Although scientists have made great strides in understanding the nesting biology of leatherback turtles, little is known about the behavior of these critically endangered sea turtles at sea, where they spend most of their time. A pioneering field study by Earthwatch-supported marine biologist Dr. Scott Eckert (Wider Caribbean Sea Turtle Conservation Network) challenges notions about the swimming behavior of leatherbacks at sea, with important implications for their conservation.
The study, published in The Journal of Experimental Biology, employed a custom-built marine speedometer and other instruments to monitor the swimming behavior of female turtles between nesting attempts at Sandy Point National Wildlife Refuge, St. Croix, U.S. Virgin Islands.
"We learned that the species rarely stops swimming," said Eckert, currently a principal investigator for the Earthwatch-supported Trinidad's Leatherback Sea Turtles project. Eckert conducted the experiment as a principal investigator on Saving the Leatherback Turtle on St. Croix. "Leatherbacks use shallow surface waters for efficient transit swimming during long distance movements and migrations."
Eckert and Earthwatch team members equipped seven nesting female turtles with a combination of instruments, mounted on a harness, to monitor their swimming activity during the ten days between two nesting efforts. The instruments included velocity recorders, time-depth recorders, and radio transmitters.
Previous field studies by Eckert and colleagues showed that leatherbacks were the deepest free-diving creatures in the ocean, diving as much as 1,000 meters deep to feed on jellyfish. These same studies revealed that the turtles also spent time near the surface, suggesting that they were basking in the sun between feeding forays. The current study was the first to include the velocity recorders, which established that the turtles spend time near the surface to swim, not to rest.
It has long been known that the most efficient place for marine animals to swim is one-and-a-half to three times their body's diameter below the surface, deep enough to not create a bow wave but shallow enough to avoid the density of deeper waters. In the case of air-breathing turtles, it would also be advantageous to swim close to the surface, and it may also help turtles use a sun compass for navigation.
"But if turtles are swimming near the surface rather than basking, and they are not feeding, where on Earth are they going?" asked Eckert. The data from this field study also helped document the range of leatherbacks between nesting attempts, which will allow better management of marine areas around St. Croix for the benefit of the turtles.
Earthwatch teams on Trinidad's Leatherback Sea Turtles will primarily be monitoring nesting beaches to establish the size of this nesting population, one of the least known in the world. However, one team will be equipping a sample of turtles with satellite transmitters to give vital information on their movements and habitat use.
"Leatherbacks spend 99.9 percent of their lives at sea," said Eckert. "If we don't understand how the species behaves, where they go, what they do, during that time, we can't honestly believe that we understand the leatherback or what it needs to thrive."
For more information, see Eckert, Scott. "(Dermochelys coracea) at St. Croix, U.S. Virgin Islands." The Journal of Experimental Biology 205 (2002): 3689-3697
For information on volunteering on the Trinidad's Leatherback Sea Turtles project, click here
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