Monday, April 24, 2006

UM Researcher Investigates Strange Shark Gathering

(AP) FT. LAUDERDALE For a man who had spent a lifetime researching sharks, what Samuel Gruber saw diving four years ago off the Jupiter Inlet was nothing short of a religious experience.

About 100 adult lemon sharks hovered over the ocean floor in about 90 feet of water.

Throughout his 40-plus-year career, Gruber had seen maybe 15 or 20 adult lemon sharks, distinguished by their yellowish brown tint and dual dorsal fins.

"In one day I saw more adults by a power of five than I have in my whole career," said Gruber, 67, who has visited the site between December and March every year since.

Nowhere else in the world does such a phenomenon exist, Gruber said. And Gruber, among the world's leading authorities on sharks, has been trying to answer a simple question: What brings them here?

Gruber's initial theory is that female sharks are emitting chemical signals called pheromones that attract male sharks. But why they've chosen this particular spot to conduct their courtship remains a mystery. Does it have something to do with a combination of the currents, water temperature, and its salinity?

This year, getting closer to those answers proved more difficult. Not nearly as many sharks showed up.

The number of sharks fluctuates from year to year, Gruber said, and he's confident that more sharks will return. "You have good years and you have bad years," he said.

Next winter, he hopes to start testing his theory. He plans on collecting water samples around some of the female sharks and testing the water chemistry or possibly extracting urine samples from the females.

Juvenile lemon sharks are relatively easy to study. They congregate in nurseries in bays or lagoons. They prefer the safety and plentiful food supplies at mangroves and in warm shallow waters, such as those at the Bimini Biological Field Station, about 50 miles east of Miami, which Gruber owns and runs.

Read the whole thing here.

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