Protected from the Elements: Winter Ecology of Brown Trout in Groundwater Buffered Streams

Winter has traditionally been considered a period of dormancy for stream dwelling trout in temperate latitudes. Seasonal changes including low water temperatures, ice formation, and reduced prey availability from aquatic and terrestrial sources often contribute to reductions in trout growth and survival. Consequentially, winter has rarely been the focus of study by fisheries scientists, and relatively little information is available regarding stream trout during winter. However, because of the potential impact on stream trout growth and survival, winter is an important season for trout populations and of particular interest to fisheries managers. The goal of this dissertation was to examine winter trophic ecology of stream dwelling trout populations, and the potential of groundwater input to buffer stream water temperatures and trout from the environmental conditions typically associated with winter. This dissertation consists of three chapters that contribute towards this goal. The first chapter examines winter diet of Brown Trout by quantifying trout consumption, identifies important winter prey taxa , and compares diet composition among a number of trout populations. The second chapter describes Brown Trout winter growth and condition, and examines the influence of groundwater buffering and trout diet composition on growth and condition. The third and final chapter uses stable isotope analyses to examine seasonal variation in Brown Trout diets, and the position of trout within winter food webs of groundwater dominated streams. My dissertation will help managers predict the potential effects of winter on important recreational stream trout fisheries, and allow informed management decisions incorporating the best available information.