A new study suggests that consumers in the United States might be unknowingly eating an endangered species in the shark fin soup.

Researchers from the Stony Brook University in collaboration with Field Museum in Chicago and Pew Environment Group performed a nationwide DNA analysis of shark fin soup for the first time and found that at least four endangered species of sharks in 32 samples of soups served across 14 cities in the country.

The four shark species include smooth hammerheads, scalloped hammerheads, school sharks and spiny dogfish, all of which are listed as vulnerable to extinction by the global environmental network, International Union for Conservation of Nature (IUCN).

Besides the four species, the researchers also found "near threatened" species such as bull and copper sharks being used in the soup.

"The DNA testing again confirms that a wide variety of sharks are being killed for the fin trade, including seriously threatened species," Dr. Demian Chapman, who co-led the DNA testing at the Institute for Ocean Conservation Science at Stony Brook University in New York, said in a statement from the Institute for Ocean Conservation Science.

"U.S. consumers of shark fin soup cannot be certain of what's in their soup. They could be eating a species that is in serious trouble," he said.

Researchers pointed out the analysis provides evidence that the shark fin soup is one of the contributors to the global decline of sharks.

In a recent study by researchers from the UK and Portugal, they pointed out an alarming 80 percent decline of blue sharks in some regions off the British coast could be due to an increasing demand for the shark fin soup in Asia.

According to a report from Pew, around 73 million sharks are killed every year for their fins. Sharks have a slow birth rate and low growth rate that makes them vulnerable to overfishing and recover slowly from the population decline. This, in turn, affects the entire ecosystem of the ocean.

Researchers insisted that sharks need to be protected from overfishing and from being traded to prevent their population decline.