Dolphins in Florida have a special way of hunting: They stir up ring-shaped plumes of mud with their tails and corral fish into an ever-tightening circle. The frightened fish then jump out of the water, often into the waiting mouths of dolphins.
To date, this behavior has been observed almost exclusively in groups of bottlenose dolphins in a few parts of Florida, says Stefanie Gazda, a researcher at the University of Florida who was the first to publish an extensive study on the phenomenon back in 2005.
Now a single dolphin near St. Petersburg, Florida, has been filmed employing this hunting trick solo.
Michael McCarthy, a hobbyist filmmaker and owner of a company that makes transparent watercraft—See Through Canoe—was recently in his boat near Seminole, Florida, and noticed a local dolphin that he’d seen making mud rings before. He set up his camera shot using a special drone with a zoom lens, staying well away from the animal to avoid bothering it (as a matter of courtesy, but also law, since federal rules prohibit disturbing marine mammals).
“I haven’t seen single dolphins do it before, but I’m not surprised," says Andrew Read, a biologist at Duke University. “Clearly the overall efficiency of the technique is greater when multiple animals are involved.”
As seen in Golfo Nuevo, Argentina, dusky dolphins (Lagenorhynchus obscurus) communicate with each other to herd anchovies into balls so they are easier to catch.
In the video, the dolphin proceeds to trap part of a group of fish, likely mullet, in the ring. These fish avoid swimming through muddy water, likely because they have good eyesight and don't like entering areas with low visibility—so they jump to steer clear, Read says. This works to the dolphin’s advantage, allowing them to catch the fish in the air or in the water within the mud-net. (Related: Why male dolphin buddies ‘hold hands.’)
Gazda has studied the division of labor in groups of dolphins pursuing these activities. A related behavior, called driver-barrier feeding, involves one leader—the driver—herding the fish toward “barrier” dolphins. This also traps the fish and helps the marine mammals make a meal of the prey.
This behavior may have initially evolved from a dolphin accidentally stirring up a plume, which it realized fish would avoid, Read says. Dolphins are known to corral fish toward other barriers, such as closed inlets, to help them hunt.
“I wouldn’t be surprised if the behavior evolved from a single dolphin sorting out the benefits of a mud plume to use as a barrier to fish against, and then realizing that a circle is even better,” he adds.
McCarthy has observed about eight to ten dolphins in the St. Petersburg region employing these solo mud-rings, and says he’s witnessed one young dolphin learning the technique from its mother.
The dolphin didn't succeed in catching a fish in this attempt, McCarthy notes, but it also didn't expend much energy to do so. He estimates from his observations that the animals successfully catch prey this way about one-third of the time.