Whale killers: Prevalence and ecological implications of killer whale predation on humpback whale calves off Western Australia

Abstract

Reports of killer whales (Orcinus orca) preying on large whales have been relatively rare, and the ecological significance of these attacks is controversial. Here we report on numerous observations of killer whales preying on neonate humpback whales (Megaptera novaeangliae) off Western Australia (WA) based on reports we compiled and our own observations. Attacking killer whales included at least 19 individuals from three stable social groupings in a highly connected local population; 22 separate attacks with known outcomes resulted in at least 14 (64%) kills of humpback calves. We satellite-tagged an adult female killer whale and followed her group on the water for 20.3 h over six separate days. During that time, they attacked eight humpback calves, and from the seven known outcomes, at least three calves (43%) were killed. Overall, our observations suggest that humpback calves are a predictable, plentiful, and readily taken prey source for killer whales and scavenging sharks off WA for at least 5 mo/yr. Humpback "escorts" vigorously assisted mothers in protecting their calves from attacking killer whales (and a white shark, Carcharodon carcharias). This expands the purported role of escorts in humpback whale social interactions, although it is not clear how this behavior is adaptive for the escorts.

Movement and diving of killer whales ( Orcinus orca ) at a Southern Ocean archipelago

“…Photographic identification matches have revealed long-range movements (over months to years) of offshore killer whales, including minimum distances of 4,435 and 4,345 km between Alaska and California (Dahlheim et al, 2008), and of transient killer whales (minimum distance 2,660 km between Alaska and California) (Goley and Straley, 1994). An animal satellite tagged in the Canadian Arctic travelled over 5,400 km in about a month (Matthews et al, 2011), an individual in the Gulf of Alaska travelled 3,839 km in 30 days (Matkin et al, 2012), and one tagged off Western Australia moved 1,964 km in 22 days (Pitman et al, 2015). Durban and Pitman (2012), however, documented rapid, directed movements to warm, subtropical waters (20.9-24.2°C; 30-37°S) by 6 type B killer whales from the Antarctic Peninsula.…”

Intraguild predation and partial consumption of blue sharksPrionace glaucaby Cape fur sealsArctocephalus pusillus pusillus

“…In marine systems, this has previously been reported for harp seals Pagophilus groenlandicus feeding on Atlantic cod Gadus morhua (Lilly and Murphy 2004), white sharks selectively consuming blubber-rich areas of cetaceans (Fallows et al 2013) and killer whales Orcinus orca feeding on cetacean and avian prey (e.g. Pitman and Durban 2010;Pitman et al 2014). The observed partial consumption of blue sharks is consistent with this theory, given their confirmed high local density in the second instance we report and the nature of their anatomy in which energy is concentrated in their viscera (e.g.…”

Killer Whale (Orcinus orca) Predation on Beaked Whales (Mesoplodon spp.) in the Bremer Sub-Basin, Western Australia

“…Killer whales have been sporadically recorded in all state and territory waters. Higher concentrations have been reported off southern Australia, from southern New South Wales to western Victoria [25,26], and off Western Australia, from the far south-east to mid-north coast [27,28]. Seasonal trends in sightings in some locations may suggest fairly consistent occupancy that may coincide with aggregations of prey [25].…”