These days, the US Navy’s weaponry consists of more than just massive submarines and vessels. The branch also employs bottlenose dolphins to find underwater mines and even to protect a portion of the US nuclear arsenal. The Navy is currently utilizing these dolphins to research the species’ feeding and hunting habits because it is able to.
Despite how much is known about dolphins, sound and video recordings of the animals’ hunting habits in the wild have never been made by researchers. The dolphins owned by the Navy are, well, owned by the Navy, but they have freedom of movement; according to the US Naval Undersea Museum, the dolphins reside in open water and have the option to swim away at any time, but they don’t usually do so. As a result, they are free to forage for fish, providing researchers with a rare chance to gather more information than ever before about dolphins’ hunting and feeding habits.
Six of the Navy’s dolphins had affordable, commercially accessible cameras fitted to them by researchers at the National Marine Mammal Foundation in California. In San Diego Bay, a natural port off the coast of southern California, two were seen fishing. Two more dolphins were photographed feeding in the open seas of the Pacific Ocean, while two more were observed catching live local fish in a contained seawater pool. The researchers were more interested in how the dolphins hunted than where they went hunting.
Even after the fish jumped out of the water, the dolphins’ eyes turned continuously to follow them. (This is shown in the slightly unsettling, slightly amusing collection of images above, in which a dolphin appears to be grinning back at the camera as it snares its prey.) While hunting, the critters shrieked and clicked, quieting to a buzz as they got close to their victim, and then shrieking once more as they “seized, controlled and consumed the meal.” The dolphins were observed to be able to clean their jaws of the foliage without losing control of the fish when the fish would swim through underwater vegetation.
The dolphins’ method of prey collection was perhaps the most unexpected. Their findings, which were published this week in PLOS One, state that dolphins generally suck in fish from the side with their lips opened, [lower jaw] region dilated, and tongue withdrawn to increase intraoral space and create negative pressure. Because of the powerful hyoid muscle at the base of the neck, bottlenose dolphins are ideally suited to take in fish in this fashion. Similar to how other marine animals, such as the toothed whale, feed, this involves creating an underwater vacuum that attracts fish that are very close to the animal.
The National Marine Mammal Foundation plans to do a similar study with wild dolphins in the future to compare their feeding behaviors to those of dolphins that protect and provide for humans. The group comes to the conclusion that its research would be useful to groups looking into and supporting feeding programs for endangered dolphin populations.