Great Lakes Spotted Muskellunge Restoration: Evaluating Natural Recruitment and Modeling Spawning Habitat in Green Bay, Lake Michigan

Abstract

The identification and protection of critical spawning habitat for muskellunge (Esox masquinongy) in Green Bay of Lake Michigan is a vital step for re-establishing a self sustaining population. This study was designed to document the extent of natural reproduction and locate spawning areas using oviduct insertion of radio transmitters into mature females prior to spawning. Expelled transmitters were later located using radio telemetry to identify spawning sites. Between 2009 and 2010, twenty-six of thirty-seven (70%) implanted transmitters were located as deposited at spawning sites. Using identified spawning locations, habitat selection was estimated for key environmental variables, and spatial models were built to predict muskellunge spawning habitat in Green Bay. Menominee River data were utilized in modeling because it had the most documented successful reproduction in Green Bay. Menominee River muskellunge showed a significant preference for spawning in areas with low to moderate bottom slopes (0-3%), medium percent vegetative coverage (34-66%), where woody debris was present, and in substrates containing silt. Utilizing these identified habitat preferences allowed successful modeling of location and characteristics of spawning areas. Two modeling approaches were used, classification tree and Maxent (maximum entropy). Classification tree models predicted areas to be spawning habitat based mainly on bottom slope, woody debris, and submerged vegetation. Maxent models proved most effective at predicting limited areas as potential spawning locations and correctly classifying most known spawning sites. Maxent models used habitat variables of vegetative cover, bottom slope, percent silt, and presence of woody debris as the main variables to identify spawning habitat. Dissolved oxygen levels averaged 5.7 mg/L over all Menominee River spawning sites but levels as low as 3.8 mg/L were observed within specific spawning areas and may cause site specific egg and larval mortality. In the future, habitat preferences and model results could be used to locate suitable locations for stocking muskellunge, guide designations of critical habitat to protect important spawning habitat, and identify areas for rehabilitation projects to enhance muskellunge spawning success.