Population dynamics and secondary production of juvenile white shrimp (Litopenaeus setiferus) along an estuarine salinity gradient

We used estimates of shrimp density, growth, mortality, and secondary production during an 84-d sampling period to compare the value of nursery habitat for juvenile white shrimp (Litopenaeus setiferus) among 3 salinity zones (intermediate, brackish, and saline zones) within Sabine Lake, an estuary of the northern Gulf of Mexico. Density, growth, mortality, and secondary production were generally higher in the saline or brackish zones and lowest in the intermediate zone. The saline and brackish zones appeared to provide the most important nursery habitat on a per- area basis, but the intermediate zone also may contribute substantially to total shrimp production; although production in the intermediate zone was modest, this zone encompasses a relatively large portion (26%) of coastal wetlands in Louisiana. The relative value of nursery areas can be dynamic; variation occurs both spatially (e.g.,within an estuary and among estuaries) and temporally (e.g., from year to year). We documented within-estuary differences (i.e., differences among salinity zones within the estuary) in the value of nursery habitat for white shrimp in Sabine Lake and expect this value, especially in the intermediate zone, to vary interannually. The dynamic nature of habitats should be considered when assessing the value of estuarine nursery areas.