Photograph by Stuart Westmorland, Corbis
PUBLISHED JANUARY 15, 2014
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.
Bubbles + Lasers = A Solution
Part of the problem was that researchers weren't able to directly measure the forces dolphins produce as they move through the water.
Obtaining that kind of data requires scientists to seed the water with visible particles, such as the tiny glass beads that are used in engineering experiments, explained Fish. Those beads are then illuminated with a sheet of laser light.
By filming how the illuminated beads move in reaction to an object moving through the water, experts can determine the forces generated.
But you can't do this with a dolphin. Since it could injure the animal, "no one's going to let you put little glass beads into a tank with a dolphin," said Fish. And researchers certainly can't shine potentially harmful laser beams at the mammals.
Wei had devised a bubble curtain to stand in place of the illuminated glass beads so that he could determine forces generated by human swimmers.
So Fish and colleagues created a bubble curtain at the University of California, Santa Cruz (UCSC), where they performed experiments with two captive bottlenose dolphins.
"Dolphins tend to be afraid of everything the first time they see something," said study co-author Terrie Williams, a marine biologist who works with the animals at UCSC.
One of the dolphins seemed a little more skeptical of the bubble curtain than the other, but with some coaxing from trainers, the marine mammals soon got used to it.
"Once [the dolphins] got a feel for [the bubbles] on their skin, we were home free," said Williams.
The results showed that a dolphin's tail, or fluke, is more than capable of producing enough thrust to speed the mammal through the water. (Also see "DNA Discovery Reveals Surprising Dolphin Origins.")
"The flukes are essentially wings," said Fish. "[They] generate a lift force that is directed forward, on both the upstroke and downstroke." This produces the thrust that pushes the dolphin through the water.
The flukes are also flexible, which is key to enabling the dolphin to maintain a highly efficient way of swimming over a broad range of speeds.
"The dolphin may have the ability to control that flexibility," Fish explained. It could be that the fluke becomes stiffer the faster the dolphin swims, increasing its swimming efficiency at high speeds.
Or maybe the dolphins can actively control fluke stiffness by changing the tension of tendons in their tail, he said.
Fish isn't sure how they're doing it, but the marine biologist and colleagues are in the midst of trying to figure that out.
Either way, "we can abolish Gray's paradox," he said.
Follow Jane J. Lee on Twitter.
I am just a dumb old country boy ,that scuba dives and I and most people with common sense had know that after seeing dolphins swim.
I do wish them good luck finding out just how it works,how the dolphin controls the fluke .
Good luck. they are wonderful creatures and I think man can learn a lot from them
the wonders of our world will never cease to amaze me, even at my age (70). it is a crime
.what big oil and corps. like them are doing to destroy it. as long as the affairs of man are controlled by finance and not wisdom, the end result can only be destruction. jerry night owl, native American indian
Truly incredible creatures. In perfect command of their environment. When i was swimming with them in the Indian Ocean they swam in front at just such a speed that I could keep up but not actually catch up! See my photo here http://s36.photobucket.com/editor?image=http%3A//i36.photobucket.com/albums/e10/TariqHossenbux/dolphinstamerin_zps72369168.jpg&detailUrl=http://s36.photobucket.com/user/TariqHossenbux/media/dolphinstamerin_zps72369168.jpg.html?filters[media_type]=image&sort=3&o=1
I can't help but wonder if "Fish" ever considered the overall shape of the dolphin as it's back makes me think of a "compound bow" which would provide thrust. I find it's never really just one thing.
"Now he has the answer: Bottlenose dolphins can produce the power they need to swim ...by using their powerful tails, new experiments show."
I suspect that this article missed several key points and it may not be Mr Fish's fault. It sounds like the author of the article may have taken some shortcuts in her research on this one.
It is possible that a standing wave or fine vibration is generated by the rostrum that proceeds down the body faster than the water flwoing past the body. I have observed this several times. A wave propagating through fat beneather the skin in this manner makes a negative coefficeint of friction ie the vibrating skin also propeles the body forward.
John and Gwendolyn, the research solved Gray's Paradox by showing that the flukes provide lift on both up and down strokes...This is new! this is the answer! but they posit that the dolphins can alter the flexibility of the fluke, which allows the dolphin to maintain efficiency in various situations. How they do this is the mystery here. That is the next step. But this does not detract from the fact that they figured out how dolphins can actually swim as fast as they do. this is kinda cool stuff....
John and Gwendolyn, the research solved Gray's Paradox by showing that the flukes provide lift on both up and down strokes...This is new! this is the answer! but they posit that the dolphins can alter the flexibility of the fluke, which allows the dolphin to maintain efficiency in various situations. How they do this is the next mystery here, the next step. But this does not detract from the fact that they figured out how dolphins can actually swim as fast as they do. this is kinda cool stuff....
Yes, John Franson, I have been caught by headline headlights many times only to have them snare me into mental immobility.
"Researchers have finally figured out how dolphins swim as fast they do."
"Fish isn't sure how they're doing it, but the marine biologist and colleagues are in the midst of trying to figure that out."
Thanks for making me read to the end of the article to learn the headline was lying.
@jerry dearing thank you Jerry. you and I are the same age and I agree with you. also as big oil and big corps.can keep prices high and not use the wisdom that comes with it we can only see destruction.
With cheap energy where people could keep warm and move around more freely and use the wisdom we learn ,there would always be new ways to make there money but also make the world a better place ..
How to Feed Our Growing Planet
National Geographic explores how we can feed the growing population without overwhelming the planet in our food series.
The Innovators Project
Three decades ago, the innovative physicist had a eureka moment that explained the universe.
Latest News Video
A modern crew learns the secrets of sailing a restored New England whaling ship.