Informing the design of fish-friendly shoreline retaining walls for freshwater systems

The structural complexity of aquatic habitats is often reduced by the installation of retaining walls designed to stabilize shorelines and decrease erosion. Alternative armoring techniques such as wall panels that imitate natural habitat complexity are being developed, but they require knowledge of how different structural elements are used by fishes with varied body sizes. In this study, we examined the effects of incorporating four distinct habitat features and textures into experimental retaining wall panels on the behavior of bluegill (Lepomis macrochirus) across a range of body sizes, in comparison to a control (plain) panel. The proportion of times that fish spent near the treatment panels generally increased with panel complexity but there was variation among fish size classes, with larger bluegill preferring medium complexity structure and smaller bluegill preferring the greatest level of complexity. We did not observe any differences in times to visit the panels between treatments or size classes. These findings will help inform and refine the design of retaining walls, providing structural habitat complexity to benefit freshwater fishes across a range of body sizes and life history stages.