Larval Fish Communities Upstream and Downstream of Spawning Habitat Improvements in the St. Clair-Detroit River System

Three projects to enhance lithophilic spawning habitat in the St. Clair River, Michigan were completed in 2012 and 2014, adding a total of 6.5 acres of rock-reef habitat. To assess fish use of these reefs, larval fish monitoring occurred post-construction upstream and downstream of the reefs.  We used benthic D-frame nets to sample drifting larvae during nighttime and depth-stratified conical nets to sample larvae throughout the water column during day and night.  More fish were captured downstream in the D-frame nets, but catches in depth-stratified conical nets were not as consistent. Composition of catches was variable between depths and in relation to the constructed reefs, however at least one key species, lake sturgeon was typically captured in higher numbers downstream of the constructed reefs.  Other species captured include rainbow smelt, burbot, Coregonus spp., catostomids, and sculpins. Overall densities of larval fish were consistently higher at the surface compared to the other depths for depth-stratified conical samples. These results verify the use of the restored spawning habitat by target species and provide information about the vertical distribution of larval fish in the water column to guide surveys focused on specific species and their use of the St. Clair-Detroit River System.