How Do Dolphins Hunt?  A research project provides a view of a dolphin’s eye

How Do Dolphins Hunt? A research project provides a view of a dolphin’s eye

Scientists trying to understand the hunting behaviors of bottlenose dolphins have found a unique solution: docking them with video cameras.

The result is the most remarkable view of the dolphin hunting process seen so far, showing crucial details of their hunt for prey – and recording their cries of victory when they catch some.

A dolphin is seen hunting and eating various venomous sea snakes, a surprising and dangerous choice for a meal that scientists cannot fully explain.

The videos, released on Wednesday, are an “incredible addition” to the scientific knowledge of dolphin hunting in the open ocean, said biologist Brittany Jones of the National Marine Mammal Foundation, a nonprofit group based in San Diego, for email. The scientists observed “eye movements, capture strategies and movements of the lips, tongue, muscles and gular. [lower jaw] region during prey capture events that would be very difficult to achieve with wild dolphins.”

Jones worked closely with the authors of a research paper based on the video published in the journal PLOS One. The main author is Dr. Sam Ridgway, former president of the foundation and a renowned veterinarian and marine mammal scientist who died in July.

Under Ridgway, the foundation has partnered with the US Navy on its Marine Mammal Program, which trains bottlenose dolphins and California sea lions as underwater “guard dogs” to detect explosives and other objects in ports and at sea. About 70 dolphins and 30 sea lions are in the program, which is also based in San Diego, and the partnership has yielded more than 1,200 scientific studies on their physiology and behavior.

Dolphin hunting (Ridgway et al., 2022, PLOS ONE, CC-BY 4.0)

Dolphin hunting (Ridgway et al., 2022, PLOS ONE, CC-BY 4.0)

For the latest study, researchers equipped six US Navy dolphins — identified in the study only as B, K, S, Y, T and Z — with a harness and an underwater video camera that could record their eyes and mouths. The cameras also made audio recordings of any noises.

Study co-author Dianna Samuelson Dibble, a biologist at the foundation, said the video and audio give scientists unique insight into dolphin hunting behavior. While the dolphins in the study are not wild, they do have frequent opportunities to hunt in the open ocean, and scientists expect wild dolphins to hunt in the same way.

Of special note are the sounds they make while hunting. The dolphins made “clicks” every 20 to 50 milliseconds as they searched for prey, a rapid noise that only they can clearly hear and that appears to be a form of echolocation – the natural sonar sense used by dolphins, porpoises and toothed whales to detect fish. bouncing sounds out of them.

“It became apparent during video analysis when the dolphins identified the next prey target,” Dibble said in an email. “The background noise would quickly intensify, masking the sounds of many dolphins as the animal gained speed in its pursuit.”

The dolphins then began to hum as they approached, followed by a cry of victory as they caught their prey. “The buzzing and squealing was almost constant even after the fish was swallowed,” she said.

Dolphin hunting (Ridgway et al., 2022, PLOS ONE, CC-BY 4.0)

Dolphin hunting (Ridgway et al., 2022, PLOS ONE, CC-BY 4.0)

Videos show that dolphins also use their eyes to track prey up close.

“As the dolphins approached the prey, it was evident that the visible eye was oriented towards the fish,” Dibble said. “Sometimes we see a ring of skin deformation around the eyeball that is likely indicative of eye muscle contractions.”

Fish near the surface would sometimes leap into the air in a desperate attempt to escape, but the dolphins managed to stay on target. “The dolphin swam ventrally [almost upright] while visually tracking the prey and catching the fish as it returns to the water,” she said.

One intrepid animal, the Z dolphin, was seen on video hunting and devouring eight yellow-bellied sea snakes in one day, apparently suffering no ill effects, although they are known to be extremely venomous and have made other marine mammals vomit. The researchers think the snakes were juveniles that did not develop strong venom and that wild dolphins can be taught by other members of their group to avoid them.

Richard Connor, professor emeritus of biology at the University of Massachusetts at Dartmouth and director of the Dolphin Decade research project, said his research team used to use handheld cameras from boats and aerial drone video to record dolphin behavior, but not surveillance cameras. video. carried by the dolphins themselves.

“Our cameras never gave us the remarkable perspective shown in this paper,” he said in an email, adding that it would spur his team and others to investigate how wild dolphins feed with simultaneous video and acoustic recordings.

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