Regulators are tightening restrictions on the last species of shark whose fins can be removed at sea by fishermen in the U.S.

Smooth dogfish are the only sharks from which American fishermen can remove fins at sea. Many other sharks can be hunted, but fins can’t be removed until the sharks are processed on land.

The Atlantic States Marine Fisheries Commission voted Tuesday to approve a rule that allows fishermen to bring smooth dogfish to land with fins removed, as long as their total retained catch is at least 25 percent smooth dogfish. Right now, they can bring ashore as many as they want.

The rule change better incorporates the Shark Conservation Act of 2010 into management of the dogfish, said the staff with the fisheries commission. The dogfish are harvested from Rhode Island to North Carolina, and are among the many shark species that fishermen bring to land in states from Maine to Texas.

Sharks are also hunted for their meat, but their greatest value is in their fins, which are used to make shark fin soup.

“The fins are worth more than the meat,” said Ashton Harp, a fishery management plan coordinator with the commission.

One reason smooth dogfish fins can be removed at sea is that the dogfish are prone to spoilage, Harp said.

Some environmental groups want to shut down the U.S. shark fin market. They have supported legislation pending in Congress that would come close to doing that.

The conservationist group Oceana has argued that allowing fin removal bolsters the global shark fin trade, which leads to the practice of “finning,” cutting the fins off live sharks and dumping the animals back in the water. “Finning” is illegal in the U.S.

Lora Snyder, the group’s responsible-fishing campaign director, called the new dogfish rules a step in the right direction but said the changes don’t go far enough because it will still be legal to remove fins from sharks.

“As long as there is market demand for shark fins, finning is a potential threat to all shark species, including smooth dogfish sharks,” she said.