonquin Provincial Park, Ontario. A lakeshore site's TI value was positively related to the temperature difference between the substrate and lake surface, indicating higher TI values were associated with greater groundwater input. YOY brook trout tended to occupy lakeshore sites with relatively large TI values. Groundwater habitat available to YOY brook trout was relatively rare, with only a few sites used consistently on an annual basis. Larger lakes had fewer groundwater habitat sites per unit length of shoreline than smaller lakes. Logistic regression analysis and model selection (via Akaike's Information Criterion) indicated the odds of finding YOY brook trout increased significantly when a site was a stream and, in the summer, when there was a large difference in temperature between lake substrate and lake surface. Most of the stream sites used by brook trout were not on the Ontario base map system but were revealed by the TI approach.