How do dolphins hunt? A research project provides a dolphin’s eye view

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

The result is the most remarkable picture of the dolphins’ hunting process yet seen, showing crucial details of their search for prey – and recording their squeals of victory when they catch some.

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

The videos, released Wednesday, are an “incredible addition” to the scientific knowledge of open-ocean dolphin hunting, biologist Brittany Jones of the National Marine Mammal Foundation, a San Diego-based nonprofit group, said in an email. The scientists observed “eye movements, grasping strategies, and movements of the lips, tongue, muscles, and abdomen [lower jaw] area 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 lead author is Dr. Sam Ridgway, a former president of the foundation and a renowned veterinarian and marine mammal scientist who died in July.

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

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

For the latest study, researchers fitted 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 recorded any noises.

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

Of particular importance are the sounds they make when hunting. The dolphins “clicked” every 20 to 50 milliseconds as they searched for prey, a rapid noise that only they can hear clearly and that appears to be a form of echolocation – the natural sense of sonar that dolphins, porpoises and porpoises use. toothed whales to detect fish by bouncing sounds.

“It became apparent during the video analyzes when the dolphins had located their next prey target,” Dibble said in an email. “The ambient noise would quickly increase, masking the sounds of several dolphins as the animal picked up speed in pursuit.”

The dolphins then began to make a hum as they closed in, followed by a whoop of victory when they caught their prey. “The buzzing and squealing was almost constant until the fish was swallowed,” he 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 at close range.

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

Fish near the surface sometimes jumped into the air in a desperate attempt to escape, but the dolphins managed to stay on target. “The dolphin was belly swimming [almost upright] while visually tracking the prey and captured the fish as it landed back in the water,” he said.

One intrepid animal, Z the dolphin, was seen on video hunting down and devouring eight yellow-bellied sea snakes in one day, apparently without suffering any ill effects, although they are known to be highly venomous and have caused other marine mammals to they vomit The researchers believe that the snakes were juveniles that had not developed strong venom and that the wild dolphins may have been taught by other members of their group to avoid them.

Richard Connor, professor emeritus of biology at the University of Massachusetts Dartmouth and director of the Dolphin Decade research program, said his research team often used hand-held cameras from boats and video from aerial drones to record dolphin behavior, but not video cameras that carried by the dolphins themselves.

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

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