Structural Complexity Influences Littoral Coarse Woody Habitat Selection by Juvenile Muskellunge

Abstract: Coarse woody habitat (CWH) is an important feature of aquatic systems, offering foraging opportunities, refuge from predation, and spawning habitat. Fish abundance and diversity have been positively correlated with the density of CWH in aquatic systems through manipulative or laboratory experiments; however, less is known about how structural complexity of individual CWH units influences fish use. To explore how fish relate to a gradient of available CWH complexities in a field environment, we evaluated selection of CWH complexities by stocked, juvenile Muskellunge Esox masquinongy in Forbes Lake, Illinois, using radiotelemetry. Most (86%) CWH in Forbes Lake was simplistic, consisting of a single trunk with no or few primary branches, whereas only 9% of the CWH was structurally complex, possessing most or all primary and secondary branches. Muskellunge used all available CWH complexities but selected for intermediate complexity, even though that represented only 5% of the available habitat; all other CWH complexity classes either were used in proportion to abundance or were avoided. Selection by Muskellunge of intermediate CWH complexity may represent trade-offs among prey availability, predator foraging efficiency, and refuge from predation. As impounded reservoirs across the Muskellunge range continue to age and lose habitat complexity, managers engaged in habitat restoration should consider the potential effects of CWH complexity on fish use.