What It Takes to Save the Axolotl

Xochimilco is a large, semirural district in the south of Mexico City, home to a vast network of canals surrounding farming plots called chinampas. Starting around A.D. 900, this maze of earth and water produced food for the Xochimilcas, a Náhuatl speaking people who were among the first to populate the region and engineer its wetlands.

Nowadays in the early mornings, farmers — many of them descendants of Xochimilco’s original inhabitants — can be seen loading canoes with lettuces and flowers grown in the rich sediments dredged from the canals. On weekends, hundreds of brightly colored party boats crowd the waters, full of urbanites seeking escape.

The Mexican axolotl — a dusky amphibian with the remarkable habit of neoteny, or retaining its juvenile body type all its life — once thrived in these canals. Though axolotls have been reproduced widely as lab animals and in the aquarium trade, where they are more often pink or yellow thanks to genetic mutations, it is now questionable whether any significant wild population remains. At last count, a decade ago, there were 35 axolotls per square kilometer in the Xochimilco wetlands, down from thousands in the 1990s. Pollution, urbanization and introduced fish species had made life nearly impossible for them.

In the early 2000s, Luis Zambrano, an ecologist at the National Autonomous University of Mexico, or UNAM, was studying the effects of invasive carp when he was tapped by the government to survey axolotls. After decades of steady environmental degradation in Xochimilco, Mexico wanted to know how many axolotls remained in the species’ last stronghold. Axolotls were of deep cultural importance, a feature of the region’s traditional diet and cosmology. And laboratory biologists all over the world, who for more than a century had used axolotls to study tissue regeneration, worried that their animals were becoming inbred, without a wild population from which to draw new bloodlines.

As an ecologist, Zambrano never entertained any strategy to save the axolotl that did not involve first restoring its habitat. But “this isn’t the middle of Borneo or the great plains of the Serengeti,” he said. The habitat was Mexico City, population 22 million and growing. The number of factors counting against success was staggering.

Springs that historically fed the Xochimilco wetlands were long ago diverted for urban use, replaced by treated wastewater. Introduced carp and tilapia ate axolotl eggs. New roads pushed urbanization ever further south, threatening the last remnants of the unique pre-Columbian farming culture whose canals had sheltered axolotls for over a millennium. Party boats not only brought noise and more pollution but tempted farmers to convert their chinampas to restaurants, bars and soccer fields and to let small canals dry up.

Representations of axolotls occur everywhere in Mexico City — their enigmatic faces grace street murals, handicrafts and even, lately, a 50-peso bill — but the animal’s natural history is unknown. Nearly everything that has been learned about axolotls comes from specimens in tanks.

The only way to save and study the wild axolotl, Dr. Zambrano and his colleagues determined, was to promote a renaissance of ancestral farming practices, and then convert segments of the farmers’ canals into axolotl sanctuaries, with the hope that one day they could be linked together. For more than a decade Dr. Zambrano and his colleagues have published extensively on the philosophy and logistics of this approach. A major conservation group now backs their efforts, while some of their fellow axolotl researchers find them to be borderline quixotic.

Now Dr. Zambrano and his team have put their ideas to the test with the release of a small number of animals. Twelve, to be exact.

‘How’s the oxygen?’

Axolotls must be kept cool, and Dr. Zambrano’s lab at UNAM, home to a breeding colony of about 150 animals from wild bloodlines, is maintained at 64 degrees Fahrenheit. On a mid-October morning, with his colleague Carlos Sumano navigating, Dr. Zambrano and a cadre of students set out in a flat canal boat with six lab-reared animals in coolers. All were spry yearlings; under the right conditions, axolotls can live to age 20.

In 2017, Dr. Zambrano’s group radio-tagged 10 axolotls and released them into an artificial lake on the UNAM campus. They saw that the amphibians, not thought to be especially social, often got together in the afternoons for an hour or so and then dispersed. They observed a male and a female that never strayed more than a few feet apart. They also saw one end up in the stomach of a water snake. But the animals gained weight — they had no issue finding food.

