Randy Clark, John Christensen, and Mark Monaco  (NOS, Silver Spring, MD), Thomas Minello, Philip Caldwell, and Geoffrey Matthews (NMFS Galveston, TX).

The Magnuson-Stevens Fishery Conservation and Management Act requires the identification of Essential Fish Habitat (EFH) for Federally managed fishery species in our Nation's marine and estuarine environments. An analysis of nekton density data in Galveston Bay, Texas is being conducted to quantitatively isolate patterns of habitat selection that could subsequently be defined as EFH. Results of this analysis will be coupled with a geographical information system (GIS) to provide a spatial mosaic of potential EFH. 

Spatial distribution map of predicted Spring densities for brown shrimp, F. aztecus, in Galveston Bay, Texas.

Nekton densities from 3,864 drop samples taken over a 16 year period in Galveston Bay were analyzed to evaluate habitat selection among Spartina alterniflora marsh edge (ME), submerged aquatic vegetation (SAV), and shallow non-vegetated bottom (SNB) by brown shrimp, Farfantepenaeus aztecus, white shrimp, Litopenaeus setiferus, and pinfish, Lagodon rhomboides. Pinfish, although not federally managed, were used in the analysis because of their high abundance in these habitats. In addition to habitat type, seasonal temperature and salinity gradients are included in the analysis to explore the extent to which deterministic and/or stochastic factors influence habitat selection. Multiple regression and multiple logistic regression techniques are being used to develop predictive models based on these continuous and classified data. Prediction formulae are then applied to habitat geographies in the GIS. As such, resultant density estimates provided a measure of habitat selection, and consequently, a spatial assessment of potential EFH. Model results will be extrapolated to other bay systems in Texas where density data are available in order to check the model reliability and robustness.