Impact of black bullhead (Ameiurus melas) on turbidity in a diked wetland

Benthivorous fish in shallow, aquatic systems have been correlated with increased turbidity and declines in macrophyte production and wildlife use. Bullheads have been credited with increasing turbidity, but this has been seldom tested and has not been studied in a diked marsh. To assess the relationships of black bullhead (Ameiurus melas) and turbidity, we assembled mesocosms in the Show Pool Management Unit of The Ottawa National Wildlife Refuge, OH, U.S.A. We stocked treatment enclosures with different biomasses of black bullhead at weekly intervals. Mean turbidity within treatment enclosures was significantly higher than within controls but remained lower than that of the open marsh. Both surface and bottom turbidity increased with adult and juvenile black bullhead biomass. Turbidity increased with fine sand concentration only in the presence of juvenile fish. Wind speed and direction were significant influences on the turbidity of the open marsh, but not within control enclosures. That treatment turbidity - even at extreme biomasses - remained significantly lower than the turbidity of the open marsh implicates fetch in having a greater influence on a marsh's turbidity than the presence of black bullhead. The greater impact of benthivorous fish on turbidity within shallow systems may be an indirect one through the destruction of macrophytes and subsequent destabilization of unconsolidated substrates.