A number of investigations have demonstrated relationships between fisheries yields and the high nutrient loads, freshwater inputs, shallow depths, large areas of tidal mixing, coastal vegetated area, surface of lagoon-estuarine systems, and resulting high primary productivities that are typical of estuaries (Deegan et al. 1986; Nixon 1988; Sanchez-Gil and Yáñez-Arancibia 1997; Yáñez-Arancibia et al. 2004).

Thus, despite the small aggregate spatial extent of estuaries (<1% of the global marine area), a fraction exceeding 50% of U.S. fishery yields have historically been derived from estuarine or estuarine-dependent species (Gunter 1967, McHugh 1967; Houde and Rutherford 1993; Vidal and Pauly 2004).

In the Gulf of Mexico the fraction is considerably higher (Houde and Rutherford 1993); estuarine-dependent species dominate in large and valuable commercial and recreational catches (e.g., gulf menhaden support the second largest U.S. fishery by weight, penaeid shrimps support the 5th largest by value, with shrimp landings alone valued at $400-500 million per year).

In contrast to some of the adverse impacts of eutrophication, nutrient loading in estuaries may lead to increased primary productivity (both water column and benthic) which can have cascading effects through estuarine trophic webs and potentially near-shore productivity.

There also is some evidence to suggest that populations of important fish species also are adversely affected by eutrophication (Polgar et al. 1985; Rose and Summers 1993), but in general the potential fisheries benefits associated with nutrient control are unquantified.

Our research will:

1. investigate how diversions may affect ecologically important nekton species; and,
2. ways management may reduce the possibility of deleterious impacts.