EWN Publications

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

Eric J. Geisthardt, Burton C. Suedel, and John A. Janssen
March 31, 2021

About This Publication

ERDC Technical Report

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 encourage the application of EWN concepts during structural repairs at other built navigation infrastructure.