Humpback Whales Are Interrupting Orca Hunts to Rescue Completely Different Species

It’s not a story anyone would have believed if it weren’t so thoroughly documented. A pod of killer whales in Antarctica is chasing a Weddell seal that’s taken refuge on a small ice floe. The orcas swim shoulder to shoulder to create a wave that washes the seal off the ice and into the water. Death looks certain. And then, without warning, a pair of humpback whales arrives. The seal, panicking, swims towards them. A wave tosses it onto the chest of the closer humpback, which is by this point rolling belly-up at the surface. The humpback arches its chest out of the water to keep the seal high and dry, above the reach of the frustrated killer whales circling below. When the seal starts to slip off, the humpback gently pushes it back onto its chest with a flipper. The seal eventually escapes onto another ice floe. The orcas, denied their meal, swim off.

The marine ecologist who watched this happen in 2009 was, on his own subsequent account, so bewildered that it took him years to work out what he’d actually seen. And what he ended up finding, once he started asking other researchers whether they’d witnessed anything similar, was that it wasn’t a one-off. It’s a pattern. And it involves species the humpbacks have no obvious reason to help.

What the researchers actually documented

According to a 2017 review paper by Dr Robert Pitman of NOAA’s Southwest Fisheries Science Center, with Volker Deecke, Christine Gabriele and eleven other co-authors from research institutions around the world, published in Marine Mammal Science under the title “Humpback whales interfering when mammal-eating killer whales attack other species: Mobbing behavior and interspecific altruism?”, the team compiled 115 documented interactions between humpback whales and killer whales over a sixty-two-year period from 1951 to 2012. The interactions came from researchers, whale-watch operators and wildlife photographers across multiple ocean basins.

The numbers, once you sit with them, don’t quite behave the way you’d expect. In 57 per cent of the interactions, the humpbacks were the ones who started it. They swam towards the killer whales, not away. Ninety-five per cent of the orcas involved were mammal-eating forms rather than fish-eating ones, meaning the humpbacks were reliably distinguishing between the two ecological populations and only intervening when the killer whales were hunting warm-blooded prey. And in the interactions where humpbacks approached killer whales that were actively attacking something, 87 per cent involved a kill or a hunt in progress.

The bit that made the paper genuinely surprising is what happened next. When the humpbacks arrived at the scene of an attack, only 11 per cent of the time was the prey another humpback. The other 89 per cent of the time, the killer whales were hunting something else entirely. A seal. A sea lion. A porpoise. A grey whale calf. A minke whale. A sunfish. Across the full data set, humpbacks were documented interfering with orca attacks on ten different species, including six kinds of pinniped, three other cetacean species, and one bony fish.

The interventions weren’t casual. Humpbacks travelled up to two kilometres to reach an ongoing attack. They approached bellowing and trumpeting. They positioned themselves between the killer whales and the prey. They tail-slashed. They struck orcas with their flippers, which on a fourteen-metre humpback are capable of doing real damage. They stayed for hours in some cases, refusing to leave until the killer whales gave up. In one incident in Monterey Bay in May 2012, described in reporting by National Geographic on the specific case, at least fourteen humpbacks converged on a group of killer whales that had killed a grey whale calf, and spent hours preventing the orcas from feeding on the carcass. One humpback stationed itself directly next to the dead calf, head pointed at it, tail slashing every time a killer whale approached.

None of this makes obvious sense.

by Kiran Journals, Space Daily | Read more:
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