The axolotls on that October day would be released in submersible cages of bamboo and shrimp netting, allowing them to move around and hunt without being preyed on. The cages would go into canals fitted with biofilters, made of volcanic rock and native plants, to keep out pollutants and invasive fish. Each canal had to be cool and oxygenated and had to contain plenty of tiny crustaceans for the axolotls to eat. Just six animals were being released, into two canals. In a week, the group would release another six. Even thinking about reproduction was too much for now: The animals were being segregated by sex. It was enough if they survived.

María Huitzil, a doctoral student at Metropolitan Autonomous University in Xochimilco, was working on a study that piggybacked on Dr. Zambrano’s and his colleagues’ conservation effort. She planned to retrieve the axolotls monthly and swab their skins for “bacteria, fungi, viruses, all the eukaryotes and prokaryotes that have important functions in nutrition, osmoregulation, nutrition and defense,” she said. With most of the world’s axolotls reared in fish tanks, no one really knew what their natural microbiota consisted of. Yet they seemed to resist the infectious chytrid fungus, which has wreaked havoc on amphibian populations worldwide. What other secrets would the skin swabs reveal?

With the boat tied up, the students moved ashore at their first chinampa, a bustling vegetable farm with rows of sunflowers, corn, greens and tomatoes. Javier del Valle, a co-owner and a fourth-generation chinampero, watched as Dr. Zambrano and Mr. Sumano dug a ledge into the black soils of his canal’s banks and began sinking one of their unwieldy, six-foot-tall bamboo cages into it. The students dipped their instruments to measure dissolved oxygen, turbidity and conductivity. “How’s the oxygen?” Dr. Zambrano wanted to know.

A Xochimilco native, Mr. del Valle had grown up eating axolotls, mostly in the form of tlapiques, tamales combining fish, amphibians and vegetables from the chinampas. Unlike many of his neighbors, who have converted their plots to other uses, he believes in the virtues of traditional chinampa farming, which uses no chemical pesticides or fertilizers. He and his family grow 80 varieties of flowers and vegetables on their chinampa, including a rare red spinach that he plucked for the team to sample.

His axolotl refuge, at first glance little more than a ditch, had taken five years to set up. The UNAM researchers supplied a 70-page manual to interested farmers that described how the canals should be built. “These are small steps, right?” said Mr. del Valle, a Náhuatl speaker who can recite the harvest festival dates for every crop. “But it is a very titanic task.” To him, conserving axolotls on his chinampa was part of a more ambitious goal. “It’s about returning to a certain knowledge, a certain time,” he said.

“Chinampaneros like Javier are an endangered species, too,” said Ms. Huitzil, the doctoral student.

By noon, the researchers finally had their cage stabilized in the canal, ready for the animals. The canal’s oxygen levels weren’t great, but Dr. Zambrano decided it didn’t matter. It was important to know whether axolotls could survive in suboptimal conditions, so long as predators and toxins were kept at bay.

An advantage of placing only a few animals into isolated canals was that it allowed for failure here and there. Risking too many animals at once was reckless. Only last year, local politicians released 200 captive-raised axolotls into a polluted canal, for a media stunt that most likely ended with all of them dying.

The students removed three wriggling females from bags in the coolers and then lowered them into their new, semi-wild home. They sealed the top of the cage, which poked above the surface. Dr. Zambrano stood staring at it for a while without speaking. “That’s it,” he said nervously, to no one in particular.

Officially, the Mexican government has long agreed that this habitat should be conserved. The Xochimilco wetlands were designated a UNESCO World Heritage site in 1987; five years later, the entire system was designated a protected natural area. None of it has kept axolotl numbers from plummeting.

Legally, no houses or permanent structures can be built on chinampas; farmers like Javier del Valle commute to them by canoe. Yet every day boats can be seen carrying building materials. Internal migration puts pressure on any cheap land with access to Mexico City, with which Xochimilco is ever more integrated. In 2020, builders began filling part of its wetlands for a new highway bridge, prompting a lawsuit and fierce protests by environmentalists. The bridge went up anyway, and Dr. Zambrano described the episode as one of the rare moments over the past 20 years in which had he considered throwing in the towel. “I mean, it was our own government doing this to us,” he said.

Another group of axolotl researchers in Xochimilco maintains a breeding colony, derived from three dozen wild individuals, that precedes Dr. Zambrano’s involvement with the species.

