The Impact of Changes in Water Level and Human Development on Forage Fish Assemblages in Great Lakes Coastal Marshes

Changes in water levels and development of shorelines are expected to negatively affect coastal marshes. The small-bodied fish assemblage was sampled in the inner marsh vegetation zone in five Les Cheneaux bays with differing levels of development. Observations were made from 1996 to 2004 during which time summer water levels varied from 177.2 m to 176.0 m (chart datum = 176.0 m). Each marsh was sampled for 10 consecutive days in July and August using gangs of five baited commercial minnow traps. Assemblage composition was assayed by species richness, the number of native minnow species, the percentage of selected tolerant fishes (bowfin, Amia calva, mudminnow, Umbra limi, common carp, Cyprinus carpio, and brown bullhead, Ameiurus nebulosus), and catch-per-unit-effort (CPUE). There were no consistent relationships between fish assemblage measures and year, water level, annual change in water level, exposure, and water temperature. Fish assemblage measures except CPUE were impacted by the density of building along the shoreline, a measure of development. Impervious surface area was < 4.5% and was not consistently related to fish assemblage measures.