Mexico's President Enrique Pena Nieto wrote to Leonardo DiCaprio on Twitter on Thursday in a bid to reassure the Hollywood actor his government was taking steps to protect a rare porpoise in Mexican waters teetering on the brink of extinction.

Populations of the vaquita, a tiny snub-nosed porpoise that lives in the Gulf of California, have dropped sharply in recent years because of gillnet fishing for shrimp and totoaba, a popular delicacy in Asia, sparking increased international concern.

The vaquita is the most endangered marine mammal in the world. Join me + @World_Wildlife and take action. https://t.co/sB80PCeTG9 pic.twitter.com/UQMomVkvlC

— Leonardo DiCaprio (@LeoDiCaprio) May 11, 2017

On Wednesday, DiCaprio called on his 17.5 million Twitter followers to get behind a World Wildlife Fund campaign online, which urged people to petition the Mexican president to "take strong action now" to save the vaquita.

On Thursday evening, Pena Nieto took to Twitter in English to defend his government's efforts on behalf of the vaquita, addressing the actor directly with his first tweet.

I welcome @LeoDiCaprio and @World_Wildlife 's concern regarding the Vaquita Marina.

— Enrique Peña Nieto (@EPN) May 12, 2017

.@Mexico has focused all its efforts to prevent the extinction of this species.

— Enrique Peña Nieto (@EPN) May 12, 2017

"I welcome @LeoDiCaprio and @World_Wildlife's concern regarding the Vaquita Marina," Pena Nieto wrote. "@Mexico has focused all its efforts to prevent the extinction of this species," he said before sending out five more tweets, all in English, to draw attention to what Mexico is doing.

Since Feb/2015, we have eliminated one of its main causes of death: the shrimp and scale fishery, establishing a two-year ban on the area.

— Enrique Peña Nieto (@EPN) May 12, 2017

Mexico's government is making a major effort, doing what should have been done decades ago to save the Vaquita Marina.

— Enrique Peña Nieto (@EPN) May 12, 2017

Mexico imposed a two-year ban on gillnet fishing in the vaquita's habitat in 2015, extending it earlier this year. Critics have complained the ban needs better enforcement.

Viva Vaquita, a group dedicated to saving the porpoise, says on its website that the vaquita population was estimated to be less than 50 in January 2017, based on earlier study findings.