With its big flippers, flexible shell, and insulating layer of blubber, the leatherback turtle (Dermochelys coriacea) seems well suited for life in the ocean. Yet we know almost nothing about how these rare reptiles swim around in the wild. How fast do they go, and how far can they swim in a day? By tracking seven female leatherbacks with radio transmitters and velocity recorders, Scott Eckert, of the Hubbs-Sea World Research Institute, has discovered that contrary to popular belief, momma turtles are outstanding endurance swimmers that travel over great distances with hardly any rest (p. 3689)!
Keeping up with sea turtles can be gruelling, Eckert admits. By day, he's out on the water searching for leatherbacks and monitoring their movements. By night, he's trudging up and down the beaches of St. Croix (US Virgin Islands) looking for nesting females. When he finds one, he puts a simple harness on the animal, attaches his recording instruments, and waits to see what the turtle does once it leaves the beach. “Leatherbacks are pretty easy to deal with,” says Eckert. “They don't bite, and they don't run away.”
Previously, Eckert had tracked how deep the turtles dived in the ocean, and he found that they spent a lot of time at the surface during midday. This made him think that leatherbacks might be basking in the sun to rest after a long night of diving for food. But he hadn't measured how fast they moved. The only way to really understand how the animals behave in the wild was to track their speed as well as their depth.
But the only previous measurements of leatherback swimming speeds weren't completely reliable, because they were made while animals were being pursued by boat. So, Eckert had a “turtle speedometer” custom-built. When females came to the beach to nest, he attached both the speedometer and a depth meter to their backs and recorded what they did once they returned to the water.
To his surprise, instead of putting their fins up and taking a rest at the surface, the turtles hardly ever stopped swimming, whether it was day or night! And they managed to keep up a high speed too, swimming continuously near the surface at 0.6 m s-1 and travelling 50 km per day. So rather than being layabouts, leatherbacks are true masters of the marathon. Eckert also noticed that the turtles tended to dive down below 100 m during the day (sometimes exceeding 500 m), but at night the dives were shallower and more frequent, matching the whereabouts of their favourite snack — jellyfish.
Eckert would now like to know how their diet and metabolism help make them such economical swimmers and divers. Ultimately, he hopes that we can use this information to design more effective conservation strategies to protect this endangered species. If we understand the physiology of leatherbacks as well as their migration and feeding patterns, Eckert explains, we can better define how the species uses critical ocean habitats. That would help us reduce the impact of human threats like fishing nets, boats, and plastic bags. Seeing as these majestic creatures have been around for 90 million years, it seems the least we can do.
- © The Company of Biologists Limited 2002