Despite how much we know about dolphins, researchers have never used both sound and video to capture the creatures’ hunting behaviors in a natural setting. Despite the fact that the Navy’s dolphins are, well, the Navy’s, they enjoy freedom of movement; according to the US Naval Undersea Museum, the dolphins live in open water and can choose to swim away at any point, but rarely do. This means they’re free to hunt for fish, offering researchers a unique opportunity to collect more data on dolphins’ hunting and feeding habits than ever before.
Researchers at California’s National Marine Mammal Foundation attached inexpensive, commercially available cameras to six of the Navy’s dolphins. Two were observed catching fish in San Diego Bay, a natural harbor off southern California’s coast. Two more dolphins were seen catching live native fish in an enclosed seawater pool, while another two were observed feeding in the Pacific Ocean’s open waters. It wasn’t so much where the dolphins hunted that interested the researchers, however, as it was how they hunted.
(Photo: Ridgway et al/PLOS One)
The dolphins’ eyes continuously swiveled to keep track of their prey, even when the fish jumped out of the water. (This is depicted in the slightly eerie, slightly hilarious series of photos above in which a dolphin looks like it’s smirking back at the camera as it catches its prey.) The creatures squealed and clicked while they hunted, quieting to a buzz as they approached their prey and then squealing again as they “seized, manipulated and swallowed the prey.” When a fish would swim into underwater vegetation, the dolphins were found to be capable of ridding their mouths of the vegetation without losing grip on the fish themselves.
Perhaps most surprising was the way in which the dolphins captured their prey. “Rather than seizing fish in a ‘claptrap’ of the toothy beak, dolphins appeared to mostly suck in fish from the side with lips opened, [lower jaw] area expanded, and tongue withdrawn to increase intraoral space creating negative pressure,” their research, published this week in PLOS One, reads. Bottlenose dolphins are uniquely positioned to suck in fish this way, thanks to the strong hyoid muscle that sits at the base of the throat. This is similar to how other marine mammals, including the toothed whale, feed: not by chomping, but by creating an underwater vacuum of sorts that captures fish in extremely close proximity.
The National Marine Mammal Foundation wants to follow up its study with a similar one involving wild dolphins to see if their feeding habits differ from those that protect and serve. In the meantime, the organization concludes that its research might help inform organizations studying and assisting feeding efforts in threatened dolphin populations.
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