EFFECTS OF AQUACULTURE ON HABITAT USE BY WINTERING SHOREBIRDS IN TOMALES BAY, CALIFORNIA

We measured abundances of wintering shorebird species simultaneously o n four control plots and two aquaculture plots from November 1989 to F ebruary 1994 on tidal flats in females Bay, California. Twelve abundan ce estimates for each plot were obtained each year. We used analysis o f covariance to model the results, controlling for the presence of roo sting gulls that may have displaced foraging shorebirds. The analysis included effects related to intraseasonal timing, annual variation, an d the presence of aquaculture. The two most abundant shorebird species in Tomales Bay, western sandpiper, Calidris maurl, and dunlin, Calidr is alpina, significantly avoided aquaculture areas. Willets, Catoptrop horos semipalmatus, however, were attracted to aquaculture plots. Four other species showed no preferences for control or aquaculture plots. Evidence of underlying (pre-existing) habitat conditions did not expl ain these results. We found no differences in species richness or Shan non diversity index between control and aquaculture areas. Our results suggest a net decrease in total shorebird use in areas developed for aquaculture.