Scientists think they may know why two humpback whales decided to save a struggling Weddell seal from a pod of killer whales.
According to a first-hand account written by Robert L. Pitman of the National Oceanic and Atmospheric Administration’s (NOAA’s) Southwest Fisheries Science Center in San Diego, California, and a colleague in 2009 for Natural History, their team was tracking a pod of ten killer whales near the Antartic Peninsula. At one point, the team witnessed the pod trying to knock a Weddell seal off an ice floe, presumably to eat the hapless seal.
The orcas teamed up and swam alongside each other, creating a wave that knocked the tasty-looking seal into the water — a typical hunting strategy used by killer whales.
"At one point, the predators succeeded in washing the seal off the floe," the scientists wrote. "Exposed to lethal attack in the open water, the seal swam frantically toward the humpbacks, seeming to seek shelter, perhaps not even aware that they were living animals."
(MORE: This Whale Does Something You've Never Seen Before)
Next thing they knew, one of the humpback whales rolled over, scooping up the seal onto his chest just before the killer whales reached their prey.
"Then, as the killer whales moved in closer, the humpback arched its chest, lifting the seal out of the water. The water rushing off that safe platform started to wash the seal back into the sea, but then the humpback gave the seal a gentle nudge with its flipper, back to the middle of its chest. Moments later, the seal scrambled off and swam to the safety of a nearby ice floe," wrote the scientists.
“I was shocked,” Pitman told Science magazine last week. “It looked like they were trying to protect the seal.”
(MORE: Whales Mourn Their Dead Just Like Humans Do, Study Says)
After the 2009 encounter, Pitman and his colleagues began a quest to find out if the strange behavior exhibited by the humpback whales was unusual. Pitman posted a request for information on a marine mammal listserv and received 115 descriptions of similar encounters, many from commercial whale-watching trips. He also received photos and videos of the same strange behavior.
In 31 cases of mobbing, in which the humpbacks proactively harass their predators, the whales approached orcas that were already engaged in a fight. They would chase the killer whales, often bellow, and slap their fins and tails.
“The humpbacks were definitely on the offense,” Pitman said.
Their findings, published this week in Marine Mammal Science, made a believer of Phillip Clapham, a NOAA marine biologist in Seattle, Washington, who was not involved in the research.
“They make a very good case that it’s a proactive response to killer whales,” he told Science magazine. “I think they’re absolutely right.”
Humpback whale pups often become the prey of killer whales, so the scientists weren't all that surprised that humpbacks mob their natural predator. More surprisingly, however, is the evidence that mobbing can occur when other species are under attack.
“It’s pretty mysterious,” said Trevor Branch, a fisheries scientist at the University of Washington, Seattle, who has studied populations of large whales. “We tend to think of altruism as being reciprocal, but there’s no way these other species would come back and help the humpback whales.”
(MORE: Whale Lifts Kayakers Out of Water)
On the other hand, Pitman said he and his colleagues believed the rescue may be part of their natural maternal instinct.
"It occurred to us that in all three of these encounters, the menacing behavior of the killer whales may have triggered a protective maternal response in the humpback whales," said Pitman. "Even though they did not have calves that were at risk, they acted immediately and instinctively to counter the threat posed to a smaller animal."
Pitman went on to say that "when a human protects an imperiled 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."
