Shark attack survivors collected 32 shark fin soup samples from 14 cities across the United States. DNA analysis indicated that 26 bowls contained fins from sharks listed as endangered, vulnerable or near threatened.
The endangered shark species -- scalloped hammerhead -- was found in a sample from Boston. Other shark species in the samples included smooth hammerheads, school sharks and spiny dogfish, which are all listed as vulnerable to extinction; and other near threatened species such as bull and copper sharks.
Liz Karan, manager of global shark conservation at the Pew Environment Group, a global conservation advocate, said in an online statement that the study is further proof that shark fin soup in the United States -- not just in Asia -- is contributing to the global decline of sharks.
Karan said there was no way consumers could identify the type of sharks in their soups. She said people ordering the soup might be consuming an endangered species without knowing it.
"Think twice before ordering it," she said.
The soup, brewed from dried shark fins, is largely tasteless but is considered as a symbol of wealth in Asian countries. The delicacy is almost a must-have in banquets to celebrate weddings, anniversaries and important corporate and state events.
Demian Chapman, assistant director of science at the Institute for Ocean Conservation Science at Stony Brook University and co-author of the study, said he wasn't surprised at all by the results because shark fin trade is "very, very poorly regulated."
"The fin soup in the U.S. is not necessarily from sharks caught in the U.S.," he said. "It might be imported. Globally speaking every nation gets very poor marks monitoring this international trade."
U.S. President Barack Obama signed the Shark Conservation Act into law in 2011. The act addresses loopholes in a law passed a decade ago in an effort to curb shark finning, the practice of cutting off a shark's fins and dumping its body overboard, sometimes when it is still alive.
The new law requires any vessel to land sharks with their fins attached and prevents non-fishing vessel from transporting fins without their carcasses.
China, one of the biggest markets for shark fins, said in July that it would ban shark fin soup from official banquets. Though there is doubt as to how effective the order is in provinces far away from the central power, experts say it is a significant step forward.