Exploitation of distant Antarctic waters and close neritic waters by short-tailed shearwaters breeding in South Australia

• Published in: Austral ecology 2011-06, Vol.36 (4), p.461-475
• Main Authors: EINODER, L.D, PAGE, B, GOLDSWORTHY, S.D, DE LITTLE, S.C, BRADSHAW, C.J.A
• Format: Article
• Language: English
• Subjects: Animal reproduction; area-restricted search; basins; Birds; breeding; chlorophyll; continental shelf; first-passage time; fisheries; foraging; Foraging behavior; habitat associations; Habitats; Marine; neritic; predators; Puffinus; scale; seabirds; search effort; tracking
• ISSN: 1442-9985; 1442-9993
• DOI: 10.1111/j.1442-9993.2010.02176.x

Identifying the primary foraging grounds of abundant top predators is of importance in marine management to identify areas of high biological significance, and to assess the extent of competition with fisheries. We studied the search effort and habitat selection of the highly abundant short-tailed shearwater Puffinus tenuirostris to assess the search strategies employed by this wide-ranging seabird. During the chick-rearing period 52 individuals were tracked performing 39 short foraging trips (1-2 days), and 13 long trips (11-32 days). First-passage time analysis revealed that 46% of birds performing short trips employed area-restricted searches, concentrating search effort at an average scale of 14 ± 5 km. Foraging searches were more continuous for the other 54%, who travelled faster to cover greater distances, with little evidence of area-restricted searches. The prey returned indicated that continuous searchers consumed similar prey mass, but greater prey diversity than area-restricted search birds. On long trips 23% of birds travelled 500-1000 km to neritic (continental shelf) habitats, showing weak evidence of preference for areas of higher chlorophyll a concentration, and foraged at a similar spatial scale to short trips. The other 76% performed rapid outbound flights of 1000-3600 km across oceanic habitats commuting to regions with higher chlorophyll a. The spatial scale of search effort in oceanic habitat varied widely with some performing broad-scale searches (260-560 km) followed by finer-scale nested searches (16-170 km). This study demonstrates that a range of search strategies are employed when exploiting prey across ocean basins. The trade-offs between different search strategies are discussed to identify the value of these contrasting behaviours to wide-ranging seabirds.