Seattleites who dined on shark-fin soup before the state banned it may have been slurping down species of shark that conservation groups consider threatened, according to a study released Thursday.

The Pew Environment Group, which conducted the study, analyzed the shark meat found in 51 bowls of the traditional Chinese delicacy from 14 U.S. cities, including one from Seattle.

The researchers found meat from the school shark — also known as the soupfin shark — in the Seattle soup, a species classified as "vulnerable" by the International Union for Conservation of Nature. School shark was also found in bowls from Las Vegas, San Francisco and Orlando, Fla.

A bowl from Boston contained meat from the scalloped hammerhead, an endangered species. And soup from other cities contained such species as spiny dogfish, shortfin mako and smooth hammerhead, all considered vulnerable.

Washington state banned the sale of shark fins last year, making it illegal for restaurants to serve the soup, which can cost as much as $100 per bowl. Anyone caught with $250 or more worth of shark fins can face felony charges.

"I'm appalled to hear that we're still finding the fins in soups in restaurants in Washington state," said state Sen. Kevin Ranker, D-San Juan Island, who sponsored the bill banning the trade.

The trade in shark fins claims up to 73 million animals a year, he said, and the school shark has been especially affected. "It makes this that much more disheartening," he said.

It is unclear whether the Seattle restaurant from which the researchers bought the soup was selling it illegally.

Though the ban took effect in July last year, the bill carved out an exemption for restaurants that already had the dried fins in stock. Pew bought the soup in March, said Rachel Brittin, a Pew spokeswoman, so the soup may have been legal to sell if it was made with old shark fins.

Ranker was dubious. "That would mean they've been holding that shark fin for almost a year," he said of the restaurant. "I find that hard to believe."

Pew declined to name the restaurant, but Brittin said researchers found it using Yelp.

Washington was the second state to ban the trade in shark fins, after Hawaii. Bans have since been passed in California, Oregon and Illinois as well.

Determining which sharks were showing up in the soup presented a scientific challenge for the researchers who conducted the study. Shark fins are typically dried and treated with sulfur or hydrogen peroxide before being cooked at high temperatures, which can mutilate the DNA.

To crack the code, researchers at the State University of New York at Stony Brook washed the pieces of shark fin from the soup and extracted DNA using a fairly standard method. They then isolated part of a single gene and made millions of copies of it.

Scientists from the Pritzker Laboratory at the Field Museum in Chicago sequenced the snippets of DNA and then compared them with DNA from the GenBank, a kind of library of genetic codes, to find matches.

"I was surprised that it worked at all, to tell you the truth," said Kevin Feldheim, who led the Pritzker Lab's work.

The researchers were able to identify the species of shark the fins came from in 32 of the 51 bowls of soup; 81 percent of the sharks were classed as endangered, vulnerable or "near threatened."

Pew has teamed up with shark-attack survivors, including Debbie Salamone, a spokeswoman for Pew, to promote the study. Several of them will be featured on the show "Shark Fight" next week on the Discovery Channel, which is part of the network's popular Shark Week.

"We hope this study makes people think twice about what they're consuming," Salamone said.

Theodoric Meyer: 206-464-6805 or tmeyer@seattletimes.com. Twitter: @theodoricmeyer.