Spatial distribution of brown shrimp (Farfantepenaeus aztecus) on the northwestern Gulf of Mexico shelf:: effects of abundance and hypoxia

We used fishery-independent hydrographic and bottom trawl surveys on the northwestern Gulf of Mexico shelf from 1983-2000 to test for density dependence and effects of hypoxia (dissolved oxygen <= 2.0 mg center dot L-1) on the spatial distribution of brown shrimp (Farfantepenaeus aztecus). Spatial distribution of shrimp was positively related to abundance on the Texas shelf but negatively related to abundance on the Louisiana shelf. Density dependence was weak, however, and may have been due to factors other than density-dependent habitat selection. Males were distributed over a broader area and further offshore than were females, though differences in spatial distribution between sexes were not large (10%-15%). Large-scale hypoxia (up to 20 000 km(2)) on the Louisiana shelf occurs in regions of typically high shrimp density and results in substantial habitat loss (up to 25% of the Louisiana shelf), with shifts in distribution and associated high densities both inshore and offshore of the hypoxic region. We discuss these results in terms of the generality of density-dependent spatial distributions in marine populations and potential consequences of habitat loss and associated shifts in distribution due to low dissolved oxygen.