Bottlenose dolphins leap from the water in the Caribbean Sea.
Photograph by Stuart Westmorland, Corbis
Believe it or not, how dolphins can swim so fast has been something of a riddle for researchers since the 1930s.
But a new study has laid to rest one of the most vexing questions plaguing scientists about dolphin speed: How can their muscles produce enough thrust for such high speeds? “It’s been controversial for a while,” said Frank Fish, a marine biologist at West Chester University in Pennsylvania.
Now he has the answer: Bottlenose dolphins can produce the power they need to swim circles around whatever they wish by using their powerful tails, new experiments show.
The paradox began in 1936 with a British researcher named Sir James Gray, who conducted the first study on dolphin swimming, said Fish, a co-author of the study published online January 15 in the Journal of Experimental Biology.
Gray had observed a dolphin swimming around a ship at 33 feet (10 meters) per second for seven seconds, and wondered how the animal could move so quickly. (See National Geographic’s videos of dolphins and porpoises.)
Physics theory states that for something the size of a dolphin—and for the speed with which it travels through the ocean—water flow over the animal should be turbulent rather than smooth, Fish said.
That turbulent flow creates a lot more drag that needs to be overcome than smooth flow does. But when Gray input his variables into his equations and assumed a turbulent flow, “he found the animal didn’t have enough muscle mass to produce the power it needed to swim at that speed,” said Fish.”This became Gray’s paradox,” Fish said—sparking a decades-long search for an explanation of how dolphins powered through the water.
Gray assumed that the dolphin must have been doing something to turn the turbulent flow over its body into a smooth flow. But scientists hadn’t been able to figure out how the mammals did it.