Winter distribution of blue crab Callinectes sapidus in Chesapeake Bay: application and cross-validation of a two-stage generalized additive model

Abstract

We present a 2-stage generalized additive model (GAM) of the distribution of mature female blue crab Callinectes sapidus in Chesapeake Bay based on data from a fishery-independent winter dredge survey. The distribution and abundance of blue crabs was modeled as a flexible func- tion of depth, salinity, water temperature, distance from the Bay mouth, distance from submerged aquatic vegetation (SAV), and bottom slope for each of the 13 yr of data available. Depth, salinity, temperature, and distance from the Bay mouth were found to be the most important environmental determinants of mature female blue crab distributions. The response curves for these variables dis- played patterns that are consistent with laboratory and field studies of blue crab/habitat relation- ships. The generality of the habitat models was assessed using intra- and inter-annual cross-valida- tion. Although the models generally performed well in cross-validation, some years showed unique habitat relationships that were not well predicted by models from other years. Such variability may be overlooked in habitat suitability models derived from data collected over short time periods.