Comparative use of longline oysterbeds and adjacent tidal flats by waterbirds

Abstract

Commercial oyster Crassostrea spp. cultivation in intertidal habitats may degrade foraging habitat of waterbirds. Consequently, we compared species abundances, community similarity and diversity of waterbirds using longline oyster culture beds and adjacent control plots on tidal flats of Humboldt Bay, California. Abundances of most species differed significantly between treatments, with seven of 13 shorebirds Charadriiformes and three of four wading birds Ciconiiformes more abundant on longline plots. By contrast, Black-bellied Plover Pluvialis squatarola were more abundant on control plots. Marbled Godwit Limosa fedoa, Long-billed Curlew Numenius americanus and Dunlin Calidris alpina showed mixed results depending on location and Great Blue Heron Ardea herodias were more abundant only on one control plot. Community composition was similar on longline and control plots, although diversity (H′) was greater on longline plots. Varying species' responses to longline techniques may have been associated with interspecific differences in diet and foraging behaviour, and the impacts of longlines and oyster-harvesting on prey distribution. Overall, longlines did not negatively affect the foraging behaviour of most species, but the underlying causes for increased bird use may lead to impacts on other trophic levels and over a longer temporal scale.