Ecological factors affecting muskellunge (Esox masquinongy) reproduction in Midwestern lakes

Abstract

Reproduction of muskellunge Esox masquinongy has failed in many waters that formerly supported self-sustaining populations. Laboratory experiments were conducted to isolate causes of such failures. Differential mortality was observed in lots of muskellunge eggs incubated in jars of unaerated lake water over substrates of sand, gravel, silt, aquatic macrophytes, wood, tree leaves, polyethylene screen, and bare glass. High and rapid early mortality (days 1-2), attributable to low dissolved oxygen (DO) concentrations (0-0.1 mg/liter), occurred among eggs incubated on leaves and macrophytes. After day 3, Saprolegnia sp. fungus was implicated in high egg mortalities in jars with inorganic substrates and moderate DO (3.8-4.1 mg/liter). Lowest mortality rates occurred on organic substrates (silt and wood) amidst intermediate DO concentrations (0.4-1.7 mg/liter) and limited fungal infestation. Measured DO at the substrate-water interface in eight midwestern lakes showed that four lakes had high DO (mean, 6.0-8.4 mg/liter), little microstratification, and support self-sustaining muskellunge populations. The other four showed extreme DO microstratification and virtual anoxia (mean, 0.4-2.4 mg/liter) at the substrate-water interface. Populations of these four lakes are almost solely supported by stocking. Qualitative and quantitative observations of spawning areas in the eight lakes showed that suitable spawning area characteristics include substrates with low biological oxygen demand, dense stonewort Chara sp.