NAPLES DAILY NEWS (Florida) ; Turtle expert hopes to test theory in Gulf (Jer...

NAPLES DAILY NEWS (Florida) 20 April 06 Turtle expert hopes to test theory in Gulf (Jeremy Cox)
Brimming with green turtles, a boat breaks up in a raging storm between Cuba and Key West. The turtles escape into the sea.
Months later and 600 miles away, the turtle fishermen recapture two of the turtles in almost the exact spot where they had been first caught off the northern coast of Nicaragua. The fishermen had branded their initials onto the turtles’ backs, so there was no mistaking their identity.
That anecdote and others, collected by the late University of Florida researcher Archie Carr in his 1956 book, “The Windward Road,” suggested that sea turtles use an extra sense to navigate great distances.
But how? That mystery puzzled scientists for years until a University of North Carolina at Chapel Hill biologist proved that turtles have a kind of internal Global Positioning System.
Ken Lohmann will discuss his landmark research tonight at Naples Community Hospital’s Telford building as the last speaker in the “Sea Secrets” lecture series. The University of Miami’s Rosenstiel School and the Ocean Research and Education Foundation are sponsoring the talks.
Lohmann, though, has an ulterior motive in this trip.
He wants to test his theories, which he developed on Florida’s Atlantic Coast, on Gulf Coast sea turtles. He plans to meet with David Addison, a leading researcher at The Conservancy of Southwest Florida, to discuss that prospect.
In a study, University of North Carolina-Chapel Hill biologist Ken Lohmann placed harnesses on sea turtle hatchlings and put them into a large tub to keep track of the direction they swam. His landmark research showed sea turtles use the Earth’s magnetic field to navigate great distances.
“It would be interesting to see if the hatchlings from the west coast have the same responses or if there’s some difference,” Lohmann said.
The Conservancy has been monitoring sea turtle nesting on Keewaydin Island for 25 years. Scientists know that once turtles emerge from their nests on the beach, they swim in a straight line due west into the Gulf of Mexico.
“Where they go from there, we might get some ideas from the work Ken does,” Addison said.
In general, sea turtle hatchlings on Florida’s east coast follow the Gulf Stream to the Atlantic gyre, a giant, circular current of water that encompasses the Sargasso Sea. There, sea turtles find few predators along with a ready supply of food in the form of floating sargassum weed.
On the Gulf Coast, where sea turtles nest in fewer numbers, hatchlings must eventually turn south and then east through the Florida Straits to reach the Gulf Stream.
How do hatchlings, with no navigating experience whatsoever, stay inside the protective gyre? And how are older sea turtles able to home in on favorite feeding areas from great distances away?
Certain migratory birds and fish, particularly salmon, are known to use the earth’s magnetic field to reckon direction.
For years, scientists suspected that sea turtles also possessed a “magnetic sense,” but there were competing theories. One proposed that sea turtles follow trails of chemicals in the ocean.
“Virtually nothing was known at the time about how sea turtles guide themselves through the ocean,” Lohmann said.
Here is a brief explanation of how magnetic sensing works:
Each part of the globe has a unique magnetic pull. For an animal to form what Lohmann calls a “magnetic map,” it would have to learn to distinguish between slightly different magnetic fields.
When diagrammed, the magnetic lines resemble ripples of water surrounding the Earth. They emerge from the Southern Hemisphere and wrap around to the top of the planet. Because of this gentle arc, the lines strike the planet at different angles, progressing from 0 degrees at the equator to 90 degrees at the North Pole.
Once a sea turtle has memorized the angle of inclination at its favorite patch of sargassum, it can easily find its way back.
On his Web site, Lohmann explains the phenomenon this way: “If the angle is too steep, the turtle knows that it is too far north and therefore needs to travel south to reach home. If the angle is too shallow, then the turtle knows it is too far south.”
To confirm this theory, Lohmann and a team of researchers captured several juvenile green turtles in a feeding area off Melbourne Beach. The researchers placed the turtles in a large blue bucket surrounded by a coil system that, with a surge of electrical current, could generate a weak magnetic field around the turtles.
Half of the turtles swam in a field that replicated what would exist off the southern coast of Georgia, 210 miles north of Melbourne. The other half were tricked to think they were the same distance away, except off the coast of Key Largo.
The turtles swam in place, apparently unaware they were in nylon harnesses and tethered to a rotatable lever. The “northern” turtles swam to the south while the “southern” turtles headed north.
Lohmann and the other researchers published the study in the April 2004 issue of the prestigious journal Nature.
Understanding the sensory world of sea turtles is important for their conservation, Lohmann said. Every sea turtle species that frequents Florida’s waters is listed as either endangered or threatened.
The night with Lohmann begins with a reception at 5:30 followed by the lecture at 6:15. The event is open to the public. Seating is limited.
Turtle research
Ken Lohmann will discuss his landmark research tonight at Naples Community Hospital’s Telford building as the last speaker in the “Sea Secrets” lecture series. The night with Lohmann begins with a reception at 5:30 followed by the lecture at 6:15. The event is open to the public. Seating is limited.
http://www.naplesnews.com/news/2006/apr/20/turtle_expert_hopes_test_theory_gulf/?local_news