Animals

Death by Octopus Is a Grisly Dietary Hazard for Dolphins

Eating an octopus can result in a highly unpleasant death for a dolphin unless the cephalopod is well and truly dismembered or rendered inert.

Kate Sprogis/MUCRU

It’s like a case out of a marine mammal edition of Forensic Files.

A dolphin washed up dead on a beach in Western Australia. By matching its markings to a photographic database, scientists established that the male Indo-Pacific bottlenose dolphin was a member of an extensively-studied population, and that it had in fact been observed and photographed since 2007. Researchers had even given it a name: Gilligan. Reckoned to be about 20 years old, Gilligan appeared to be in excellent condition, with thick blubber and no external injuries. But as scientists packed the dolphin’s carcass in ice and transported it for an autopsy at Murdoch University, one telltale clue pointed to a likely cause of Gilligan’s demise: octopus tentacles protruding from his mouth.

The octopus in question was a Maori octopus — the largest species in Australasian waters, and the third largest in the world. Maori octopuses can weigh up to 25 pounds, with maximum arm spans of nearly 10 feet. While this one was smaller, with a total weight of 4.6 lbs. and an arm span of 52 inches, it was still a pretty sizeable prey. Too sizeable, it turned out, for Gilligan: although its head had been severed and swallowed, its “crown” of arms was intact, and therein lay the dolphin’s doom.

In addition to those protruding from its mouth, one of the lengthy tentacles extended down the dolphin’s esophagus, while suckers on the others were firmly adhered to its throat and the back of its mouth, obstructing the larynx, pharynx, and esophagus. The dolphin’s lungs were hyperinflated; they deflated once the obstructing tentacles were removed from the airway.

The official cause of death was non-drowning asphyxiation. Gilligan had choked to death on his dinner.

Adult male Tursiops aduncus (“Gilligan”) as found on the beach. | Dr. Nahiid Stephens/Murdoch University
Dr. Nahiid Stephens/Murdoch University

The problem was not just the octopus’s size but the fact that, because of the unique organization of the the animal’s nervous system, its tentacles can remain functional and responsive for over an hour after its death. In a research paper published recently in the journal Marine Mammal Science, Nahiid Stephens and her colleagues noted that the surviving tentacles would “far outlast the breath-holding capacity of any dolphin.” Gilligan, they continue, “would have been no match for the octopus’s tenacity, and it is unknown how long this individual might have struggled to free its larynx from choking before succumbing.”

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Gilligan was not the first dolphin to succumb to death by octopus, nor will he likely be the last. In 2009, a stranded dolphin was found about a hundred miles from where Gilligan was discovered, also with octopus tentacles protruding from its mouth. Though an autopsy was not conducted, the cause of death was similarly listed as non-drowning asphyxiation. Furthermore, Stephens and her co-authors write, rangers on Penguin Island in Western Australia and the staff of a nearby ecotourism company “have anecdotally reported similar octopus-related deaths in the past in both dolphins and Australian sea lions and recounted stories of having seen, in some instances when dolphins were observed holding an octopus in their mouths, the apparently live octopus reaching up towards the dolphin's blowhole.”

Which begs the question: If eating large octopuses is so risky, why do it? The simple answer, Stephens and her colleauges suggest, is that it “likely comes down to risk vs. reward — large muscular cephalopods are an excellent, concentrated source of high quality proteins, and most cephalopods tire rapidly following a period of fast swimming.

Macroctopus maorum, familiarly known as the Maori octopus. | Luis. A. Henríquez/Institute for Marine and Antarctic Studies, University of Tasmania
Kate Sprogis/MUCRU

Interestingly, the dolphin population to which Gilligan belonged — located near the Western Australian town of Bunbury — has been observed taking extra precautions to ensure that its octopus prey is safe to eat. In another paper for Marine Mammal Science, Kate Sprogis of the Murdoch University Cetacean Research Unit and her colleagues described detailed observations of dolphins from this population shaking octopus prey above water and tossing it through the air in apparent attempts to remove the head and mantle, tenderize the arms to render them inactive, and break the octopus into smaller pieces for easier consumption.

“The dolphin needs to make sure the octopus arms are completely limp before swallowing the octopus,” Sprogis explained in an email to Seeker. “The dolphin can raise its body half way out of the water and shake/toss the octopus several meters into the air forwards, and does this consecutively over and over (sometimes more than 15 times). This would be energetically exhausting because they do it so quickly. It is a sight to see them handling the octopus.”

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While these are the only dolphins known to display this behavior with octopuses, other whale and dolphin species employ similar techniques with different prey. Bottlenose dolphins shake and toss fish and break apart giant cuttlefish into manageable pieces, and orcas shake sea lions and toss stingrays and small dolphins through the air.

Sprogis does not know how often dolphins off Bunbury die because they failed to adequately prepare their octopus meal.

“If the dolphin sinks, or washes up onto the remote beaches in the study area, then we won't know the cause of death (just that the dolphin hasn't been sighted in a long time),” she said.

She and her colleagues are on the water watching the dolphins nearly every month, but although they had not seen Gilligan shaking and tossing octopuses, Sprogis said she assumed that Gilligan knew how to do so. But, in the same way that humans know how to eat and still sometimes contrive to choke on their food, so Gilligan likely simply misjudged his ability to swallow his meal.

“It’s a risky behavior with large prey,” Sprogis noted.

And sometimes, the risk doesn’t pay off.

WATCH: Understanding the Weird Anatomy of an Octopus