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

Abstract

Occurrences of killer whales (Orcinus orca) in the waters surrounding Sub-Antarctic Macquarie Island have been recorded since the 1820s, however only became the focus of scientific research in the mid-1990s. The analyses of sightings 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.

Foraging behaviour and ecology of transient killer whales within a deep submarine canyon system

“…Both juvenile and adult female elephant seals are presumably profitable prey due to their ease of capture and high energy-rich blubber, and may be an important seasonal prey species for killer whales in Monterey Bay or during periods when the whales are foraging in offshore waters [ 1 , 16 , 32 , 55 ]. The importance of elephant seals as prey for mammal-eating killer whales has been extensively studied in the southern hemisphere, with observations of whales primarily feeding on southern elephant seals ( Mirounga leonine ), while using similar predatory and feeding behaviours as we have described [ 56 – 58 ].…”

Population genomic structure of killer whales (Orcinus orca) in Australian and New Zealand waters

“…In Antarctica, there are at least five ecotypes with various specialized diets. Type A, which feeds on marine mammals and penguins, with a preference for minke whales ( Balaenoptera acutorostrata ) and southern elephant seals ( Mirounga leonina ); type B1 (pack ice killer whale), which preys primarily on ice associated seals (e.g., Weddell, Leptonychotes weddellii ; crab‐eater, Lobodon carcinophagus , and leopard seals, Hydrurga leptonyx ), and occasionally minke whales; type B2 (Gerlache killer whales), which feeds on fish or squid, and sporadically on penguins; type C, which preys on fishes (e.g., Antarctic toothfish, Dissostichus mawsoni ); and sub‐Antarctic type D, which also feeds on fish (Jefferson et al, 2015; Pitman, 2011; Pitman & Durban, 2010, 2012; Pitman & Ensor, 2003; Pitman et al, 2007; Travers et al, 2018). Some Antarctic ecotypes appear to be sympatric in range and exhibit unique diets, with parallels to the patterns observed in the eastern North Pacific ecotypes (Foote et al, 2019; Pitman & Ensor, 2003; Pitman et al, 2011).…”