The original sea shepherds: Humpback whales defend ocean mammals

The high seas have a new sheriff: humpback whales who protect other ocean mammals from attack. Across the world’s oceans, humpbacks regularly defend other whales and even seals against predation by orcas, suggests a fascinating new study of a behavior witnessed dozens of times but never before analyzed. It might be instinctive; it might also be a matter of principle.

Published in the journal Marine Mammal Science, the study was led by National Marine Fisheries Service ecologist Robert Pitman, who in 2009 watched two humpbacks rescue a Weddell seal from orcas. One of the whales literally carried the beleaguered seal to safety. Intrigued by what he saw, Pitman reached out to other marine scientists, who furnished his team with no fewer than 115 examples of humpbacks fighting off orcas as they attacked other animals.

Crucially, humpbacks didn’t pick fights with just any orcas. They left fish-eating orcas alone, in all but one case targeting mammal-eating orcas. Sometimes the orcas hunted other humpbacks, but often their prey was other whale species, seals, or sea lions. Scientists call this “interspecific altruism”—helping a member of another species. The question is: Why would they do so?

For humpbacks to defend other humpbacks makes obvious sense. It could benefit their own kin, or they might expect to have the favor returned. Helping other species, though, brings no evident benefit. Pitman and his co-authors float a few possible reasons: humpbacks might be inclined to attack any orca they hear hunting, which sometimes would benefit humpbacks while providing unintended “spillover” assistance if someone else was on the menu. This might be a genetically hard-wired instinct or something taught by mother humpbacks to their children.

Given the incredible intelligence and social complexity of many whale species—some scientists have even speculated about their possessing systems of morality—one can also wonder about more nuanced layers to the humpbacks’ peacekeeping. Perhaps it reflects a code of right and wrong, with humpbacks and mammal-eating orcas engaged in a feud resembling now-historical conflicts between early human tribes.

We might not share the oceans with so many self-interested giants, but rather with creatures with moral principles and a sense of community that extends to other species. “It would be fascinating to know,” says Hal Whitehead, a Dalhousie University biologist and expert in cetacean culture who was not involved in the study.

“I think that people will start looking at these interactions a little more closely now,” says Pitman, “and we’ll have some answers to these questions.” —Brandon Keim | 10 August 2016

Source: Pitman et al. “Humpback whales interfering when mammal-eating killer whales attack other species: Mobbing behavior and interspecific altruism?” Marine Mammal Science, 2016. doi: 10.1111/mms.12343

Image: A humpback bellows at orcas attacking a crabeater seal. Credit: John W. Durban