4 May 2021

Monitoring the Milwaukee Harbor Breakwater: An Engineering With Nature® (EWN®) Demonstration Project

Abstract: The US Army Corps of Engineers (USACE) maintains breakwaters in Mil-waukee Harbor. USACE’s Engineering With Nature® (EWN®) breakwater demonstration project created rocky aquatic habitat with cobbles (10–20 cm) covering boulders (6–8 metric tons) along a 152 m section. A prolific population of Hemimysis anomala, an introduced Pontocaspian mysid and important food source for local pelagic fishes, was significantly (p < .05) more abundant on cobbles versus boulders. Food-habits data of ale-wife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) pro-vided evidence that H. anomala were a common prey item. Night surveys and gill netting confirmed O. mordax preferred foraging on the cobbles (p < .05) and consumed more H. anomala than at the reference site (p < .05). H. anomala comprised a significant portion of the diets of young-of-the-year (YOY) yellow perch (Perca flavescens), YOY largemouth bass (Micropterus salmoides), and juvenile rock bass (Ambloplites rupestris) caught on the breakwater. The natural features’ construction on the break-water increased the available habitat for this benthopelagic macroinverte-brate and created a novel ecosystem benefiting forage fish and a nursery habitat benefiting nearshore game fish juveniles. These data will encour-age the application of EWN concepts during structural repairs at other built navigation infrastructure.