Using Fish Egg and Larval Surveys to Assess Efficacy of Constructed Spawning Habitats in the St. Clair-Detroit Rivers System

Artificial reefs were constructed in the St. Clair and Detroit rivers to restore spawning habitat for native fishes. Three reefs were constructed: Belle Isle (2004) and Fighting Island (2008) reefs in the Detroit River; and Middle Channel reef (2012) in the St. Clair River. Surveys of eggs and larvae were conducted for one to two years prior and at least two years post-construction. At Belle Isle, egg assessments indicated an increase in deposition by Walleye Sander vitreus, Lake Whitefish Coregonus clupeaformis, and suckers Catostomidae spp. Pre-assessment egg surveys at Fighting Island showed that Walleye, Lake Whitefish, and suckers used the area prior to spawning and continued after construction, but densities were higher adjacent to the reef. No Lake Sturgeon Acipenser fulvescens eggs or larvae were collected in pre-assessments, but were found in post-assessments. Larval fish drift surveys showed production of Lake Sturgeon emanating from the reef. At Middle Channel, Walleye and sucker egg densities were low during pre- and post-construction assessments but Lake Sturgeon showed a marked increase. Larval fish drift surveys were inconclusive because densities were similar above and below the reef. Overall, response to constructed reefs varied across locations and species and warrants continued monitoring.