Gray’s Paradox Solved: Dolphin Actually Have Super Strength; Don’t Need to Rely On Tricks Of Fluid Mechanics

By Ajit Jha on January 15, 2014 4:45 PM EST

Dolphin tail
Dolphins don't need any tricks of fluid mechanics to maintain their incredible speed — just super strength. (Photo: Shutterstock)

Back in the 1930s, British zoologist Sir James Gray was intrigued by dolphins' strange swimming behavior. According to his observation, dolphins could swim at the rate of 20 knots (that is, 10.3 meters/second). However, his studies had shown him that the animal didn't have muscles strong enough to accomplish this feat. He called this "Gray's Paradox," and speculated that the animal probably used some trick of fluid mechanics to sustain the performance.

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A team of scientists now claim to have solved Gray's paradox. In a study published in the Journal of Experimental Biology, a team led by Dr. Frank Fish of West Chester University, concluded that dolphins can actually exert enough power to sustain their swimming speed — no trickery needed. Fish had been grappling with the problem for long, according to a press release. He used a hydrodynamics model that looked at the motion of the dolphins' tail flukes to measure the power the animals can produce. Eventually, he came to the conclusion that dolphins can produce enormous amounts of power.

Fish then wanted to move beyond theoretical calculations to directly measure the force exerted by a dolphin while swimming in water. The question was how. He considered a method known as digital particle image velocimetry (DPIV) that can measure the force exerted by an animal while swimming in water, but concluded that that wouldn't work. "No one is going to let you put a 55 gallon drum of glass beads in with a dolphin and no one is going to let you shine a laser beam at a dolphin," Fish said.

Dr. Timothy Wei from the University of Nebraska had a solution. Wei had faced a similar problem while working with Olympic swimmers, and had successfully addressed measured their swimming power by having them swim through a curtain of microscopic bubbles. After meeting a conference, Wei and Fish teamed up along with Dr. Terrie Williams of the University of California, Santa Cruz, who agreed to let her dolphins, Primo and Puka, be subjected to the test.

The team created a curtain of bubbles in a SCUBA tank using compressed air and a garden soaker hose, then filmed the animals as they swam along the length of the bubble curtain. As the animal surged forward, the jet of water propelled backwards. The team could clearly see how the dolphin's flukes created spinning vortices. Afterward, graduate student Paul Legac and Wei calculated the amount of power produced when the animals swimming at a leisurely pace as well as when cruising at a rapid pace.

The animals produced an impressive power of 549 W when cruising leisurely at 3.4 meters/second. This is 1.4 times the amount of power that a fit amateur cyclist can sustain for an hour. However when accelerating rapidly, the animals were producing an enormous amount of power — 5400 W — an amazing figure that instantly solves Gray's Paradox. Basically, the solution is that dolphins have super strength. 

Dolphin photo courtesy of Shutterstock.

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