Morgan Shoal: Underwater Mapping and the Fishes of Chicago’s Forgotten ‘Coral Reef’

Morgan Shoal is a rocky outcrop in Lake Michigan located a couple hundred meters from the shoreline of Chicago. The outcrop is Silurian dolomite bedrock and is the site of the Silver Spray shipwreck, part of which is often visible above water. There are several ongoing or proposed development projects along the Chicago lakefront. Additional information is essential in making informed decisions. Surveys were conducted from August 2015 to August 2016. Nineteen species of fishes were documented. In November, Lake Trout that had recently spawned were common. Whether they spawned over Morgan Shoal or elsewhere is unknown. Longnose Suckers preparing to spawn were abundant in the spring. Yellow Perch were present during all sampling periods. Physical habitat was surveyed by side scan sonar and direct observations by divers. Morgan Shoal is not just a rock. It is a three-dimensional rock outcrop with horizontal surfaces, vertical surfaces, smooth surfaces, crevices, nooks and crannies, surrounded by smaller bits of rubble and boulders and sand flats. This complex habitat heterogeneity, combined with a solid foundation that does not get washed away by Lake Michigan storms, is the basis of the Morgan Shoal ecosystem.