PORTLAND, Maine (AP) — Interstate regulators are tightening the restrictions on the last species of shark that can have its fins removed at sea 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 processing on land.

The Atlantic States Marine Fisheries Commission voted Tuesday to approve a new 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 choose.

The rule change would better incorporate the Shark Conservation Act of 2010 into management of the dogfish, staff with the fisheries commission said. 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 of the reasons smooth dogfish can have fins removed at sea when other sharks can’t is because the dogfish are prone to spoilage, Harp said.

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

Conservationist group Oceana has argued that allowing legal fin removal bolsters the global shark fin trade, which leads to the practice of “finning,” or cutting the fin off a live shark and dumping the animal back in the water, in other countries. “Finning” is illegal in the U.S.

Oceana responsible fishing campaign director Lora Snyder called the new dogfish rules a step in the right direction but also 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.