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INFLUENCE OF ALTERED FRESHWATER FLOWS ON EASTERN OYSTERS
FISHER, W. S. AND J. T. WINSTEAD. INFLUENCE OF ALTERED FRESHWATER FLOWS ON EASTERN OYSTERS. Presented at National Shellfisheries Association, Philadelphia, PA, April 10 - 14, 2005.
Abstract for National Shellfisheries Association
Eastern oysters Crassostrea virginica are prominent in Gulf of Mexico estuaries. Valued both commercially and ecologically, oyster populations are threatened by human activity, including dredging, harvesting, and upstream alteration of hydrologic regimes that disrupt the amount, timing and quality of freshwater inflow. Critical life-stage requirements may depend on suitable freshwater inflow, a dynamic variable that reduces salinity, introduces terrestrial materials and mixes water masses with varying physical, chemical and biological properties. Supported by Federal subsidies for agriculture and flood control, freshwater diversions occur along every major stream and river entering the Gulf of Mexico. The Mississippi River has experienced five major upstream modifications. In 1981, Louisiana began to manage upstream freshwater flows to benefit, rather than disrupt, eastern oyster populations. Results from this program are compared with published salinity requirements for different oyster life-states. Calculation of optimal (monthly) freshwater inflow for oyster seed production indicated that high fresh water inflow is especially critical to early life states of oysters. We infer that the greatest influence of freshwater inflow is on larval survival, distribution and setting and early survival of spat.