Scientists feared they were on a grim mission. Biologists searching Mexico's Sea of Cortez for the world's most endangered marine mammal—a tiny porpoise called the vaquita—worried they might already be too late.

As few as 97 vaquitas remained on Earth last year. With poachers and fishermen accidentally snaring them in nets, scientists suspected this elusive creature’s race to extinction might have accelerated.

Yet last week, while cruising through glassy water on a research boat off Baja California, the world’s leading vaquita experts from the United States and Mexico spotted first one, then another, through binoculars. A few days later, several of the shy mammals were seen once again. There could be no doubt.

"It was incredible; people were jumping up and down," Barbara Taylor, a marine biologist with the National Oceanic and Atmospheric Administration and the chief U.S. scientist, said via satellite phone from the vessel. "A decade ago this would have been routine. On this trip, it was just such a relief. It was joyous."

Says Chief Mexican Scientist Lorenzo Rojas-Bracho: "It was so good to see the animals are still there. They're still in big trouble. But this gives us hope."

'It's Been So Frustrating'

Vaquitas are only found in a northern stretch of inland sea off the Baja Peninsula, giving them the smallest range of any marine cetacean. They can weigh 65 pounds—little more than a child—or up to about 120 pounds, and stretch only four or five feet long. The world’s smallest cetaceans, they are noted for their unusually stubby snouts and striking dark areas around their eyes and lips.

View Images Vaquitas like this one are often killed when they are snared in gillnets used to gather shrimp and fish. Photograph by Flip Nicklen, Minden Pictures/National Geographic

Scientists have only known of the vaquita's existence since 1958, when three small skulls were found on a beach. Even then, they were so rarely seen that many people in and around Mexico refused to believe they were anything more than a myth.

By the early 1970s it was clear that the vaquita was in decline. They drowned in nets as the fishing industry chased totoaba, a critically endangered fish whose swim bladder was considered a delicacy in Asia. Totoaba fishing was banned in the mid-1970s. Yet by the 1990s, vaquitas were still disappearing as netting for shrimp and other fish continued.

The Mexican government created a refuge for vaquitas in the mid-2000s. It spent millions of dollars buying out gillnet fishers and urging them to switch to less damaging fishing gear. Still fishing continued, and porpoise numbers dropped. "It's been so frustrating," says Rojas-Bracho. "First there's less than 600, then the next survey it's 205. And it just keeps going down."

Then, just as the situation seemed critical, a new crisis emerged.

Trying to Avert Extinction

By 2010, as Chinese wealth continued its surge, the market for totoaba swim bladders roared back. Suddenly these dried bladders could fetch tens of thousands of dollars on the black market. Mexican drug cartels got in on the action.

In the 1970s, prices for totoaba were low. The new sky-high market “was a complete game-changer," Taylor says. Taylor was told that totoaba bladders were so hot that they could be purchased and stored in a safe in China and held like a precious metal. "They were more stable than gold," she says.

The Mexican government helped scientists set up underwater acoustic monitoring to track vaquitas. Researchers learned the population had plummeted as much as 42 percent, just between 2013 and 2014. "That," Taylor says, "was sobering."

Earlier this year, in a last-ditch effort to stave off extinction, the Mexican government took the unusual step of instituting an emergency two-year ban on all gillnets, the first of its kind anywhere in the world, Taylor says. During previous surveys in 1997 and 2008, "we saw hundreds of boats and about 700 kilometers of net in the water," Taylor says. "This time we saw none." The Mexican Navy made strides in arresting poachers.

Rojas-Bracho hopes the fact that vaquitas are still visible will convince Mexico’s government to make the temporary gillnet ban permanent. During a trip last week, top Mexico officials saw vaquitas for the first time. Scientists said spying the timid creatures first-hand left a huge impression.

Taylor, for one, is grateful vaquitas have any chance at all. She’s seen things go the other way. Taylor and two others on the research cruise in Mexico were part of a 2006 survey in China, where they’d hoped to rescue the last remaining endangered Yangtze River dolphins and place them in captivity to keep that species alive. By the time they arrived the last dolphins had vanished.

"That was an incredibly depressing experience," Taylor recalls. "Here was a species that had been on the planet for 20 to 30 million years, and just like that it was gone. We came back determined to keep our eye on the ball. We weren't going to let that happen again."

Even though vaquitas now number in the dozens, Taylor and Rojas-Bracho say recovery remains possible. For evidence they point to nearby Guadalupe Island, where Guadalupe fur seals were brought back from the brink of extinction and now number in the tens of thousands. Still, the road to recovery for this pint-sized porpoise is long.

"It's way too early to say what's going on," Taylor says."But the habitat is healthy. I can look out a porthole right now and see this gorgeous sea with plenty of fish surrounded by austere desert.

“It would be criminal to lose this species,” she adds. “There's nothing to prevent these animals from recovering if we just stop killing them."