Maximizing age-0 spot export from a South Carolina estuary: An evaluation of coastal impoundment management alternatives via structured decision making

Abstract

Estuaries are among the most productive of all ecosystems and provide critical nursery habitat for many young of-the-year (age-0) marine fish. Along the South Carolina coast, former rice field impoundments in some estuarine areas are now managed to provide habitat for waterfowl. Marine fish that enter these structures during water level manipulation become trapped and suffer high mortality rates. Because these fish cannot emigrate back to coastal waters to complete their life cycles, these impoundments appear to act as sinks for marine-transient species. Our goal was to identify which of a set of management options would maximize export of age-0 spot Leiostomus xanthurus from the Combahee River, South Carolina, to the coastal population. We used a structured decision making approach to evaluate four decision alternatives: to maintain status quo, to close all impoundments while age-0 spot are most abundant in the river, to change the water level manipulation strategy to improve fish passage from impoundments, or to breach all impoundments. We also wanted to evaluate how impoundments and natural mortality influence the export of age-0 spot. The optimal management decision was to change the water level manipulation strategy to increase fish passage from the impoundments. Spot export was most sensitive to juvenile settlement in the estuary and natural mortality. The results of this model can be used adaptively for impoundment management along the Combahee River and can be modified for other estuarine areas or other fish species. © American Fisheries Society 2012.