Humming clicks and joyful shouts of triumph provide the soundtrack to the first images of dolphins hunting freely off the coast of North America. For a scientific study published in 2022, the U.S. Navy attached cameras to dolphins trained to detect underwater mines and preserve some of America’s nuclear stockpile, then released them to hunt in San Diego Bay.
Clever marine mammals have surprised researchers by offering exciting chases and even targeting venomous sea snakes. Despite such popular, well-known animals, we still don’t know many basic things about these highly social and often rude marine mammals, such as how they generally eat.
Researchers generally know of at least two techniques: lapping the prey like noodles from a bowl and whipping it like a hot dog between trips to the state fair.
But the images showed much more.
Cameras attached to six bottlenose dolphins (Tursiops truncatusSix months of video and audio recording from the US National Marine Mammal Foundation (NMMF) has given us a new level of understanding of these mammals’ hunting strategies and communications.
Recording equipment was placed on their backs or sides, showing the disturbingly odd angles of their eyes and mouths. Although not wild, these dolphins have regular hunting opportunities in the open ocean and supplement their normal diet with frozen fish. So, as NMMF marine mammal veterinarian Sam Ridgway and colleagues explain in 2022, these animals are likely to use methods similar to their wild counterparts.
“Dolphins clicked almost continuously at intervals of 20 to 50 milliseconds while hunting,” they write in their paper.
“As the prey approaches, the click intervals shorten into a final buzz and then a squawk. “During contact with the fish, the buzzing and screaming were almost constant until the fish was swallowed.”
Camera dolphins caught more than 200 fish, including perch, grayling, flounder, finfish and pipefish. Smelt would often launch themselves into the air in desperate attempts to escape agile predators. However, the dolphins followed their every move, swimming upside down, allowing their rotating eyes to obtain a clear view; This technique has been seen before in wild dolphins.
“It turns out that these dolphins use both sight and sound to find their prey,” Ridgway and colleagues wrote. “Dolphins have always used echolocation to find fish from a distance. Near vision and echolocation were used together.”
The cameras also recorded the animals’ heart sounds as they pumped to keep up with this strenuous activity, showing that instead of striking at their prey, the dolphins used suction to help swallow still-struggling prey with their impressively strong throats. muscles
Dolphins mostly suck fish through the sides of their open mouths, their throat muscles expanding and their tongues retracted. The expanded internal oral cavity helps create the negative pressure added by the sucking muscles. While dolphins have been caught messing around with snakes before, the images, which include a river dolphin playing with an oversized anaconda, are the first to confirm they can also eat reptiles.
A dolphin ate eight highly venomous yellow-bellied sea snakes (hydrophis platurus).
“Our dolphin showed no signs of illness after eating the small snakes,” the researchers explained, but acknowledged that this might have been unusual behavior since dolphins are captive animals. “Perhaps the dolphin’s lack of experience feeding with a group of dolphins in the wild led to the consumption of this extraordinary prey.”
The study’s lead author, Sam Ridgway, died at the age of 86 shortly before the study was published, leaving behind a rich research legacy.
“His creative approach to working with Navy dolphins to better understand the species’ behavior, anatomy, health, echolocation and communication will continue to educate and inspire future scientists for generations to come,” he said. Guard NMMF ethologist Brittany Jones.
As for the Navy’s trained dolphins, the NMMF explains on its website that they “work in open water almost every day.”
“They can swim if they want to, and over the years some of them have been able to swim. But almost everyone stays.” This study was published on: PLOS ONE.
Source: Port Altele
