Contributions of Drowned River Mouth Lakes to Great Lakes Fish Populations

Freshwater estuaries and drowned river mouth lakes (DRML) are increasingly recognized as important components of the Great Lakes ecosystem.  These connected systems form the interface between the Great Lakes and tributaries, and are important areas for nutrient exchange and fish production. To investigate the potential magnitude of fish production from these systems and the degree of exchange between DRML and Lake Michigan, we measured larval fish abundance in a DRML (Lake Charlevoix) and in adjacent areas of Lake Michigan from 2008-2011.  Larval fish were sampled during May – July using a towed ichthyoplankton net at locations in Lake Charlevoix, the connecting channel (Pine River / Round Lake), and Lake Michigan.  We collected eight species, the most abundant of which were lake whitefish and yellow perch.  Densities of lake whitefish peaked in early May and yellow perch density peaked in June.  Larval fish densities were generally highest at connecting channel sites, followed by DRML sites and Lake Michigan sites.  Our study quantified the extent of exchange of larval production between DRML and the Great Lakes for one system; additional work is needed to determine the contribution of DRML larval production to year class strength in the Great Lakes.