The dolphin begins the routine by shooing a cuttlefish out of hiding and pinning it to the sand to kill it (Image: Julian Finn et al) Next, she nudges the invertebrate off the seafloor with her snout (Image: Julian Finn et al) To remove the cuttlefish’s ink, which can slow digestion, the dolphin shakes it back and forth (Image: Julian Finn et al) Rubbing the inkless corpse against the sand breaks and releases its indigestible cuttlebone. The filleted cephalopod is now ready to eat (Image: Julian Finn et al) Advertisement The dolphin begins the routine by shooing a cuttlefish out of hiding (Image: Julian Finn et al) She proceeds to pin it to the sand to kill it (Image: Julian Finn et al) Next, she nudges the invertebrate off the seafloor with her snout (Image: Julian Finn et al) To remove the cuttlefish’s ink, which can slow digestion, the dolphin shakes it back and forth (Image: Julian Finn et al) Rubbing the inkless corpse against the sand breaks and releases its indigestible cuttlebone (Image: Julian Finn et al) The filleted cephalopod is now ready to eat (Image: Julian Finn et al)

Considering they can’t wield a knife or cleaver, dolphins make impressive butchers. Researchers in Australia recently observed a bottlenose performing a precise series of manoeuvres to kill, gut and bone a cuttlefish.

The six-step procedure gets rid of the invertebrate’s unappetising ink and hard-to-swallow cuttlebone.

See a gallery of dolphin butchery

“The behaviour seems so obviously related to making the item more palatable,” says Tom Tregenza, an evolutionary biologist at the University of Exeter, UK.

Colleague Julian Finn, a marine biologist at Museum Victoria in Melbourne, Australia, observed a single female dolphin performing the underwater move in 2003 and again in 2007. At the time, he was studying mating in cuttlefish, which breed in large swarms off the coast of South Australia.

Flushed out

The procedure begins when the dolphin shoos a cuttlefish out of an algal forest into an open patch of the seabed. Next, she pins the cuttlefish down, ramming it into the ground. To rid the body of ink, she uses her snout to pick up the cuttlefish, and then shakes it several times until a black cloud streams out.

The dolphin then grinds the cuttlefish along the sea floor to break and release its bone. “There’s an interesting cracking noise which you can hear,” says Tregenza, who has only seen the performance on video. “The cuttlefish bone pops out like a bar of soap,” and dinner is served.

Although Finn has only caught one dolphin in the act, her preference for filleted cuttlefish seems unlikely to be unique. “My guess would be that if we spent more time under water with dolphins and cuttlefish, we’d see other dolphins doing it,” Tregenza says.

Girls’ school

Another question raised by the observation is how dolphins learn this feat in the first place. Researchers have shown that female dolphins teach their offspring to wield sea sponges like a shield when they are hunting fish. One recent study showed that daughters are more eager to learn the skill than sons.

Butchery could be passed on the same way. “Is this the dolphin that invented this technique or did it learn from its mother or sister,” Tregenza wonders.

Another mystery is how the first dolphin butcher acquired its skills. Like many animals, dolphins engage in play – a behaviour that has no obvious immediate benefit. The procedure may have originated when a dolphin began knocking around a cuttlefish, Tregenza speculates. “Play is a way of trying things out, and if they work, they do them again,” he says.

Janet Mann, a behavioural ecologist at Georgetown University in Washington DC, has noticed cuttlefish bones floating in the water around her team’s bottlenose study site north of Perth, Australia.

“We didn’t know how they got them out,” she says. A similar kind of butchery is a possible, but without conclusive proof she is reluctant to jump to any conclusions. However, she has witnessed her dolphins remove spines from flathead fish and consume metre-long Golden Trevally fish in pieces.

“It could just be that Australian dolphins are smart,” she says.

Journal reference: PLoS ONE, vol 4, p e4217