Modelling and Evaluating Suitability of Esocid Habitat in Response to Changes in Water Levels of Georgian Bay (Lake Huron)

Abstract

Muskellunge (Esox masquinongy) and Northern Pike (E. lucius) are ecologically and economically important fish species that rely on coastal habitats in Georgian Bay, especially coastal marshes. These habitats have adapted to the high natural water-level fluctuations of Lake Huron but are threatened by changing water-level conditions associated with global climate change. The overall goals of this thesis were to identify important esocid habitats and understand how their suitability will be affected by changing water levels. First, I used tracking information from radio telemetry studies of esocid populations in spatially distinct regions of Georgian Bay to identify important habitats during breeding and non-breeding seasons. I documented the strong affinity of Muskellunge to re-use specific spawning grounds close to known nursery habitat in coastal marshes. Both Muskellunge and Northern Pike used coastal marshes during the non-breeding season, and physical habitat structure was a more important driver of habitat use in the summer months than water temperature. Next, I created a GIS model using only hydrogeomorphic features (depth, slope, and wave exposure) to map the extent of coastal marshes throughout eastern and northern Georgian Bay to assess how habitat would shift under a range of possible lake elevations scenarios (175.5 – 177.5 m). The geomorphology at low lake levels favoured large areas of shallow (< 0.5 m) habitat at the expense of deeper habitats (0.5 – 1.5 m) that can support an aquatic vegetation community more suitable for young esocids. I used a similar approach to develop a Resilience Index to rank coastal marshes according to their resilience/vulnerability to stable low water levels, for use as a regional screening tool to identify critical esocid habitat. This research advances the understanding of the effects of water levels on coastal marshes and provides applicable tools to assist in conservation and management of these important recreational fisheries.