Humpback whales often travel alone, roaming the oceans with their haunting refrains. So, when researchers observed small groups of humpbacks seemingly working together to protect seals, they were fascinated.
In 2009, Robert Pitman and John Durban were studying killer whales in Antarctica. The two researchers, then at NOAA’s Southwest Fisheries Science Center, observed two humpbacks intervening as orcas attacked a Weddell seal stranded on an ice floe. When the seal was washed into the water, it swam towards one of the humpbacks, which rolled onto its back, sweeping the animal onto its chest.
As the killer whales approached, the humpback arched its chest out of the water, lifting the seal clear of the surface. When the seal started to slide off, the whale nudged it back into place with its flipper. Eventually, the seal escaped to a nearby ice floe.
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The incident might have been easy to dismiss, but a week earlier, the duo witnessed something similar. This time, orcas were harassing a crabeater seal when a different pair of humpbacks charged in, bellowing loudly and slapping the water with their tails and 15-foot flippers. In the fracas that followed, the killer whales swam off.
The encounters prompted Pitman and Durban to investigate whether other researchers had witnessed similar incidents. And it turned out they had.
In a 2016 review, Pitman and colleagues identified 31 cases of humpbacks mobbing killer whales that were attacking prey. Sometimes, that prey was a juvenile humpback, but more often, the orcas were hunting seals, sea lions, porpoises and other marine mammals. On one occasion, humpbacks even intervened in an attack on a pair of ocean sunfish.
So, what’s going on?
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One explanation is that the behaviour is instinctive. Humpbacks may have evolved an innate response to killer whale calls, prompting them to rush towards an attack. They may not know what species is being hunted, but a response that occasionally helps protect their own young could be worth having, even if it more often benefits other animals.
Adult humpbacks can grow up to 19 metres long and weigh up to 40,000 kilograms. Their sheer size makes them difficult targets for predators, but some bear the scars of orca attacks sustained when they were calves. Scarred adults have been seen harassing orcas, raising the possibility that they remember earlier encounters. Perhaps they’re holding a grudge.
But humpbacks are intelligent animals, capable of sophisticated thinking, decision-making and communication. Their elaborate songs and complex social lives hint at minds capable of more than simple instinctive responses.
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There may, however, be a gentler explanation. The interventions may reflect a capacity for altruism – a willingness to help others, even at personal cost.
When they wrote up their observations for the journal Natural History, Pitman and Durban concluded: “When a human protects an imperilled individual of another species, we call it compassion. If a humpback whale does so, we call it instinct. But sometimes the distinction isn’t all that clear.”
top image: An adult humpback whale launching out of the water in a full breach. Credit: Marnie Griffiths/ Getty Images.
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