MEPS 324:261-270 (2006)  -  doi:10.3354/meps324261

Convergence or divergence: where do short-tailed shearwaters forage in the Southern Ocean?

Eric J. Woehler1,2,*, Ben Raymond2, David J. Watts2

1Institute of Antarctic and Southern Ocean Studies, University of Tasmania, Private Bag 77, Hobart 7001, Tasmania, Australia
2Australian Antarctic Division, Department of the Environment and Heritage, Channel Highway, Kingston 7050, Tasmania, Australia

ABSTRACT: Short-tailed shearwaters Puffinus tenuirostris (STSH) make use of a number of physical oceanographic features on their foraging trips to the Southern Ocean from their breeding colonies in southeast Australia. We examined the patterns in STSH at sea in the southern Indian Ocean with respect to various physical oceanographic features. Between mid-September and mid-January, there was a prominent peak in STSH densities associated with the Antarctic Polar Front (APF). A secondary peak in foraging STSH densities associated with the Antarctic Divergence (AD) was also present from late November to mid April. The high densities of STSH associated with the APF and AD support the interpretation that these features are concentrating prey in a predictable manner. As the summer breeding season progresses, STSH are observed farther southward and westward, reaching their greatest distances from their colonies at the time when they are feeding chicks. The ice edge did not appear to be a foraging focus for STSH, but represented the southern-most limit of STSH foraging in the Southern Ocean. Throughout this southward and westward movement, STSH avoid areas with pack ice. As the Marginal Ice Zone (MIZ) retreats southward, the STSH follow and, by mid summer, are foraging over the Antarctic continental shelf. The shelf break, MIZ and AD overlap spatially during the summer months as the MIZ retreats southward past the AD and over the continental shelf. The individual influences of each of these 3 oceanographic features could not be disentangled. The southward shift by STSH from the APF to the more productive MIZ/AD/continental shelf is associated with the hatching of eggs and the onset of the elevated energy demands of growing chicks.

KEY WORDS: Short-tailed shearwater · Puffinus tenuirostris · Foraging · Southern Ocean · Oceanographic features · Prey predictability

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