Crittercam Sea Turtle Study May Aid Conservation
for National Geographic News
|February 12, 2004|
This story is one of a series looking at National Geographic
Crittercam research. Crittercam is a research instrument worn by wild
animals and equipped with a video camera and other
information-gathering equipment. (Get the basics on underwater and terrestrial Crittercams.)
For more on this story, tune in to the Crittercam: Turtles episode on the National Geographic Channel in the U.S. Watch video previews online.
Sea turtles around the world are on a slippery slope toward extinction, but in Shark Bay, on the remote coast of Western Australia, two species of the ocean-dwelling reptiles thrive among a flourishing diversity of life.
"Shark Bay gives us a glimpse of what other marine habitats might have been like before they were changed by people," said Mike Heithaus, a marine biologist at Florida International University in Miami.
He and other researchers are learning why why Shark Bay is a flourishing ecosystem. They hope their findings can help with conservation efforts in stressed parts of the world's oceans, where the larger animals are losing the battle to survive.
In Shark Bay loggerhead and green sea turtles graze and swim among vibrant beds of sea grass with dugongs, bottlenose dolphins, and six species of sea snakes.
As the name of the bay suggests, tiger sharks (Galeocerdo cuvier) lurk nearby, waiting for opportune times to attack. Many loggerheads, in particular, bear wounds from narrowly escaping the jaws of death.
Since 1997 Heithaus has studied how the major marine species in Shark Bay interact. His work is part of an ongoing project initiated by Larry Dill, a marine biologist and Heithaus's former advisor at Simon Fraser University in British Columbia, Canada.
Understanding how the sea grass ecosystem functions in Shark Bay may help rehabilitation efforts in more impacted areas, such as the United States' Florida Bay in the U.S. and parts of the Caribbean, Dill said.
"Many habitats have been destroyed, but at some sites people are interested in trying to restore them," Dill said. "But we don't have many examples of functional sea grass ecosystems to use as a baseline. Shark Bay happens to be in good shape."
In years past the researchers have studied the bay's tiger sharks, dolphins, dugongs, and sea snakes. They've now turned their attention to the sea turtles to help round out the picture, Heithaus said.
One of their biggest questions is why the loggerheads bear so many wounds from tiger shark attacks but the greens appear relatively unscathed. National Geographic sent the Crittercam team to Shark Bay to help the researchers find answers.
The Crittercam footage and more about Shark Bay can be seen on the National Geographic Channel TV special Crittercam: Green and Loggerhead Turtles.
Healthy Populations, Imperiled Individuals
Unlike their counterparts in most of the world, the tiger shark and sea turtle populations in Shark Bay are healthy and robust. The turtles have evolved to deal with predation by the sharks, reaching an equilibrium that places neither shark nor turtle at risk of extinction.
"But individual turtles are certainly in peril, and they have to make good decisions about where to spend their time and how to behave if they are to avoid the sharks," Heithaus said.
The green sea turtles average 3 feet (1 meter) long and 350 pounds (160 kilograms). Their long flippers, sleek bodies, and smooth shells allow them to zip through the water at speeds greater than 10 miles (16 kilometers) an hour.
The researchers theorized that perhaps the greens' speed allows them to escape tiger sharks more readily than loggerheads can. Loggerheads are about the same size as greens but are handicapped by stubby flippers and barnacle-encrusted shells.
But the researchers were in for a surprise.
"The Crittercam showed us the loggerheads spending a lot more time at the surface than the greens, and based on the behavior of tiger sharks, that seems to be a really bad thing to do," Heithaus said. "It is probably one of several reasons we see a lot more injured loggerheads than greens."
The researchers are uncertain as to why the loggerheads spend so much time gulping for air at the surface. The team believes the practice may have to do with a difference in the species' diving abilitiesthe loggerheads may not be physically capable of diving after just a few quick breaths.
The footage also revealed a few tidbits about the greens. For one, they keep their shells nice and polished by rubbing up against sea sponges. Also, jellyfish make up a much greater percentage of their diet than the researchers had suspected.
Heithaus and his colleagues hope future deployments of Crittercam on Shark Bay's sea turtles will reveal how they change their behavior based on the presence or absence of tiger sharks.
Dill said such information could be important in helping devise schemes to prevent sea turtle deaths due to human factors such as boat traffic.
"We're thinking of boats as analogous to predators, so how [the sea turtles] react to predators may be similar to how they react to boats," he said. For example, Dill said, the presence of a predator may force a sea turtle to dive before it is ready, thus affecting how much it can forage while underwater.
Such knowledge, Heithaus said, "might help us figure out how to change human behavior to minimize the impacts on the turtles."
In addition to Heithaus and Dill, project scientists include Linda Heithaus of Florida's Mote Marine Lab; Simon Fraser University graduate students Aaron Wirsing and Alejandro Frid; and graduate student Lars Bejder of Dalhousie University in Halifax, Nova Scotia.
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