A judge has ordered the U.S. government to ban imports of seafood caught by Mexican fisheries that use a net blamed for killing off the vaquita, the world's smallest and most-endangered porpoise.

Judge Gary Katzmann, of The U.S. Court of International Trade, on Thursday granted a motion after three environmental groups filed a lawsuit seeking a ban on seafood caught with gillnets in part of the Gulf of California, where the vaquita live.

Some scientists estimate that there could be as few as 15 of the vaquita — Spanish for "little cow" — left. The court noted that experts believe they could be extinct by 2021 without intervention.

Their numbers have been severely reduced illegal fishing and by the gillnets, which are used to catch a variety of shrimp and fish.

The nets are hung in the water to catch seafood. The Mexican government has banned their use in some areas and for some species, but allows it for other species.

There also is illegal fishing in the vaquitas habitat for the Mexican totoaba fish, which goes for high prices because its swim bladder is considered a delicacy in China and reputed to boost fertility.

The Justice Department, which had opposed the ban, did not immediately answer an email seeking comment.

The groups that filed the suit are the Natural Resources Defense Council, the Center for Biological Diversity and the Animal Welfare Institute.