Environmental factors and fisheries influence the foraging patterns of a subtropical seabird, the Westland Petrel (Procellaria westlandica), in the Tasman Sea

ABSTRACT Environmental and anthropogenic influences in the marine environment are primary drivers of behavior and demographic outcomes for marine birds. We examined factors influencing the foraging patterns of the Westland Petrel (Procellaria westlandica), a highly threatened, endemic petrel that inhabits subtropical water masses primarily in the Tasman Sea, with a poorly known at-sea distribution. Risk assessments place the species at moderate risk of population impacts from fisheries-related mortality. Studies in the 1990s indicated that trawl fisheries would have an important influence on the Westland Petrel's foraging behavior. We investigated the influence of climatic conditions, marine productivity, bathymetry, the core fishery zone, concurrent fishing activity, light conditions, sex, and breeding stage on Westland Petrel foraging patterns. We analyzed the stable isotopes of carbon and nitrogen from blood sampled during the incubation period and examined changes in isotopic niche width over a 6-yr p...