Stocking Success and Habitat Selection of Muskellunge in a Mid-Western Flood Control Reservoir

Muskellunge (Esox masquinongy) stocking success is highly variable and typically low. In Lake Shelbyville, Illinois, limited availability of structural habitat, fluctuating water levels, and stressful water conditions during stocking events have been identified as potential culprits of poor recruitment of stocked muskellunge. Short-term survival of juvenile muskellunge stocked in 2019 was assessed by holding 15 muskellunge (mean total length = 322 mm) within in-lake enclosures (1 x 1 x 2 m) at each of two different stocking locations. To evaluate escapement and quantify habitat conditions experienced by muskellunge stocked into Lake Shelbyville, 25 juvenile muskellunge were implanted with acoustic transmitters and released at each stocking location on the same date as the main group of stocked fish. Passive receivers have been placed throughout the reservoir to detect dispersal outside of stocking locations and potential escapement downriver from the reservoir. Many dead stocked muskellunge were observed at both sites, and all muskellunge held in enclosures died within 24 hours. The factors responsible for the high mortality are not known with complete certainty, however, high pH, moderately high concentrations of ammonia, and warm temperatures in the reservoir during the stocking events may have increased fish stress beyond the level typically experienced during stocking. Surviving tagged muskellunge are being located biweekly along with associated water quality parameters through the fall, winter, and spring to identify habitat selection and availability during seasonal changes in water temperature and level. Information about short-term survival, habitat use, and seasonal movements will be used to provide guidance for muskellunge stocking practice in flood control reservoirs.