Oyster resource zones of the Barataria and Terrebonne estuaries of Louisiana

A 1:100,000 scale map delineating the subtidal oyster resource zones within the Barataria and Terrebonne estuaries was developed. Strategies to accomp lish the task included interviews with Louisiana oystermen and stare biolog ists to develop a draft map, field sampling to document oyster (Crassostrea virginica), Dermo (Perkinsus marinus), and oyster drill (Stramonita haemas toma) abundances, use of historical salinity data to aid in map verificatio n, and public meetings to allow comment on a draft before final map prepara tion. Four oyster resource zones were delineated on the final map: a dry zo ne where subtidal oysters may be found when salinities increase, a wet zone where subtidal oysters may be found when salinities are suppressed, a wet- dry zone where subtidal oysters may be consistently found due to favorable salinities, and a high-salinity zone where natural oyster populations are p redominantly found in intertidal and shallow waters. The dry zone is largel y coincident with the brackish-marsh habitat, with some intermediate-type m arsh. The wet-dry zone is found at the interface of the brackish and saline marshes, but extends further seaward than up-estuary. The wet zone and the high salinity zones are areas of mostly open water fringed by salt marshes . The dry zone encompasses 91,775 hectares, of which 48,788 hectares are wa ter (53%). The wet zone encompasses 83,525 hectares, of which 66,958 hectar es are water (80%). The wet-dry zone encompasses 171,893 hectares, of which 104,733 hectares are water (61%). The high salinity zone encompasses 125,7 05 hectares, of which 113,369 hectares are water (90%). There is a clear tr end of increasing water habitat in the four zones over the past 30 years, a nd oysters are now cultivated on bottoms that were once marsh. The map shou ld be useful in managing the effects upon oysters of freshwater diversions into the estuaries. It provides a pre-diversion record of the location of o yster resource zones and should prove helpful in the seaward relocation of oysters leases.