Bottlenose dolphins living off the coast of Southwest Australia face a dilemma. The local octopuses are tasty and packed with protein, but they are also intelligent, fierce fighters. It’s not enough to bite off the heads of cephalopods, because octopuses’ nervous systems are so decentralized that their legs can continue the fight even when unleashed. Nevertheless, the dolphins have continued their hunt for tentacle meals. Now, after years of video surveillance, scientists have seen dozens of examples of dolphins’ elaborate octopus-hunting strategy.
Bottlenose dolphins are known for problem solving when it comes to hunting difficult prey. Previously, researchers have seen dolphins protect their soft snouts with sponges as they burrow into the seafloor for fish. However, octopus hunting requires different skills. First, the octopus must be disarmed – literally. And then those arms must be beaten into submission. Those who don’t learn this trick are likely to die. In an article recently published in Marine Mammal ScienceMurdoch University marine biologist Kate R. Sprogis and colleagues report encountering two dolphins killed while trying to eat octopuses:
It is clear that handling octopuses is risky behavior as a known adult male was stranded in our study area and an autopsy confirmed the cause of death was the result of suffocation by a large 2.1 kg octopus. The dolphin had tried to swallow the octopus, but the octopus was found almost intact, with the head and mantle of the octopus in the dolphin’s stomach and the 4-foot (1.3 m) arms separated from the head and out of its mouth. So is another [bottlenose dolphin] died of suspected asphyxia due to an octopus lodged in his mouth and pharynx.
Essentially, the octopuses’ tentacles continue to fight, blocking the dolphins’ airways even after most of their bodies have been swallowed. It’s a terrifying way to die, but Sprogis and the researchers note that octopuses must be such valuable prey that they’re worth it. Over seven years of observation, she and her team watched 33 dolphins “handle” octopuses in such a way that they were ready for the meal. Usually the encounter starts with the dolphin biting the head of the octopus, followed by throwing the legs in the air so that they hit the water hard over and over again. Dolphins would perform the grab-and-throw motion about 10-15 times before they were satisfied.
It’s not uncommon for dolphins to shake or swing other types of prey to break or soften them, but the process is especially important when it comes to octopuses. Dolphins must turn off defense responses in the legs to prevent the octopuses from using suction cups to attach themselves to the dolphins’ faces or throats. Basically, to kill an octopus you have to rip its head off and then kill each of its legs. Then you can party.
Dolphins are not born knowing all the ins and outs of octopus hunting. Sprogis and her colleagues found that adult females were most likely to attack octopuses, and it seemed that this was a behavior that younger dolphins learned from other members of their group. Bottlenose dolphins are very social and octopus attacks only occurred in the very largest groups. More research will be needed to know for sure how dolphins teach each other the art of octopus knockdowns, but it appears to be a strategy shared across these Australian dolphin groups. The researchers found no other reported sightings of octopus swinging in the current scientific literature.
There’s even a specific season for octopus hunting: winter and summer, when the water warms up and octopuses are well into their mating season. The dolphins may hunt octopuses more often during this time, as the cephalopods are most vulnerable then. After mating and laying eggs, octopuses age or show signs of rapid aging. They slow down and have a harder time with camouflage. It’s a perfect time for the dolphins to strike.
It’s still unclear why dolphins are willing to risk so much for such a small meal. Sprogis and colleagues mused that an octopus’s nutritional value must be “substantial.” Or, as marine biologist Holly Bik points out on Deep Sea News, maybe it’s just that “dolphins are a$$holes.”
Marine Mammal Science, 2017. DOI: 10.1111/mms.12405
Frame image by Marine Mammal Science