Satellites Spy on Lives of Great White Sharks
National Geographic Today
|September 22, 2003|
Last May, a small fishing boat plied the waters of Mossel Bay, South Africa, in pursuit of great white sharks. Scientists hooked a seven- footer, fought the fish for a couple of minutes until it calmed, then towed it towards the 100-foot (30-meter) research vessel that waited nearby. The team onboard guided the shark into a metal crib, and hoisted it on deck with a hydraulic lift.
Marine biologist Ramon Bonfil and four South African colleagues leaped into the crib with the shark, steering clear of its fearsome jaws. After quickly covering its eyes, they power-drilled small holes in the animal's dorsal fin and bolted on a small satellite transmitter.
A veterinarian pumped water over the animal's gills and administered antibiotics and vitamins to counteract the stress of capture. Others measured and sexed the animaland in under five minutes, the shark was back in the water, swimming away.
"We were like a Formula One pit crew," said Bonfil, a shark expert with the Wildlife Conservation Society in New York City who heads the project.
The team tagged eight sharks with "real time" transmitters. These instruments track the sharks' day-to-day movements for three to six months, sending the data to Bonfil's laptop via email each time their fin breaks the surface. "They're very large animals, so potentially they can swim very long distances, but do they?" asks Bonfil.
The great white shark is the largest predatory fish, much-feared and greatly maligned by humans. But despite their notoriety, little is known about their basic biology or habits, their numbers, where they gowhere they mate and birth their young remains a mystery.
To answer these questions, scientists are using two types of satellite transmitters to track the whereabouts of great white sharks from each of the world's hotspots: South Africa, California, and Australia.
In 2002, he began tagging sharks in collaboration with the South African government and the Universities of Cape Town and Pretoria, originally fitting 16 sharks with pop-up tags. The team will return in November to fit another 26 sharks with both types of transmitters.
A second type of transmitter, a pop-up archival tag, is easier to attach and gives scientists different information. From aboard ship, it is darted into a shark's back. This tag collects data on water temperature, dive depth, and light levels once every minute for up to 12 months. Then it is electronically detached from the shark. When it floats to the surface, it uploads the data, along with its position, to a French satellitewhich is then beamed to scientists' computers.
State of the White
Shark populations have declined over recent decades. Sharks first appeared in ancient oceans 400 million years ago, evolving into apex predators, but they are not able to withstand predation today by humans.
Great whites are pursued by trophy-hunting fishermen for sport and for their jaws, which can fetch tens of thousands of dollars. Many also die as bycatch, drowned on commercial longlines or in gill nets that catch everything that swims by.
A recent study by scientists at Dalhousie University in Nova Scotia, Canada, revealed that North Atlantic great white shark populations fell by 79 percent from 1986 to 2000.
Depleted populations are slow to recover. Great whites grow slowly, not reaching maturity until around the age of 12, and then produce few offspring. Globally, they are classified as a vulnerable species.
Great white sharks are protected off coastal waters in just five nations, including South Africa, the United States, Malta, Namibia, and Australia. But these countries' 200-mile-wide (322 kilometers) coastal areas may prove insufficient to protect great whites from fishing fleets. "The problem is that there aren't any global conservation laws," said Andre Boustany, a marine biologist at Stanford University in Palo Alto, California.
Tracking Great Whites
Tagging sharks is a difficult process and transmitters are expensive, but this technology is helping to identify great whites' home rangesand how much time they spend outside protected areas.
Researchers at Stanford began tagging sharks off California's Farallon Islands in 1999. Studies had revealed that whites congregated there from late summer to early winterthen disappeared. "We wanted to figure out where they were the other half of the year," said Boustany.
"The most startling discovery was how much time these sharks were spending thousands of miles from land." One shark traveled 2,360 miles (3,798 kilometers) to Hawaii. Another three were tracked to the subtropical eastern Pacific between Baja California and Hawaii, about 1,500 miles (2,414 kilometers) from land.
They spent up to six months thereand did lots of deep diving, down to nearly 2,000 feet (610 meters). Subsequent tagging corroborated these routes.
"We assumed that these were coastal fish, hanging out in temperate waters, but found out that they spend about half their life in deep, subtropical waters," said Boustany.
To adjust from temperate 50- to 60-degree waters (10-16 degrees Celsius) to 80-degree (27 degrees Celsius) subtropical waters, the sharks may have some thermo-regulatory ability, says Michael Domeier, president of the Pfleger Institute of Environmental Research in Oceanside, California, whose team tracked whites who spend half the year near Guadalupe Island off Baja.
Both Domeier's Mexican whites and Bonfil's South African whites also showed wide-ranging, deep-diving behavior. Bonfil followed one shark over three months that traveled 1,000 miles (1,609 kilometers) into unprotected waters in Mozambique.
Other researchers documented the same behavior across the globe. In 2000, scientists with the Commonwealth Scientific and Industrial Research Organization in Victoria, Australia, traced a young male shark's route from the Victorian Coast to Tasmania and back1,830 miles (2,945 kilometers) in 129 daysuntil communication was lost.
Spying on Great Whites to Protect Them
Ultimately, researchers hope these studies will provide the scientific evidence needed to better protect great whites. Defining migratory routes and birthing grounds could help conserve sharksand be used in public safety, said Domeier.
"We're finding that [California whites] spend half or more of their time in international watersso we need international management to protect them effectively," said Boustany.
Bonfil would like to see the sharks listed as part of the Convention on International Trade in Endangered Species, which could limit or prohibit trade in jaws and other great white parts. "They're not the killing machines we see in the movies," said Bonfil. "They are a potentially dangerous top predator, like a lion or a tiger, that has an important role in the ecosystem," said Bonfil.
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