The National Marine Fisheries Service on Thursday classified as endangered and threatened four populations of a shark species whose fins are favored as an ingredient in shark fin soup.

The agency said it's listing scalloped hammerhead sharks in the eastern Atlantic and eastern Pacific oceans as endangered, which means they're at risk of becoming extinct.

The populations in the central and southwestern Atlantic and the Indo–West Pacific are being listed as threatened, which means they're likely to face the risk of extinction in the future.

The central Pacific population, which includes scalloped hammerheads living in Hawaiian waters, is considered fairly healthy and isn't being listed.

The new classification responds to a petition filed by the environmental groups WildEarth Guardians and Friends of Animals.

"The listing of the scalloped hammerhead is an important indication that the human exploitation of marine species has taken its toll," said Michael Harris, the director of the wildlife law program at Friends of Animals.

The classification takes effect in September. Once listed, federal agencies will have to make sure their actions don't jeopardize the species or harm the species' critical habitat.

Scalloped hammerheads will receive international protections the same month from the Convention on International Trade in Endangered Species of Wild Fauna and Flora. Under the new CITES designation, trade in scalloped hammerheads will be allowed only if an exporting country issues a permit after finding the sharks were legally acquired and determining that selling them won't harm the survival of the species or its role in the ecosystem.

Carl Meyer, a shark researcher at the Hawaii Institute for Marine Biology, said demand for shark fins is driving overfishing of the species. The high number of fibers in scalloped hammerhead fins makes them particularly desirable for shark fin soup, he said.

Fishermen are catching juveniles as well as adults.

"Of course, if you take away all of the small ones, then you don't get any big ones, and then your population starts to really decline dramatically," Meyer said.

Scalloped hammerheads grow up to 10 feet long and have indentations in their flat, extended heads. They eat stingrays, squid and other sharks.

They're the most commonly found hammerhead species in Hawaii where they're better off in Hawaii than elsewhere because there's no traditional or modern market for sharks as a commercial species in the islands, said Kim Holland, also a researcher at the Hawaii Institute for Marine Biology.

The Associated Press