In this undated photo, a porpoise is seen trapped in a fishing net at the Gulf of California. (C. Faesi/Proyecto Vaquita via AP)

Little is known about the shy vaquita porpoises that spend long periods feeding under muddy coastal waters off Mexico, but this much is certain: They are the world’s smallest porpoise — cute as a button — and they could soon disappear forever if they keep turning up dead in fishing nets.

The latest stock assessment by a panel of international scientists showed that there are fewer than 100 left and that they are declining at a rate of nearly 20 percent a year. U.S. officials have pressed Mexico to close their habitat in the upper Gulf of California to all fishing, and they expressed exasperation recently when the Mexican government did not announce stricter regulations as expected.

If vaquitas vanish, they would be the first known cetacea in North America to do so and the first in the world since the Chinese river dolphin was declared extinct in 2006.

Dolphins differ from porpoises in their noses, namely that blunt-faced porpoises do not have much of a snout. But the vaquita overcomes that shortcoming with a starlet’s beauty. “It’s got the goth look going on, the black lipstick and heavy mascara around the eyes,” said Barbara Taylor, a conservation biologist for the Southwest Fisheries Science Center, run by the U.S. Commerce Department in San Diego.

Timid and elusive, vaquitas — Spanish for “little cows” — are four to five feet long and weigh up to about 120 pounds. They get caught in the gill nets of Mexican fishermen casting for large blue shrimp, a delicacy American restaurant-goers crave.

They also drown in the nets of poachers in pursuit of the endangered totoaba, a large sea bass prized for its bladder, which is cherished by the Chinese as an alternative medicine. A pair of totoaba bladders can fetch $8,500 in China, officials with the National Marine Fisheries Service said. In recent weeks, 385 bladders were confiscated in Mexico City.

To rescue vaquitas, international scientists are hoping for a collaboration between the United States, where the shrimp is consumed; China, where the bladders are boiled into a soup; and Mexico, where fishermen are trying to feed families.

Mexico passed laws that would gradually replace mesh gill nets that snare the animals with a baglike trawl made of lightweight material, but U.S. officials said that the three-year transition could be fatal for an animal predicted to disappear altogether in four years.

“Saving the vaquita is a priority for the Mexican government,” Mario Aguilar, head of Mexico’s National Commission of Aquaculture and Fishing, told U-T San Diego in August.

Aguilar said then that the government had recently received a report from an international panel that estimated the vaquita population at 95 and listed its prospects as dire.

Taylor and scientists at the federal Marine Mammal Commission said paying fishermen to stop using gill nets is one option, and Aguilar said Mexico was exploring the idea of buying trawls that cost between $1,000 and $5,000.

“We’ve got to recognize that this is an issue that is going to require some resources,” Aguilar told U-T. “Don’t forget that there are 30,000 families that are going to have to find a different way of life.”

Vaquita is seen caught as by-catch in Baja California, Mexico. (Flip Nicklin/Minden Pictures via Getty Images)

U.S. officials expected an announcement that never came in late November, and they say they are desperate to find a solution before it’s too late.

“Lack of enforcement of existing [Mexican] laws is a very serious issue,” Taylor said. “The type of net used to catch totoaba is illegal. Boats out there don’t have permits. The fishermen themselves are vocal about the need for enforcement. Not only have we not seen any improvement, things have gotten worse — significantly worse.”

“Of course there’s this reality of losing an animal forever,” said Frances Gulland, a commissioner of the Marine Mammal Commission. “It’s not a sea cucumber. It’s a charismatic, cute animal that anyone who sees it can identify with.”

Solutions such as closing parts of the gulf or eliminating gill nets do “impact fishermen in the area and the community,” Gulland said, but they should not be so hard to implement. “We have this ability to be creative and go to the moon, but we can’t solve this difficult problem.”

The upper Gulf of California near the Colorado River delta is the endangered vaquita’s only habitat. There’s a theory of how it got there: The vaquita’s closest relative is the Burmeister’s porpoise, thousands of miles south in Peru. A group of Burmeister’s porpoises might have swum to the gulf thousands of years ago and were somehow isolated and could not return. Stranded along two muddy coasts, they used echolocation to fish for squid, octopuses, crustaceans and croaker.

Scientists did not know the vaquita porpoise existed until a few skulls were discovered in the early 1950s. About 25 years later, they were classified as a vulnerable species by the International Union for the Conservation of Nature, said Randall Reeves, who chairs the scientific advisers committee for the Marine Mammal Commission.

In 1985, they were placed on the U.S. Endangered Species List. Five years later, they were entered on the international union’s red list of endangered animals, and a year later, the species was bumped up to a critically endangered declaration.

The plight of vaquitas mirrors that of the totoaba. In a frenzy of fishing in 1942, Mexicans caught more than 2,000 tons of the fish, also probably pulling up drowned vaquitas in nets that lingered in the water.

When the totoaba fishery produced only 59 tons in 1975, strict regulations were put in place. Two years later, vaquitas were listed as threatened. A quick recovery for the remaining 100 is not likely, biologists say. They mature at 3 to 6 years of age, and females give birth to a single calf every other year.

To grasp “how big a shocker” their extinction would be, Taylor said, think about the vast slaughter of whales in the 19th and 20th centuries. “Despite all that effort, humans didn’t drive any of them to extinction. Most of those species are recovering.

“But the ones really in danger are these small dolphins and porpoises that live only where humans live. And if we don’t solve this, we’re going to lose species after species.”