Florida`s Sea Turtles New Research Sheds Light On How Hatchlings Find Ocean.

July 19, 1992|By STEPHEN d`OLIVEIRA Staff Writer

Under moonlight shimmering on the sea, more than 6 million tiny sea turtles will squeeze through their egg shells and scamper across Florida`s beaches this year in a perilous life and death journey.

Few will survive.

For decades, scientists said the hatchlings found the Atlantic Ocean by instinctively following the light of the moon on the horizon.

Two Florida Atlantic University marine biologists who study sea turtle behavior are challenging that commonly held theory.

Professors Mike Salmon and Jeanette Wyneken conducted laboratory experiments that indicate that moonlight plays no role in helping sea turtles locate the ocean.

Instead of being attracted to light, Salmon said, the hatchlings see ``dark and/or high objects`` and find the ocean by heading in the opposite direction.

``What they see that is dark and high is the dune and vegetation,`` said Salmon, chairman of FAU`s biological sciences department in Boca Raton.

What may have led scientists to think turtles were attracted to natural light is the well-known fact that they are drawn to artificial light.

Whenever sea turtles, which hatch at night, emerge from their shells along heavily developed beaches, they scurry toward the bright streetlights and are crushed by cars.

Salmon said scientists call this ``light trapping,`` the same phenomenon that draws moths to flames and insects to electric bug zappers.

Salmon said the sea turtles are disoriented by the bright light source and head toward it in confusion.

``The influence is overwhelming,`` Salmon said. ``These animals are just totally unprepared for the kinds of lights we produce. It totally upsets their normal orientation system.``

For three decades, scientists theorized that sea turtles were attracted to the ocean by light of the moon and the stars.

The moon theory, however, does not explain how hatchlings find the ocean where there is no moon in the night sky, or when the moon appears in the western sky.

``The moon business is just poppycock,`` Salmon said. ``That`s just nonsense. They`re going away from the dark silhouette of the dune, and that takes them to the ocean.``

Salmon isn`t the first to suspect that natural light has nothing to do with how sea turtles find the ocean. About two decades ago, Salmon said, other researchers first suggested that it might not be true. Subsequent studies also hinted at it.

Salmon and Wyneken conducted recent laboratory experiments in which they simulated artificial horizons, silhouettes and moonlight shimmering over the ocean.

``We played all sorts of games,`` he said.

They placed a dark silhouette under a bright light source. In other words, they put what the sea turtles would view as a sand dune directly beneath where the moon and seas would be.

The hatchlings ignored the light and traveled in the opposite direction.

``No matter where we put the dark silhouette, they always went away from it,`` Salmon said.

Salmon and Wyneken will publish their findings this fall in Behaviour, a scientific journal printed in Holland.

Once the hatchlings enter the water, where they can be eaten by sharks, birds, dolphins and other predators, they frantically swim for 24 hours.

Salmon said their destination is the North Atlantic Gyre, a large clockwise ocean current that transports seaweed and other debris on a journey of 12,000 miles spanning four continents.

``The currents are just taking them around and around,`` he said, saying researchers think the hatchlings spend their first few years floating in the currents.

Some scientists say their survival rate is 1 in 100. Some say it`s 1 in 1,000. Still others say it`s 1 in 10,000.

``No one knows for sure, but it`s a very small percentage,`` Salmon said. ``Very few of them survive, so they lay a lot of eggs.``

Mature sea turtles eventually return to the same general area where they hatched to breed and lay new eggs, starting a new cycle of life.

``It`s still an amazing feat,`` Salmon said. ``We don`t know how they do it. We only know that they can.``

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