Biologists say that for the vaquita of the Gulf of California, a small species of porpoise and the rarest cetacean in the world, extinction is just four years away.

In reaction to the increasingly dire situation -- at last count, there were less than 100 specimens -- conservationists recently penned a strongly worded letter to Mexican President Enrique Pena Nieto. The groups threatened to pursue a variety of trade-based actions against Mexico and its fishing industry, should the government fail to up its efforts to protect the vaquitas.

The letter -- signed by American Cetacean Society, the Center for Biological Diversity and the International Fund for Animal Welfare, among others -- warned that activists in the United States were petitioning the Obama administration to enforce a provision of the U.S Marine Mammal Protection Act that could ban Mexican shrimp imports.

Environmental groups are also pressuring the White House to foist trade sanctions upon Mexico for failing to enforce an international ban on illegal totoaba fishing.

The illegal use of massive gillnets by Mexican fisherman in the Gulf of California (also known as the Sea of Cortez) is widely blamed for the vaquitas' dwindling numbers.

According to a new study by the International Union for Conservation of Nature, at least 90 fishing boats have been spotted fishing in an area critical to the endangered vaquita. At least 17 of those boats have been confirmed to be using gill nets.

"Time is running out," Rebecca Lent, executive director of the Marine Mammal Commission, told the Los Angeles Times. "The government of Mexico has made an effort, but it has been ineffective. What we need is a firm commitment by Mexico to stop the gillnetting. Now."

The Marine Mammal Commission is an independent federal agency tasked with reviewing federal policies and making amendment recommendations to the National Oceanic and Atmospheric Administration.

Officials in Mexico say they want to conduct another study to count the vaquita.

"We don't need another study," Lent said. "The best scientists in the world have already looked at the data and concluded that the decline of the vaquita has accelerated because of unregulated gillnetting."

"The vaquita," Lent told the L.A. Times, "may go extinct in 2018 -- just six decades after it was discovered."