Identification and evaluation of fluvial habitat for Arctic grayling (Thymallus arcticus) in Michigan

Arctic grayling, once the dominant salmonid in rivers of Michigan’s lower peninsula, have been extirpated from the state since 1936.  All reintroductions since have failed, with the lack of appropriate habitat suspected to be limiting.  Due to advances in GIS technology, evaluating fluvial habitat across large regions from landscape characteristics is a component of many regional assessments.  By considering species-specific habitat requirements, such an approach can be adapted to support their management.  Our project uses a landscape-scale approach to evaluate fluvial habitat in Michigan’s northern lower and upper peninsulas to estimate suitability for grayling.  Based on 1) a literature review of conditions favored by grayling, 2) established relationships between habitat and landscape factors, and 3) river network connectivity, we developed a rating system for habitat conditions based on landscape characteristics including land use, topography, and groundwater delivery.  Our work suggests suitable habitat remains, with connectivity among spawning, feeding, and overwintering habitats being a possible limiting factor.  Field work will occur this summer to confirm results and enhance the rating with site-specific information.  Our results will help determine if and where grayling reintroductions should be attempted, while providing an approach that can be applied to other fluvial species of special concern.