American Samoa is banning shark fishing in its waters in hopes of stopping the population's decline.
It is among a number of Pacific islands to record a dramatic drop in shark numbers.
Sharks are often harvested for their fins, which typically end up in restaurants as shark-fin soup.
The rules taking effect this week make it illegal to catch or possess sharks within three nautical miles of the shoreline. The ban extends to three species of reef fish.
Doug Fenner, who monitors sharks for the Department of Marine and Wildlife Resources, says the rules cover most of the territory's coral reefs and will prevent shark trafficking.
Mr Fenner said the protections are the most powerful in the US. American Samoa is an unincorporated US territory.