The National Marine Fisheries Service on Thursday classified as endangered and threatened four distinct 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 southwest 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 Hawaii 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, 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.

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. They give birth in calm, murky, shallow bays, including Kane­ohe and Pearl Harbor on Oahu, Hanalei on Kauai and Hilo on Hawaii island.

They’re better off in Hawaii than other areas in part 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.

Studies indicate the Hawaii population stays in waters relatively close to shore, which may give them some additional protection. That’s because longline fishing fleets can accidentally catch the species, but the Hawaii-based fleet fishes farther from the coast.

By Audrey McAvoy, Associated Press