Abundance and distribution of juvenile white shrimp Litopenaeus setiferus within a tidal marsh landscape

We measured variation in low-tide abundance of juvenile white shrimp Litopenaeus setiferus in subtidal creek channels relative to the amount of intertidal drainage area and creek edge in an adjacent tidal marsh. Samples were collected over a 2 yr period (1998 and 1999) and included 201384 individual shrimp taken by cast net during July to November from 4 different tidal creek subsystems in the Sapelo Island National Estuarine Research Reserve on the coast of Georgia (USA). Total drainage areas of the sub-systems ranged from 0.59 to 1.19 km(2). Variation in intertidal and subtidal areas, and creek edge (interface between the vegetated marsh and open water) within the upper, middle and lower reaches of each sub-system was measured from high-resolution scaled (1:16 000) aerial photographs. Shrimp were most abundant and smaller in the upper reaches of tidal channels, where the adjacent intertidal drainage area and vegetated marsh edge were greatest. Regression analysis of shrimp abundance, measured as mean catch per unit effort, showed a strong positive relationship (p < 0.001; R-2 = 0.86) with the amount of intertidal marsh edge in associated reaches (upper, middle or lower) of the creek sub-systems. Distribution and abundance of shrimp within tidal creeks probably reflected a link between estuarine landscape structure and accessibility of resources in the vegetated marshes that support shrimp production. Among the implications for management of shrimp resources in marsh habitats, we recommend a precautionary approach in making land-use decisions that would reduce structural complexity of marsh landscapes, particularly in the upper reaches of tidal creeks where juvenile white shrimp are concentrated and complex networks of creek channels enhance access to intertidal resources within the estuarine nursery.