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Satellite Tags to Solve Hammerhead Mating, Migration Mysteries?

Adrianne Appel
for National Geographic News
February 1, 2006
 
How far would you go to save a species? When it comes to great
hammerhead sharks, Wes Pratt shows more mettle than most.

In a few weeks, the marine scientist will attach satellite-tracking tags—by hand—to two of the 500-pound (230-kilogram), 12-foot (3.7-meter) predators as they feed off the Bahamian coast.

Pratt, a biologist at the Mote Marine Laboratory Center for Shark Research, in Summerland Key, Florida, hopes the tracking data can help garner protections in the Bahamas for the rare species.

"We need to establish their activity patterns and where their nursery is," he said, adding that he also hopes to learn whether the sharks have a mating season.

Pratt and his colleagues will conduct underwater observations and record video of the sharks during their field research, which is funded in part by the National Geographic Society's Expeditions Council.

Limited Protection

Named for its large size and the hammer-like shape of its head, the great hammerhead (Sphyrna mokarran) is one of nine hammerhead shark species.

Why the sharks developed such an odd head shape isn't known. But it does create a larger surface area for special sensory organs embedded in their skin.

Sharks rely on the pore-like electrical sensors, known as ampullae of Lorenzini, to pinpoint their prey at ultra-close range.

That prey includes stingrays, which the sharks hunt in subtropical coastal and deep ocean waters.

The great hammerhead is somewhat protected while it swims in United States coastal waters, where commercial fishing of large sharks is allowed but restricted.

A number of other nations also protect the species. But most do not, and the great hammerhead is not protected when in international waters.

"It's rare and wonderful to find them," said Pratt, who has spent 37 years studying sharks.

"Gentle Touch"

George Burgess, director of the Florida Program for Shark Research at the Florida Museum of Natural History, said: "Hammerhead sharks are very uncommon attackers of human beings."

He says there are just 17 known human attacks by hammerheads. By comparison, Florida beachgoers endure an average of 20 to 30 shark attacks each year, mostly by the black tip shark, according to Burgess.

Still, the great hammerhead is a large predator, and Pratt says his tagging endeavor will be done very carefully to protect both his team and the sharks.

A guide will bring Pratt, a photographer, and fellow researchers to a secluded spot off the Bahamas where the sharks feed.

There, Pratt's team hopes to catch two great hammerheads, using baited hooks on thousand-pound test line.

Once the fish are reeled boat-side, the work gets intense.

"You orient the head and someone else grabs the tail and puts a noose around it. A third person tags and a fourth person records data," such as length, gender, scars, and general condition.

Hammerheads tend to get overstressed when caught and die if they are not handled quickly and carefully.

"We may put a towel over the eyes and put a hand on them. I think they pick up on the good vibrations [from] a gentle touch," Pratt said.

The biologist will punch two holes in the shark's dorsal fin, which doesn't bleed, and attach the microphone-shaped satellite tag with a cable.

"When everybody is OK, we release the tail, hold the hammer securely, and remove the hook. They usually burst off by themselves," Pratt said.

Ideally, in three months the tag will pop off and float to the surface. It will then be able to transmit information about where the shark has been and the depths it has gone to.

Overfished

Pratt's data may get the ball rolling on international protection for the great hammerhead.

The International Union for Conservation of Nature and Natural Resources, which provides guidance to governments about species protection, currently lists the shark as data deficient.

The U.S. National Marine Fisheries Service considers large sharks to be overfished.

The agency is currently assessing whether a fishing restriction it imposed in 2003 as part of a 26-year plan to increase shark numbers has helped boost the number of large sharks.

The regulation allows fishers to take 2.2 million pounds (1,017 metric tons) of large coastal sharks annually from U.S. waters. The U.S. prohibits fishing sharks solely for their fins, which are a delicacy in Asia.

In the early 1990s the U.S. government encouraged fishers to take sharks, which were viewed as abundant, instead of swordfish and tuna. Today fishers sometimes unintentionally haul in sharks when pulling in other fish.

Burgess, of the Florida Museum of Natural History, says humans kill about 400,000 sharks each year.

"When an animal like a shark, skate, or ray is overfished, recovery will be measured in decades," unlike short-lived species like the anchovy, Burgess said.

Sharks do not begin reproducing until they are 10 to 12 years old or older, and their gestation lasts 12 to 18 months.

Ramon Bonfil, a great white shark expert with the Wildlife Conservation Society in the Bronx, New York, said little is known about the hammerhead and other sharks because "funding for shark research is appallingly poor."

The reason, he says, has everything to do with society's unfavorable image of sharks.

"No matter how dangerous [sharks] are, they are not monsters, and we need them and we want to conserve them," Bonfil said.

The species deserve the same concern that many people give to whales, dolphins, and big cats, he says.

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