TOPOGRAPHIC INDEX MODELING OF YOUNG-OF-YEAR BROOK TROUT (SALVELINUS FONTINALIS) HABITAT AND SELECTING CANDIDATE LAKES FOR WILD BROOK TROUT RE-INTRODUCTION

Abstract

Adirondack brook trout (Salvelinus fontinalis) depend on locations of groundwater upwelling for spawning, nursery habitat and thermal refugia for both young-of-year (YOY) and adult fish. Landscape-scale anthropogenic disturbances, such as logging and road construction, have the potential to influence brook trout habitat by altering these groundwater regimes. We used a topographic index (TI) approach to link watershed-scale topography with groundwater-influenced tributaries and seeps and YOY brook trout presence in the littoral zone of three lakes in the Adirondack Mountains, NY. The TI value of shoreline locations was positively associated with the temperature difference between lake surface and substrate, indicating greater groundwater seepage at locations with a higher TI value. The TI value of shoreline locations was also positively correlated with YOY brook trout presence in the nearshore zone. TI represented a significant improvement in predictive capability over currently available groundwater-influenced habitat location and delineation methods. Akaike?s information criterion indicated that TI value was the strongest predictor of: (1) the presence of groundwater-influenced tributaries or seeps, and (2) YOY brook trout presence and numerical abundance in the nearshore zone. However, TI-based metrics were unable to predict brook trout population reproductive status or density at an inter-lake scale, possibly because the effects of acid precipitation are the primary drivers of variability in brook trout population abundance at a regional scale within the Adirondacks. The TI model represents a useful management tool at the scale of an individual lake shoreline, but further refinement is required for applications at an inter-lake scale.