Do Humpback Whales Protect Other Animals From Orcas?

What do humpbacks do when orcas attack?

When humpback whales reach an orca attack, they rarely just watch. Observers have described them:

• Rushing toward the orcas, often from a long way off, sometimes in pairs or larger groups.
• Making loud, trumpeting blows and underwater bellows.
• Slashing their tails sideways and slapping the water with their flippers and flukes.
• Pushing between the orcas and their target, or staying beside the prey animal.
• Following the orcas and continuing to harass them, sometimes for hours.

This is a form of mobbing, in which animals band together to harass a predator. Small birds do the same when they dive at a hawk or owl. A humpback’s main weapons are its size, its huge tail and its long flippers, each up to about 5 m (16 ft) long and often covered in sharp-edged barnacles.

The study of 115 encounters

In 2016, a team led by the marine ecologist Robert Pitman of NOAA published an analysis of 115 interactions between humpbacks and orcas, gathered from scientists, naturalists and whale-watch observers. The records spanned 1951 to 2012 and came from around the world, but most were from the eastern North Pacific: 42% from Monterey Bay, California, and 23% from Southeast Alaska.

The study found several clear patterns:

• Almost all the orcas involved were mammal-eaters, the kind that hunt seals and whales.
• Where it was clear who started the encounter, humpbacks approached orcas slightly more often than the other way round, 57% to 43%.
• When orcas approached humpbacks, they attacked in most cases and targeted only calves.
• When humpbacks approached orcas that were attacking, they usually harassed them, whatever the prey.
• Among the prey being attacked when humpbacks intervened, only 11% were humpbacks. The other 89% belonged to 10 other species: three kinds of whales and dolphins, six kinds of seals and sea lions, and one fish, the ocean sunfish.

In several cases, the prey escaped while the orcas were distracted, including gray whales and probably a seal. Often, though, the rescue failed: when humpbacks arrived during attacks on seals and sea lions, the prey was still killed at least 72% of the time, and the humpbacks sometimes stayed and harassed the orcas long after the kill.

Famous rescues

The most famous case happened in 2009 near the Antarctic Peninsula. A group of orcas was hunting a seal, reported as a Weddell seal, by making waves to wash it off an ice floe, as they often do. When the seal slipped into the water, a humpback rolled onto its back and the seal ended up lying on the whale’s chest, out of the orcas’ reach. When it began to slide off, the whale appeared to use its flipper to nudge it back.

Off California, especially in Monterey Bay, humpbacks regularly rush to orcas attacking gray whale calves as the gray whales migrate north in spring. Other records involve harbor seals, California sea lions, Steller sea lions, Dall’s porpoises and minke whales.

Why do humpbacks do it?

Orcas are the main natural predator of humpback calves, so humpbacks have every reason to fight them. The researchers looked at three possible explanations:

• Protecting relatives. Helping your own calf or close kin passes on shared genes. This explains defending humpback calves, but not seals or sea lions.
• Returning favors. Some animals help others that may help them later. A seal cannot repay a whale, so this does not fit either.
• A simple rule that spills over. Mammal-eating orcas usually hunt in silence but become noisy during an attack. Humpbacks may simply respond to those sounds by rushing in, without knowing what the prey is. Because the rule often saves humpback calves, it is worth following even when it sometimes “wastes” effort on other species.

The third explanation fits the evidence best. Pitman and his colleagues concluded that the help given to other species may be unintentional, but they could not rule out real altruism, meaning help given at a cost to the helper with no benefit in return.

Do orcas hunt humpback whales?

Yes, but mostly calves. A study off Western Australia found that orcas there killed humpback calves regularly during the southward migration, when mothers and newborns travel along the coast. Many adult humpbacks carry rake-like tooth scars, showing that they survived attacks when they were young.

Adults are big and powerful enough that orcas rarely try to kill them. Mothers protect their calves by keeping them close, lifting them onto their backs or heads, and being escorted by other adults, which may help explain why the anti-orca response is so strong. Learn more about the predators themselves in our profile of the orca.

Do other animals defend against orcas?

Humpbacks are unusual in going toward orcas instead of fleeing. Other whales defend themselves in different ways. Sperm whales form a tight circle with their heads together and tails pointing out, protecting calves in the middle. Gray whale mothers often flee into shallow water or kelp beds. Fast rorquals such as fin and minke whales usually try to outrun orcas.

Stories of dolphins and whales rescuing people are a separate matter and are mostly anecdotal, as explained in Do dolphins protect humans from sharks?