genetics to identify sharks exploited by the international shark fin trade in the southwestern Atlantic have found a previously unknown species of hammerhead shark closely related to scalloped hammerhead sharks. The two species share the same waters but do not interbreed.

These sharks look the same as scalloped hammerhead sharks but occur in much smaller numbers so their population is very vulnerable to the shark finning trade - cutting off a shark's fins and discarding the carcass - which is practiced around the world because fins are believed to have aphrodisiacal and medical benefits in the Far East. Hammerhead sharks are particularly vulnerable because their fins are worth hundreds of dollars per kilogram in markets in the Far East, while their meat has little value. The population of hammerhead sharks in the western Atlantic is thought to have declined by 89 percent since the mid-1980s, according to a study by researchers at Canada's Dalhousie University published in 2003.

While trying to develop a DNA forensic marker for scalloped hammerheads, the scientists collected 143 samples of Sphyrna lewini from around the world but found that their test worked on all of the sharks except for three, which were caught by recreational anglers off Fort Lauderdale. At first, the scientists thought something was wrong with their test but further testing on the three sharks from Florida showed that their DNA was completely different from all other scalloped hammerheads caught locally and around the world, suggesting that they were a separate species. The genetic difference was greater between the new species and regular scalloped hammerhead sharks than between the geographically separate populations of scalloped hammerhead sharks.

Scientists at the University of South Carolina have reached the same conclusion using genetic testing on sharks caught in their coastal waters.

As yet the species does not have a name and no one knows how big the population may be.