In "No Limit," the French National Diving team demonstrates their remarkable skills by "free diving" to incredible depths without the aid of oxygen. One of their members, Loic Leferme, has set the world record in this sport. Another Frenchman, Andy Le Sauce, has achieved the world's longest breath-hold at seven minutes and thirty-five seconds. Of course, these world records apply only to humans. Marine mammals such as whales and dolphins are the world's true deep dive champions. How do they do it?
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Evolutionary Adaptations

The ancestors of today's marine mammals first got their feet wet some 50 million years ago. Since then, a suite of adaptive strategies has evolved to permit these air-breathing animals to submerge for long periods of time. First, marine mammals actually have more blood than their land-based relatives do. Blood accounts for about 12 percent of an elephant seal's bodyweight, compared to just 7 percent in humans. Plus, the specialized blood chemistry of marine mammals allows them to store oxygen more effectively.

When this newborn Harbor Seal grows up, it will be able to store roughly twice as much oxygen in its blood as this NOAA researcher

For example, harbor seals can store roughly twice as much oxygen per 100 milliliters of blood than humans. But even these adaptations combined can not account for the lengths of time marine mammals can spend underwater. They must have other ways of conserving oxygen.

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Photos: NOAA/Dept. of Commerce