Coarse woody habitat addition increases fish community production

ABSTRACT Structural habitat in lake littoral zones is being degraded and lost due to lakeshore residential and watershed development, which can negatively affect fish communities. Coarse woody habitat (CWH) additions are a common structural habitat enhancement tool used by fishery managers to restore degraded or lost littoral habitat and to supplement resource availability and refugia for fish communities. Coarse woody habitat additions potentially provide a pulse of allochthonous carbon and nutrients to fish communities through slow, natural decomposition and bottom-up energy transfer. Yet it remains unknown the extent to which CWH additions increase fish productivity (P) relative to aggregating fish. We initiated a large-scale CWH addition experiment on Sanford Lake, Vilas County, Wisconsin in 2015, with the primary objective of testing whether CWH additions increase fish community biomass (B), P, and P/B (i.e., biomass turnover rate). Pre-manipulation monitoring of the fish community was conducted during spring 2015–2018. In summer 2018, we added 140 full-sized trees to about one-quarter of the littoral zone of the lake and monitored secondary P rates of the entire fish community through 2024. Fish community B and P significantly increased, and P/B increased by 25% post-CWH addition. Overall, fish community P increased from about 3.6 kg/ha/year to 8.2 kg/ha/year primarily driven by B and P for Bluegill Lepomis macrochirus. We observed minimal short-term B and P responses from higher trophic level fishes (i.e., Muskellunge Esox masquinongy, Smallmouth Bass Micropterus dolomieu, Walleye Sander vitreus) post-CWH addition. Our results confirm that CWH additions to low productivity north-temperate lakes not only aggregate fishes, but also enhance fish community P, which should be broadly applicable to other oligotrophic systems where littoral habitat has been degraded.