Fish

Shedd Aquarium and the Chicago Metropolitan Water Reclamation District

There are many habitat needs that fish have, which are generally in short supply in urbanized waterways. The presence of porous natural materials such as logs can disrupt current, and also support the growth of periphyton communities- algae, microbes, plankton and etc. Woody debris also offers places for fish to hide and escape predators, and provides shade and cooler waters on hot, sunny days. The root systems underneath the floating wetlands mimic this by blocking current, and providing growing surface for periphyton. As another benefit, the plants also uptake excess nutrients, increasing water clarity, which allows sunlight to penetrate deeper, and ultimately give submerged plants more opportunity to grow and add even more plants and oxygen from the bottom of the river.

Besides structure, fish also often require specific environmental conditions to support their reproductive cycles. Some fish stick their eggs to natural submerged surfaces such as logs or roots, while other fan out sandy or gravely spots on the bottom of the river where they will guard their nests until the juveniles hatch. In order to support these fish, we add submerged modules, which can mimic diverse bottom types, which are largely absent from urbanized rivers in general. In the case of the Chicago River, most channelized portions are several feet thick of sticky, fine organic sediment, which is difficult for most organisms to use.

The Shedd Aquarium and MWRD have been conducting fish surveys in the Wild Mile since 2016, and research biologist Dr. Austin Happel looks specifically at larval and juvenile fish that inhabit the area, as well as tracking larger fish that pass through the canal. When focusing on fish, it is crucial to understand what about artificial floating wetlands they are attracted to, or might find useful. Among other surprising results thus far, in 2020 the MWRD tagged 10 largemouth bass in the Wild Mile, and one was later found having swam past the removed bridge at River Park and made it’s way 30 miles upstream to Skokie Dam!