When researchers working off the coast of California decided to strap video cameras onto trained dolphins to better understand how the animals hunt and eat fish, they weren’t expecting to capture footage of one of them sucking up venomous sea snakes like pieces of floating linguine.

Underwater footage shows a dolphin catching sea snakes in the Pacific Ocean. Credit: Ridgway et al., 2022, PLOS ONE, CC-BY 4.0

It was the most unexpected finding from a recent study which captured the first video and sound of bottlenose dolphins feeding on live fish. Footage from the study shows that the mammals appear to suck down their prey by expanding their throats and flaring their lips rather than simply charging at the fish (or snakes) as previously thought. The research also sheds light on the chorus of squeals, clicks and buzzes produced by the animals during and after hunting.

"They clicked almost constantly at intervals of 20 to 50 milliseconds," Dianna Samuelson Dibble, a researcher at San Diego's National Marine Mammal Foundation (NMMF) and a member of the study team told The Guardian. "On approaching prey, click intervals shortened into a terminal buzz and then a squeal. On contact with fish, buzzing and squealing was almost constant until after the fish was swallowed."

The six dolphins used for the research are highly skilled mine-detectors deployed and trained by the US Navy to make the ocean safer for naval ships and other vessels. The animals swim in the open ocean every day and their ability to locate, communicate, and mark mines on the seafloor is incredibly accurate and effective (although some animal activists challenge the ethics of using dolphins for service – this deep dive from Hakai Magazine is worth a read if you're looking for more context). The researchers believe that the captive animals are the perfect candidates for a study focused on gleaning insights into the underwater hunting and eating behaviour of these much-loved sea mammals.

"These findings are an incredible addition to the literature providing detailed analyses during prey capture in the open ocean, which would be very difficult to achieve with wild dolphins," Dr Brittany Jones, a scientist at NMMF, told The Guardian.

Video of dolphin capturing fish in San Diego Bay. Credit: Ridgway et al., 2022, PLOS ONE, CC-BY 4.0

The mesmerizing GoPro footage offers a close-up glimpse of dolphins hunting and eating live fish, all the while making a series of clicking and squealing sounds. The most fascinating capture is that of dolphins consuming yellow-bellied sea snakes, a behaviour that came as a surprise to the research team. Dolphins had previously been observed chasing after sea snakes but never actually eating them. Yellow-bellied sea snakes are venomous and can be dangerous if the venom is absorbed through bites or open wounds.

Despite the potential risk, one dolphin was observed slurping up eight snakes. Scientists reported to The Guardian, "The dolphin clicked as it approached the snake and then sucked it in with a bit more head jerking as the flopping snake tail disappeared and the dolphin made a long squeal." The slithering snacks didn’t appear to have any effect on the dolphin but it's unclear if sea snakes form a regular part of the diet of wild dolphins. The fact that the Navy dolphins have been raised in captivity needs to be taken into account while pondering the dolphin’s choice in food, the researchers explained.