Refuting Gray’s paradox that dolphins do not have sufficient muscle power for obtaining high speeds and accelerations and must use a trick of fluid mechanics, researchers have found that dolphins are in reality stronger than the fittest human athletes.
60 years later after British zoologist Sir James Gray formulated the paradox, Frank Fish from West Chester University, USA, got his teeth into the puzzling problem.
Fish recalled that he wanted to see how much power a dolphin can produce, so he used some hydrodynamics models that looked at the motion of the flukes and came up with the realisation that dolphins could produce very high amounts of power.
But these were only theoretical calculations and to really sound the paradox’s death knell Fish would have to measure directly the force exerted by the animal on water and, although there is a method, known as digital particle image velocimetry, to visualise eddies in the water in order to measure the forces exerted by fish, it wasn’t clear how the same approach could be used on dolphins.
That was until Fish met Timothy Wei, from the University of Nebraska, USA, at a conference. Wei had encountered the same technical problems when working with Olympic swimmers, but he had got round it by asking the Olympians to swim through a curtain of microscopic bubbles.
Fish contacted his long-time friend Terrie Williams and asked if he could test the method on her dolphins, Primo and Puka.
Arriving at the University of California at Santa Cruz with a SCUBA tank of compressed air and a garden soaker hose to produce the curtain of bubbles, Fish teamed up with Wei, graduate student Paul Legac and Williams to put the dolphins through their paces.
Filming the animals as they swam along the length of the bubble curtain, the team could clearly see the vortices set spinning by the dolphins’ flukes demarcating the powerful jet of water propelled backwards as the animals surged forward.
And when Legac and Wei calculated the amount of power produced by the animals as they cruised at a leisurely 3.4 m/s, the animals were producing an impressive 549 W – approximately 1.4 times the power that a fit amateur cyclist can sustain flat out for an hour – rocketing to an eye-watering 5400 W when accelerating rapidly.
So, the dolphins did have enough muscle to power their impressive swimming performance because they are simply stronger than humans.
The study is published in the Journal of Experimental Biology.