Forget Alligators, This Expert Wrestles Great White Sharks
for National Geographic News
|July 1, 2005|
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Great white sharks may be the poster child of marine predators. Yet scientists know surprisingly little about Carcharodon carcharias.
To map their movements and chart a course for the protection of great whites, one research team is getting up close and personal with the sea's top predator.
For three years Ramón Bonfil, a conservation scientist and shark specialist with the Bronx-based Wildlife Conservation Society, has been hand-fitting South Africa's great whites with dorsal-fin satellite tags. The tags reveal the sharks' day-to-day and long-term movements.
Bonfil's capture technique includes a heart-pumping face-to-face meeting with the king of the ocean food chain.
"It's a potentially dangerous situation, but we try to minimize the risk for both the scientists and the sharks," Bonfil said. "We don't want to kill a shark by mistake while studying it. Accidents can happen, so we're careful to work on nice flat water without risking more than we should."
Great white sharks can grow up to 20 feet (6 meters) long and weigh up to 5,000 pounds (2,270 kilograms).
Wildlife Conservation Society researchers began their shark-tagging project with "small" great whites, which still measured an impressive six to seven feet (two meters). The team has subsequently fitted animals measuring nearly 13 feet (4 meters) and weighing 1,650 pounds (750 kilograms).
The sharks are caught on a hook and line, and then maneuvered into a specially designed metal "cradle," which lifts them out of the water for three to seven minutes.
While researchers fix a satellite tag in the animal's dorsal fin, veterinarians pump seawater through the mouth and gills of the great white and inject drugs and vitamins that help the shark to recover from capture stress.
The entire process, from hookup to release, lasts about 15 adrenaline-filled minutes.
"When we did the first shark, we were very nervous, because we thought it would be thrashing and trying to bite everybody," Bonfil said. "But amazingly, when we took it out of the water, it was quiet and calm."
"As we started going to larger and larger sharks, they [became] very difficult to get into the cradle. But once in the cradle, they also became [quite] tame."
The release of a healthy shark may be the most perilous part of the procedure. "Some of the larger sharks, when they feel the water, once they feel that they are back in their element, they go mad," Bonfil said.
Though likely disconcerting for the sharks, the ordeal is ultimately for their own good. The satellite-tracking tags can help Bonfil and other scientists better understand great white shark migration patterns.
"Even though they are big, spectacular predators and one of the most immediately recognizable animals in the ocean, there are still profound gaps in basic knowledge [of great whites]," said Randy Kochevar, a marine biologist at California's Monterey Bay Aquarium. "How long do they live? Where do they breed? We don't know the answers yet."
Shark Life in 3-D
Satellite tags provide clues to such questions, because they allow scientists to track sharks in near-real time. Whenever a shark's tagged dorsal fin breaks the ocean surface, the device uploads a satellite radio signal. The feed can deliver data to desktop computers in one to two hours.
The tags track great white movements, enabling scientists to learn where and how the predators spend their time. Information on depth, water temperature, and light levels allows researchers to measure the animals' daily movements in 3-D.
Such technology has been a boon to shark researchers all over the globe.
"We try to imagine the world in which sharks live," Bonfil said. "Where do they spend their time on a day-to-day basis? On the surface? On the bottom?"
"[Without tags] we really don't have more than snapshot glimpses of what they do or how they use ocean habitat," Kochevar added. "As far as really understanding what their life is like over a 24-hour basis, we had no way to get that view at all [without tagging]."
The tagging data also reveals long-distance movements, migrations, and population dynamics that offer a clearer picture of larger shark society.
"To protect great whites we need to know their geographical range and their population structure," said Robert Hueter, who directs the Center for Shark Research at Mote Marine Laboratory in Sarasota, Florida.
"For these reasons, such studies are vital," he said. For example, Hueter wonders if the great white sharks found off the northeast U.S. coast are the same population found in the Mediterranean.
Great whites are heavily protected in South Africa, where Bonfil conducts his tagging project. But the shark researcher points out that such protection will mean little if the animals he studies routinely leave those waters for other regions where they are vulnerable.
Bonfil is currently awaiting data from great whites recently tagged near New Zealand, which could suggest whether those two populations are interrelated.
"Some [sharks] stay in a single spot for months at a time, and some move a lot," he said. "Unfortunately there is no pattern that we can identify as yet."
"This may be the largest-ever study of great white sharks' spatial dynamics, but it's still based on just 31 animals. We need much more data, and this requires better funding."
Hueter, of Mote Marine Laboratory, believes that further tagging research will reveal important patterns in shark distribution.
"I've been tagging [various] sharks for over 30 years, and one thing that's emerged is that these animals appear to show patterns of returning to specific areas," he said.
"It's very likely that great white sharks will have the same kind of patterns," Hueter added. "They're not mindless ocean nomads, but they are navigating to specific points, with flexibility, of course, for prevailing conditions. Finding out where those important habitats are located is critical for their protection."
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