New footage of a dolphin hunting and eating an unusual prey — venomous sea snakes — has been captured in waters off the United States' west coast.
The dolphin was on a Navy training exercise in the Pacific Ocean, and had a waterproof camera strapped to it, when it targeted the snakes.
The Navy was training the dolphin to detect underwater mines.
Although there are previous reports of dolphins catching and interacting with sea snakes, the researchers think it's the first time a dolphin has been observed eating them.
Dolphins typically prey on fish, squid and some crustaceans.
The yellow-bellied sea snake (Hydrophis platurus) is highly venomous and may also be toxic to ingest, according to the Australian Museum.
The videos and images were captured during a study looking into the feeding behaviours of common bottlenose dolphins, published on Thursday in the journal PLOS.
To get their observations, the researchers fitted six captive dolphins with underwater cameras, and filmed them while the mammals swam in the San Diego Bay and open waters of the Pacific Ocean.
The study's lead author, Sam Ridgway from the National Marine Mammal Foundation (NMMF) and the University of California, has since died.
But it was noted in the paper that the dolphin didn't appear to suffer any ill effects from consuming the snakes.
A single dolphin ate a total of eight small snakes, while one larger sea snake, "probably an adult", escaped.
"Our dolphin displayed no signs of illness after consuming the small snakes," the researchers stated in the paper.
"Our observations, together with the earlier observations [of playing with snakes] in wild dolphins, suggests that sea snakes [especially newborns] could at times be prey for dolphins."
While the video footage (below) only shows the sea snake before it was captured, the researchers said the head shaking and audible squeal of the dolphin coincided with it killing and eating the snake.
Researchers contacted by the ABC, including the co-founder of the Shark Bay Dolphin Research project in Western Australia, Richard Connor, paid tribute to the huge contribution Sam Ridgway made to dolphin research.
"The diversity of Sam Ridgway's contributions to our understanding of dolphin physiology, anatomy and behaviour is astonishing and unmatched," said Professor Connor from the University of Massachusetts, who wasn't involved with the research.
Of the six dolphins used in the study, two were filmed while swimming in a seawater pool, two in the San Diego Bay, and two on the Navy training exercise.
Dolphins are 'basically arseholes'
Simon Allen, a senior lecturer at the University of Bristol and Adjunct Research Fellow at the University of Western Australia, said the study, especially given the perspective of cameras mounted on the dolphins, made for some "pretty cool observations and findings".
Dr Allen, who is also a principle investigator with Shark Bay Dolphin Research, said bottlenose dolphins were renowned for being exploratory and "playing with" all sorts of animals.
"Bottlenose dolphins are famously innovative — they try new things. If you'll forgive my language, they're basically arseholes, they pick on other animals, they're sort of the street gangs," he said.
"On Moreton Island, they've brought all sorts of interesting things in to where they're being handfed, like bringing in a moray eel or chasing a turtle for shits and giggles.
"Sometimes they mouth pufferfish until they expand into an inflated ball — then they'll play with that."
But while playing with animals is one thing, Dr Allen, who wasn't associated with the study, said it was unusual for a dolphin to eat something like a sea snake.
He said that animals might grab unusual food when resources were scarce or if an animal was under environmental stress.
"When times are a bit tough, like when there's been a change in environmental conditions or a marine heatwave, then we see a spike in them targeting things they normally wouldn't," he said.
As the dolphin in question was born in captivity, the study's authors suggested that inexperience in hunting could have been a factor.
"Perhaps the dolphin's lack of experience in feeding with dolphin groups in the wild led to the consumption of this outlier prey," they wrote.
As well as eating sea snakes, the dolphins were frequently recorded creating suction with their mouths to draw in prey, rather than simply clamping down on them with their teeth.
They were also seen creating a vacuum when reorienting fish in their mouths for easier swallowing.
In this case the lips were flared, and the gular region, or throat, was expanded to create negative pressure to prevent the fish escaping.
Professor Connor has done some work with underwater cameras in the past — though never attached to dolphins.
He said this study was an important contribution to our knowledge of bottlenose dolphins.
"Our cameras never granted us the remarkable perspective shown in this paper that enabled the authors to infer ingestion by suction.
"This is therefore an important contribution, and one that will likely spur our research team and others to further investigate dolphin feeding behaviour in the wild using simultaneous video and acoustic recording."
