Mechanisms and Importance of Spillway Escapement of Muskellunge

Dam escapement and emigration over spillways of reservoirs is a known pathway for loss of sport fish that is considered to be a significant management problem. Fish loss over spillways is analogous to mortality in the system with potential negative downstream consequences. Limited previous studies have shown dam escapement to account for losses of significant portions of the sportfish population. However, despite being a well-known problem we have little understanding about the conditions under which muskellunge escapement occurs and what proportion of a population may be expected to escape annually. We conducted controlled laboratory trials to explore and observe escapement behavior under varying levels of light, turbidity, habitat availability, and flow rate. We also conducted field experiments using PIT tag antennas and a weir to obtain data on the timing and environmental conditions associated with escapement, as well as the demographics of escaping fish in three impoundments with varying spillway designs. Laboratory results showed that muskellunge were more likely to escape during the day compared to night. In the high turbidity treatments less daytime and more nighttime escapement occurred in comparison to the no turbidity trials. Behavioral observations reveal that muskellunge are actively approaching and passing over spillways, suggesting that escapement is not the result of passive fish being swept over dams. By increasing our understanding of spillway escapement we can develop both short- and long-term solutions that will improve the management of muskellunge.