The secret to dolphins’ swimming speeds

February 6, 2014

UC Santa Cruz gets a cool mention in a Discovery piece that examines a new research paper on the speeds at which dolphins swim.

The “Acknowledgements” section of a scientific paper is usually a good cure for insomnia—just a list of names of collaborating scientists and funding agencies. So what is the U.S. National Swim Team doing in the acknowledgements of a new paper on dolphins?

Turns out our swim team held the answer to one of marine biology’s oldest conundrums—how dolphins swim so fast with limited muscle power.

Frank E. Fish (yes, for real,) a marine biologist at West Chester University, had been searching for a way to directly measure the thrust — i.e. the power – of a swimming dolphin. Dolphins propel themselves forward by moving their tails with their lateral flukes, while using their flippers to steer. The flukes push on the water around them, and the water pushes back to create thrust. Naturally, Fish headed to UCSC for help with his research.

Fish darted for UC Santa Cruz, where his buddy Terrie Williams had two bottlenose dolphins, Primo and Puka, that could serve as test subjects.

The team bought a soaker hose, in which water seeps out of several tiny pores, and placed it at the bottom of a pool. They pumped compressed air through the hose, creating a curtain of tiny bubbles. Trainers then directed Primo and Puka to swim through the curtain while a video camera taped the location and movement of the bubbles. From there, it was simple to calculate the thrust exerted by the dolphins’ flukes.

Although they reached a speed of only 8.3 mph, the dolphins exerted 5.4 kilowatts of power, more than enough to explain their top swimming speed without invoking any hydrodynamic Houdini (and that top speed of 22.4 mph studied by Gray may have been a specious observation after all, as Fish said the dolphin may have been riding the boat’s bow wave rather than moving on its own).

Thus Fish’s findings indicate that Gray’s paradox is no paradox after all, as dolphins have sufficient power and musculature to explain their speed. This is in line with other work by Tom Lang, a former Navy researcher, that came to similar conclusions.

Now that that’s done, however, Fish is thinking bigger.

With this technique, “we’re not limited by size,” Fish said. “Why not try to do it on a whale?”

You can read his study online at the Journal of Experimental Biology. 

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