Larval Fish Communities Differ Among Great Lakes Rivermouths

We investigated spatial and temporal variation in larval fish communities during 2011-2012 in four Great Lakes rivermouths having different watershed and thermal conditions. Sampling was conducted every two weeks from ice-out through midsummer using paired bongo nets, with sampling occurring in the river, rivermouth, and adjacent lake waters. We found substantial community-level differences among rivermouths; rivermouths with intact watersheds supported cyprinids, while a river with an agricultural watershed was dominated by clupeids. Highest diversity was found in a drowned rivermouth where the mixing zone occurred in a sheltered enclosed embayment. However, all rivermouths supported a mix of both riverine and lake species. Rivermouths were important nursery areas, likely because they supply nitrogen and phosphorus from the watershed and labile carbon from lake sources.