(ORDO NEWS) — Clicks and joyful squeals of victory make up the soundtrack of our first-ever shots taken from the perspective of dolphins free-roaming off the coast of North America.
The US Navy attached cameras to its dolphins, which are trained to help detect underwater mines and protect some of America’s nuclear stockpiles, and then gave them the freedom to hunt in San Diego Bay.
The smart marine mammals did not disappoint, staging spectacular chases and even attacking venomous sea snakes, to the surprise of the researchers.
For such popular and famous animals, we don’t yet know many basic things about these highly social and often rude cetaceans, such as exactly how they usually eat.
Researchers know of at least two ways: swallowing prey like bowl noodles, and swallowing it like a hot dog between rides at the fair.
But the footage showed much more.
Cameras attached to six National Marine Mammal Foundation (NMMF) bottlenose dolphins (Tursiops truncatus) recorded six months of video and audio footage, giving us new insights into the mammals’ hunting and communication strategies.
Recording equipment was placed on the dolphins’ backs or sides, allowing them to see their eyes and mouths at unusual angles.
Although these dolphins are not wild, they are regularly given the opportunity to hunt in the open ocean, supplementing their normal diet with frozen fish.
Therefore, it is likely that these animals use methods similar to their wild counterparts, explain NMMF marine mammal veterinarian Sam Ridgway and colleagues.
“When the dolphins were hunting, they clicked almost constantly at intervals of 20-50 milliseconds,” they write.
“When approaching the prey, the intervals between clicks shortened to a final sound and then to a screech. Upon contact with the fish, the clicking and squealing was almost constant until the fish was swallowed.”
Camera-tethered dolphins caught over 200 fish, including bass, mallard, halibut, smelt and trumpeter. Smelt often threw itself into the air in desperate attempts to escape from agile predators.
But the dolphins tracked their every move, swimming upside down so their rolling eyes had a clear view, a move also seen before in wild dolphins.
“These dolphins appear to have used both sight and sound to find prey,” write Ridgway and colleagues. “At a distance, dolphins have always used echolocation to find fish. Up close, vision and echolocation have been used together.”
Cameras also recorded the animals’ heartbeats as they thrashed hard to cope with the strenuous work and showed that instead of ramming their prey, the dolphins used suction to gulp down still-resisting prey with impressively strong throat muscles.
The dolphins sucked fish mainly from the sides of their open mouth, while the muscles of the throat were tense, and the tongue was stuck out. The expanded interior of the mouth helps create negative pressure, which is reinforced by the suction muscles.
Although dolphins have been caught playing with snakes before, including river dolphins playing with an absurdly large anaconda, this footage has confirmed for the first time that they can eat these reptiles as well.
One 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 write, but they acknowledge that this may be unusual behavior as the dolphins are kept in captivity.
“Perhaps the dolphin’s lack of feeding experience with groups of dolphins in the wild led to the consumption of this unusual prey.”
The study’s lead author, Sam Ridgway, recently passed away at the age of 86, leaving behind a rich research legacy.
“His creative approach to partnering with sea dolphins to better understand the behavior, anatomy, health, sonar and communication of this species will continue to educate and inspire future scientists for generations to come,” NMMF ethologist Brittany Jones told The Guardian.
As for naval-trained dolphins, they “work in open water almost every day,” the NMMF explains on its website. “They can sail away if they want to, and over the years some of them do. But almost all of them stay.”
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