The campus of the Centro de Investigaciones Biológicas y Acuícolas de Cuemanco, or CIBAC, sits just a few hundred feet from the UNAM field site in Xochimilco. Its director, José Antonio Ocampo, explained in a recent visit that while the axolotls bred there are healthy and genetically robust, CIBAC has not attempted to release any since 2013. Conditions are simply too terrible.

Dr. Ocampo, whose background is in aquaculture, said he agreed with the UNAM researchers that the conversion of chinampas to other uses was among the gravest threats to the species. But if you don’t provide chinamperos with constant financial support, it’s hard to keep them committed, Dr. Ocampo said. “So the idea is to look for places where we don’t have to depend on that.”

Dr. Ocampo and his colleagues have been focusing on a lake that sits within a government-run nature park in Xochimilco. The lake is cleaner than the main canals, the researchers determined, and can be more easily policed. Preliminary studies are underway for a release in two years.

Conservation International, the large environmental nonprofit, is backing Dr. Zambrano and his group’s plodding, chinampa-centric approach. The organization recently secured for the group a multiyear grant funded by Microsoft Corporation, which sponsors global water-replenishment projects to help compensate for the water used in its operations. The UNAM program, which cleans canal water with biofilters, fit the bill perfectly, said Esther Quintero, a biologist and the technical director for Conservation International in Mexico.

“You cannot think about saving a species without saving the habitat,” Dr. Quintero said. And habitat restoration “is a marathon, not a sprint. It can take a generation or more to see results.”

In a country like Mexico, Dr. Quintero stressed, you can have all the laws you want on paper, but the only conservation strategies that work are practical ones that put people at their center. “Here you cannot conserve anything if you’re not going to use it at the same time,” she said. “Under this model, you’re using the soil, you’re using the land, and by using it properly you’re conserving an ecosystem in which the axolotl co-evolved.”

Axolotl adoption

Most members of Dr. Zambrano’s team work at the lab on the UNAM campus, but one, Mr. Sumano, an agronomist, lives and works in Xochimilco.

Over his 11 years there, Mr. Sumano has seen countless chinampas repurposed as businesses catering to the party boat crowd; one now boasts a Texas-style barbecue with picnic tables. Several are home to “ajolotarios” — little bar-zoos where, for a small fee, you can view hundreds of axolotls in tanks, most of them the candy-colored products of commercial breeding.

Mr. Sumano’s efforts to persuade more chinamperos to resume ancestral farming led him to buy his own chinampa and farm it. He has helped about 20 families set aside the pesticides and other chemicals they were accustomed to using, and which they sometimes received free from the government. Mr. del Valle and his brother, he said, were among the first who were willing to give the program a try.

Still, 20 families represent only a fraction of Xochimilco’s registered chinampa farmers. Uptake is slow, Mr. Sumano acknowledged. Farmers can’t simply be told that their harvests will improve. They need to see it for themselves, and that takes time and close collaboration. Building an axolotl refuge is another exacting process; just getting the canal dug can take 10 men a full month. Mr. Sumano makes it his business to always be available to farmers, absorb any complaints and make sure they get the modest funds promised to them for participating.

Mr. Sumano and Miguel Ignacio Rivas, a biologist with Dr. Zambrano’s group, have endeavored to make traditional practices profitable for chinamperos, through a produce certification program and engaging a culinary school to plug the virtues of chinampa-grown vegetables. An “adopt an axolotl” campaign, run by a graduate student, Diana Vázquez, raises funds and helps explain, in lay terms, how the group’s programs work.

For these researchers, the effort is about far more than the axolotl. It’s about reconnecting axolotls with their natural habitat in the public mind, and learning to value a wetland farming system that has been wrongly maligned as backward. “The chinampas capture an incredible amount of carbon,” offering an important hedge against climate change, Mr. Sumano said. “I don’t know what ramifications that their disappearance could have, both environmental and social.”

As Mr. Sumano spoke, a group of his students was building more axolotl cages on the lawn of UNAM’s field site in Xochimilco, getting ready for the next day’s releases. In these clean canals full of crustaceans and water plants they liked, the axolotls would gain weight fast, Mr. Sumano predicted.

Nearly two months later, one of the 12 had died, of causes yet to be determined, and a pump had to be installed to improve oxygen levels in one canal. “But that’s all part of the experiment, right?” Dr. Zambrano said. The rest of the axolotls were fat and happy.