Aspects of the ecology of killer whale (Orcinus orca Linn.) groups in the near-shore waters of Sub-Antarctic Macquarie Island

• Published in: Polar Biology
• Main Authors: Travers, Toby, van den Hoff, John, Lea, Mary-Anne, Carlyon, Kris, Reisinger, Ryan, de Bruyn, P., Morrice, Margie
• Other Authors: Institute for Marine and Antarctic Studies Hobart (IMAS), University of Tasmania Hobart, Australia (UTAS), Australian Antarctic Division (AAD), Australian Government, Department of the Environment and Energy, Antarctic Climate and Ecosystems CRC - Australia, Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC), Department of Primary Industries Australia, Department of Primary Industries, Parks, Water and Environment, Department of Zoology South Africa, Nelson Mandela University Port Elizabeth, Centre d'Études Biologiques de Chizé - UMR 7372 (CEBC), Institut National de la Recherche Agronomique (INRA)-La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS), University of Pretoria South Africa, School of Environmental and Life Sciences - SELS (Callaghan, Australia), University of Newcastle Callaghan, Australia (UoN)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: Feeding behaviour; Diet; Southern elephant seal; Group size; [SDE]Environmental Sciences; Antarctic; New Zealand; Antarc*; Elephant Seal; Elephant Seals; Killer Whale; Macquarie Island; Mirounga leonina; Orca; Orcinus orca; Polar Biology; Southern Elephant Seal; Southern Elephant Seals; Killer whale
• Online Access: https://hal.science/hal-01851553; https://doi.org/10.1007/s00300-018-2361-y

International audience Occurrences of killer whales (Orcinus orca) in the waters surrounding Sub-Antarctic Macquarie Island have been recorded since the 1820s; however, their presence only became the focus of scientific research in the mid-1990s. The analyses of sight-ings data collected from the island between 1986 and 2015 are presented herein. The study provides evidence of a relationship between killer whale sighting probability and seasonal prey availability. Killer whales were present at the island year-round with a distinct seasonal peak in November–December, and coincident with a peak in occurrence of southern elephant seals (Mirounga leonina) due to breeding season activity, particularly the dispersal of weaned pups. Supporting this association and killer whales’ top-down influence on the survival of juvenile and adult southern elephant seals, pinnipeds accounted for 79% of prey identified, with weaned southern elephant seal pups contributing over a quarter of feeding events observed in the near-shore environment. Fur seals and penguins were also identified as prey. Killer whale groups had a median group size of three individuals, and groups of three to five individuals were most often observed feeding/milling in near-shore waters. The largest range in group sizes were observed during their peak occurrence in early summer, particularly in the number of sub-adult and female whales per group. Adult males made up 75% of single occurrences, and singletons were most often observed travelling. Overall, the ecology of killer whales at Macquarie Island was similar to that of killer whales studied at other Sub-Antarctic locations, with comparable seasonality, behaviour, diet, and group structure. Much remains to be learnt regarding the seasonal movements of whales and their diet at other times of year, their relationship to killer whales sighted in coastal Australian, New Zealand and Antarctic ecosystems, and impact on diet from commercial fisheries operations and fluctuating prey populations.