The influence of spawning habitat on natural reproduction of muskellunge in Wisconsin

Many of Wisconsin's native populations of muskellunge Esox masquinongy exhi bit declining reproductive success and failing natural recruitment. As a re sult, self-sustaining populations of muskellunge are diminishing. This stud y focused on spawning habitat factors that influence egg development and su rvival and, consequently, the reproductive success of muskellunge. Muskellu nge spawning habitat characteristics in lakes with self-sustaining populati ons were compared with spawning habitat characteristics in lakes that were once self-sustaining but are now maintained by stocking. The hatching succe ss of artificially fertilized eggs was assessed under natural lake conditio ns. Spawning sites were typically marshy areas in water less than 1 m deep. Characteristics of the spawning habitat influenced successful reproduction . Spawning areas in stocked lakes had low dissolved oxygen (DO; 1.2-5.4 mg/ L) at the substrate-water interface, whereas self-sustaining lakes had more variable DO (0.5-9.6 mg/L) with some microhabitats having high DO. Organic carbon content, texture of spawning substrate, and water temperature at th e substrate did not differ between self-sustaining lakes and lakes supporte d by stocking. Fallen logs, stumps, and other wood in spawning areas may in crease egg survival. Muskellunge egg survival over natural substrate was lo w (0.0-1.3%), even in lakes with self-sustaining populations. Col lections of eggs and observations of fry indicated that major mortality occurred aft er egg deposition but before fry reached nursery habitats several weeks aft er hatching.