NOBODY EVER TOLD Gilligan the dolphin not to bite off more than he could chew.
The male Indo-Pacific bottlenose dolphin is the first known cetacean to die from asphyxiation by octopus, a new study says.
When the young male, found on a beach about two hours south of Perth, was brought to Stephens' lab for a post-mortem in August 2015, bits of a Maori octopus were still hanging out of his mouth.
Other dolphins have been observed killing and eating octopi before, so Stephens conducted a post-mortem to figure out what went wrong—particularly because the animal, nicknamed Gilligan, was in amazing condition. First, she had to remove the octopus.
"It really was a huge octopus, I just kept pulling and pulling and thought, 'My god! It's still coming,'" Stephens says, adding that it had a tentacle span of 1.3 metres.
The autopsy, described in a recent study in the journal Marine Mammal Science, revealed that the problem arose when Gilligan was swallowing what would be his last meal.
Dolphins can disengage their epiglottis—a flap of tissue that connects the larynx to the blowhole—to open up their throats and swallow larger pieces of food.
Stephens says that the 2 kilogram cephalopod appeared to have grabbed onto Gilligan's larynx with a tentacle, preventing it from reconnecting to the dolphin's breathing apparatus and effectively suffocating him to death.
"That octopus might have been, in theory, dead, but the sucker was still functional," Stephens says, adding that while nobody wins in a situation like this, "the octopus gets a bit of a last hurrah."
PHOTOGRAPH BY DR NAHIID STEPHENS, MARINE MAMMAL SCIENCE
Playing With Their Food
Kate Sprogis, a research fellow at Murdoch University, says an octopus is "not easy prey to just swallow."
While studying the dolphin population near Bunbury, where Gilligan died, Sprogis has observed dolphins tossing octopi in the air in an attempt to tenderise the invertebrates—breaking them up into smaller, more digestible pieces.
A cetacean will often breach the surface and send the octopus flying through the air—quite the spectacle, according to Sprogis, who wasn't involved in the new study.
"It's quite energetically demanding for the dolphins," she says, adding the unhappy cephalopods will try to cling to the dolphins' heads. The sheer effort required is "why we think the octopus is highly nutritious."
After throwing their prey around, the dolphin usually bites off the octopus' head—though the battle is far from over, since its arms can remain active for some time. (Related: "Why These Dolphins Behead Their Prey.")
As for Gilligan, "he obviously didn't toss it enough, and got a bit cocky and swallowed it," Sprogis says.
Learning From Tragedy
While Gilligan's unique death may have been a first as far as scientists are concerned, it likely happens more frequently in nature.
Historic seafarers told stories of sperm whales battling krakens—likely just misunderstood fights between giant octopi and sperm whales, Stephens says.
Gilligan's situation is "an interesting way of highlighting the things that happen in our backyard all the time that we're not really aware of," she says.
Not only that, but the dolphin's unfortunate end helps scientists learn more about the animals and their biology. As a young healthy male, Gilligan is also an important counterpoint to many of the sick, old biological samples that pathologists often encounter.
"These opportunities don’t come up that often," Stephens says, "so the more we can visualise these individuals after the unfortunate, tragic event of their death, the better it is."
Lead Image: Gilligan was discovered on Stratham Beach in Bunbury, Australia, with an octopus still sticking out of his mouth. PHOTOGRAPH BY JOHN SYMONS, MARINE MAMMAL SCIENCE