MEXICO CITY (AP) — Mexico enacted a permanent ban on gillnet fishing in the northern Gulf of California on Friday in a bid to protect the critically endangered porpoise known as the vaquita marina.

The measure, which makes permanent a temporary ban in place since April 2015, is the first step toward fulfilling an agreement reached this month by President Enrique Pena Nieto and the foundations of actor Leonardo DiCaprio and telecom billionaire Carlos Slim to try to save the vaquita.

The diminutive vaquita is the world's smallest and most endangered marine mammal, with only about two-dozen remaining in their habitat in the upper Gulf.

Their numbers have been greatly reduced in recent decades by the illegal use of gillnets, which are primarily used to catch the totoaba fish but can ensnare and kill vaquitas as well.

The World Wildlife Fund issued a statement supporting the ban.

"This is a fantastic and encouraging step forward in the path to saving the vaquita, provided the ban is fully enforced and accompanied by fishing alternatives for local communities," acting CEO Jorge Rickards was quoted as saying.

Despite authorities' oft-expressed commitment to saving the vaquita, enforcement has not been entirely effective. The swim bladder of the totoaba is prized in China and can sell for huge sums, offering a powerful financial incentive for fishermen to pursue that catch at the vaquita's expense.

The newly permanent measure provides for monitoring in the region especially for fishing vessels and landing sites. It will be illegal to transport gillnets into the area, and fishermen will be required to report any lost gear to avoid harming the delicate ecosystem.

Mexico is the first country to enact such a ban on gillnets, also known as ghost nets due to their invisibility to marine mammals.

"Great news as the permanent ban on gillnets has been made official," DiCaprio said in a Twitter message that was retweeted by Pena Nieto.