Air Date: Week of May 7, 2004

Living on Earth’s Jennifer Chu reports on a crucial bond between a mother dolphin and her calf.

Transcript

GELLERMAN: Just ahead – new ideas in California rules spur a generation of vehicles that are greener than green. First this note on emerging science from Jennifer Chu.

[SCIENCE NOTE THEME]

CHU: The tuna-fishing industry first adopted “dolphin-friendly” fishing practices in the 1980s. Since then, the number of dolphins killed as by-catch has significantly dropped. But a corresponding recovery of the dolphin population has yet to follow, and no one knows why for sure.

A new study published this week in the Journal of Biology offers one explanation. An Israeli mathematician created a model to analyze the complicated-but-crucial bond shared between mother dolphins and their calves as they swim. Young dolphins position themselves to hitch a “free ride” in the mother’s wake in order to keep apace. In this way, they’re much like racing cyclists.

It works something like this: the wake, or “displacement” effect, creates a forward flow pattern. The calf can ride this wave with little effort. Meanwhile, the so-called Bernoulli suction effect draws the calf close to its mother’s side. Riding shotgun, up to 60 percent of the swimming work is done for the calves. They rely on this outside boost until about age three.

But fishermen can inadvertently break this mother/calf swimming bond during a tuna chase, as the mother accelerates to escape the boats. When this happens, a calf can become permanently separated from its mother and be lost. Research suggests that because of this premature separation, a significant number of young dolphins may be dying before they are able to breed.

That’s this week’s note on emerging science. I’m Jennifer Chu.

GELLERMAN: And you’re listening to NPR’s Living on Earth.

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