Sunday, September 20, 2015

[Cetology / Behaviour • 2015] Whale Killers: Prevalence and Ecological Implications of Killer Whale Orcinus orca Predation on Humpback Whale Megaptera novaeangliae Calves off Western Australia

Figure 3. A mother humpback Megaptera novaeangliae and her calf at Ningaloo Reef, Western Australia. Although the killer whales broke off the attack when the pair moved into shallow reef waters, the damage to the calf’s lower jaw during the attack would likely prove fatal (#11).
Photo: J. Totterdell.  doi: 10.1111/mms.12182

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.

Keywords: escorts; humpback whales; killer whales; Megaptera novaeangliae; Orcinus orca; predation; scavenging; Western Australia; top-down forcing

Pitman, R. L., Totterdell, J. A., Fearnbach, H., Ballance, L. T., Durban, J. W. and Kemps, H. 2015. Whale Killers: Prevalence and Ecological Implications of Killer Whale Predation on Humpback Whale Calves off Western Australia. Mar Mam Sci. 31(2); 629–657 doi: 10.1111/mms.12182
Orcas spotted attacking and killing Humpback calves during a spate of vicious assaults (Wester…
War of the WHALES: Orcas spotted attacking Humpback cousins via @MailOnline