Distribution, abundance and behaviour of Buller's, Chatham Island and Salvin's Albatrosses off Chile and Peru

During 15 cruises between 1980 and 1995, we studied three species of albatross that nest in New Zealand but occur as non-breeders along the Pacific coast of South America: Buller's Thalassarche bulleri , Chatham Island T. eremita , and Salvin's Albatross T. salvini. We logged 547 h of observation, surveying 7638 km(2) of ocean surface, and recorded 86, 27, and 475 individuals, respectively, of the three species. Chatham Island and Salvin's Albatrosses occurred throughout the Humboldt Current, but habitats differed. Buller's and Salvin's Albatrosses preferred the continental slope, while Chatham Island Albatrosses frequented mostly pelagic waters. On a latitudinal basis, Salvin's Albatross distribution was skewed northward in the austral autumn and southward in spring; Chatham Island Albatross occurred southward during autumn, but was everywhere scarce in spring; and Buller's Albatross occurred almost exclusively in the south (30degreesS to 40degreesS) in both seasons. Upwelling and wind speed were positively correlated with densities of Buller's and Salvin's Albatrosses. Densities of Chatham Island Albatrosses also were positively correlated with wind speed, but they occurred further offshore in more stratified waters (with less mixing/upwelling) than did the other two. Pelagic population estimates for the Humboldt Current system, analysed using generalized additive models, peaked at 26 700 individuals for Buller's Albatross (95% confidence interval (CI) 13 100-37 100); 6790 for Chatham Island Albatross (CI 3900-11 100); and 133 100 for Salvin's Albatross (CI 82 800-183 600). Based on adult:subadult ratios observed in the study area, our best estimates for the number of wintering adults were 9100, 5800 and 114 400 birds, respectively, or 20%, 73% and 75% of the numbers estimated (44 500, 8000 and 153 300 birds) for the breeding populations at respective colonies. If we subtract from the autumn count the number of adult-plumaged birds seen in spring (assumed to be non-breeders), then respective percentages were 0%, 73% and 65%. Foraging locations and attraction by these birds to commercial fishing operations makes them susceptible to mortality as a result of the recent development of a long-line fishery on the continental slope of Chile.