Modeling Fluvial Habitat Suitability for 11 of Michigan's Listed Unionids

In Michigan, 28 of 45 unionid species are considered endangered, threatened, or of special concern. To aid in management of these species, distributions of ten state listed/special concern species and one federally listed endangered species (Epioblasma triquetra) were modeled to characterize habitat suitability within Michigan.  Mussel occurrences provided by Michigan Natural Features Inventory unionid assemblage surveys and Natural Heritage Database (1990-2012) along with a suite of natural and anthropogenic variables were used in Maximum Entropy (MaxEnt) models. Because host fishes are also important determinants of mussel distributions, host fish distributions were also modeled with MaxEnt and integrated into mussel models. Models predicted that 1,274 to 11,205 km of stream habitat would be broadly suitable and 330 to 3,241 km of habitat highly suitable for the 11 modeled unionid species. Stream discharge, host fish habitat suitability, urban land use, and upstream dam density were the strongest model predictors, with E. triquetra being strongly influenced by dams and agricultural land uses. Recent unionid assemblage field data (2013-2015) was used to evaluate model performance.  The combination of modeled unionid distributions along with the identification of important ecological parameters can allow for more informed decisions in conservation planning and management of Michigan’s listed unionids.