Scientists can identify zebras by their "bar codes"–now they can identify shark fins by zip code. Shark fins are illegally poached by the Chinese in order to make one of their great delicacies: shark fin soup. Tens of millions of animals are killed every year to produce this: 73 million sharks are killed by people every year, while sharks kill 4-5 people a year.

The Chinese are sometimes hard for Westerners to understand: For instance, shark fin soup is actually watery and tasteless if made only with shark fins–it’s the pork and chicken in it that gives it its taste. Eating it is a kind of "bravado" statement in China, a celebration of winning the battle with a dangerous animal.

Sharks must swim constantly in order to get oxygen from the water flowing through their gills, thus removal of their fins kills them. This dangerous practice may lead to the extinction of certain species of shark. There is already a 90% decline in some species. Females hit hardest because they are bigger with larger fins, which makes it more likely that a species will die out.

By analyzing the shark carcasses they find, scientists can determine where they were swimming when their fins were removed. Sharks have predate the dinosaurs: They’ve been around for 400 million years. Archeologists don’t find their bones (since they don’t have any). Instead, they date them from finding their TEETH. Many of these shark teeth are found in Montana, which was once covered by the ocean.

The dusky shark is classified as "Endangered" in the Western Atlantic by the International Union for Conservation of Nature as its population is below 20% of what it was two decades ago. These new studies show that the genetic differences among populations of these sharks are large enough for scientists to be able to track the actual origin of the fins on sale in Asian markets, enabling better regional monitoring and management of these threatened predators.

Sharks are caught all over the world (even off the coast of South America), but all shark fins are shipped to China, where they are sold at auction. They are traded like commodities are in the US and Europe. Oceanographer Demian Chapman says, "By analyzing part of the genome that is inherited solely through the mother, we were able to detect differences between sharks living along different continents–in effect, their DNA zip codes. This research shows that adult females faithfully give birth along the continental region where they were born. If fished too much, the population will collapse, and it is extremely unlikely that it will be replenished from immigration of sharks from another region."

At one time, these animals were common in ocean waters off the United States–however, a recent stock assessment of the sharks along the US East Coast and in the Gulf of Mexico showed an 80% decline even though they have been protected since 2000 (NOTE: Subscribers can still listen to this show). The recovery of the species is extremely slow because the average age of maturity is 20 years, its reproductive cycle only occurs every three years–including a two-year pregnancy–and its litter size is relatively small (three to 14 offspring).

So why do we need sharks, anyway? They are a major ocean predator that keeps mid-level predators at bay. Without sharks, mid-level predators will decimate things in the ocean that WE like to eat, like oysters and scallops. An absence of sharks is the reason that piles of jellyfish have been washing up on many shores recently.

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