Rewilding the Axolotl

The darkness of night has given up to the soft haze of dawn. I’m arriving at a pinned location of coordinates in what some might call the middle of nowhere, following them like one might play a game of Hot and Cold until I see a small shack in the distance. The cacophonous morning greetings of birds in the canopies above me take over the sounds of frogs and crickets on the forest floor below me. As I walk toward the shack, a figure comes out and meets me halfway. 

Carlos Uriel Sumano, a tall, scruffy 38-year-old wearing cargo pants and a worn cotton long sleeve, greets me as he gestures to follow him to the shack that has the words “MONITORING STATION UNAM” spray-painted at the entrance. Next to the words, warping up and down with the grooved plastic siding, is the portrait of a flat-faced creature with protruding eyes and what looks like the collar of a medieval jester. Sumano, putting on a sun hat while gathering supplies, asks me, “So, what do you want to know?” to which I reply, “Everything.” 

I’m an hour drive south of the bustling center of Mexico City, a welcome escape from the boisterous city life. Today, I’m joining Sumano on a scientific expedition. He’s the lead on a team of agricultural scientists at the National Autonomous University of Mexico in Mexico City (UNAM) that is tasked with the elaborate effort of rewilding that flat-faced, googly-eyed creature in the spray painting: the axolotl. The axolotl is a critically endangered aquatic salamander that’s native to only Lake Xochimilco, where I’m currently visiting Sumano. (All interviews were conducted in Spanish.)

Rewilding is the process of restoring an ecosystem to its natural, uncultivated state. A progressive approach to conservation, it ensures a healthy future where nature can once again take care of itself as it did before human intervention versus a future where a species is preserved in a zoo or lab. In the case of the axolotl, it is a process that can take up to three years, depending on what steps need to be taken in its selected sanctuary in the lake.

Seen from a bird’s eye view, the lake resembles more of a jigsaw puzzle: chunks of land with streams of water snaking through, dividing the pieces. Now the Xochimilco canals, this area exists as the only remaining part of a much-larger lake system that was eventually drained by the Mexican government to reduce flooding. Mostly known for its party boats called trajineras in Spanish, Lake Xochimilco is where foreigners and locals alike gather to celebrate birthdays or have a fun, booze-filled day with friends as they drift on the lake’s canals. The flat-bottomed wood boats are brightly painted and named after loved ones or Mexican phrases. 

However, long before the party boats, Xochimilco was home to Mesoamerican cultures, including the Aztecs, who made it the agricultural center of their empire. The Aztecs created those puzzle pieces, called chinampas, which are nutrient-rich agricultural islands with complex drainage systems. These highly functioning agricultural oases were created by layering different types of sediment and outlining them with ahuejotes, native willow trees whose roots grounded the island into the earth. With information transmitted through oral knowledge since the Aztecs, they are still in use today by chinamperos, or farmers who use chinampas.

The crops from chinampas provide fresh produce to much of Mexico City’s inhabitants, the same way they did over half a millennia ago for the Aztecs. The canals that snake through them are their roads, creating a water city reminiscent of Venice—if you just replace stone and gondolas with prehistoric wetlands and canoes. In 1984, the area was declared a biological reserve and, three years later, became a UNESCO World Heritage site. A whopping 11% of the entire country’s biodiversity can be found in this 470-acre wetland. 

One of the animals included in that percentage is the peculiar axolotl, or Ambystoma mexicanum, whose only home in the wild has been Lake Xochimilco. 

Physically, the creature’s feathery external gills, tadpole-like tail, and perma-smile can’t help but make it adored by everyone who encounters it. Through a phenomenon called neoteny, it remains a juvenile forever (at least physiologically) while having the ability to reproduce. While its seclusion in a high-altitude body of water could play a factor as these conditions are understood to favor neoteny, scientists don’t know for certain how the axolotl evolved or why it doesn’t metamorphosize and migrate to land like its salamander relatives.

This phenomenon is only one among many remarkable abilities that make the axolotl valued by scientists worldwide. Perhaps one of the most impressive and mystifying of those abilities is its capacity to regrow limbs, organs, and parts of its eyes and brain. These animals are incredibly resistant to cancer, grow stem cells their whole life, and have a genome 10 times the size of humans. They are, quite simply, imperative to studies in the fields of science and medicine. Due to habitat degradation and water contamination (among other factors), they are also critically endangered in the wild—with an estimated 50 to 1,000 left. 

Behind the chaos of trajineras and mariachis, roughly 100 miles of pre-Hispanic canals delicately reside where Indigenous farmers and scientists are working to preserve an animal, as well as a culture that itself is endangered. Sumano works with certain chinamperos to rebuild the axolotl’s habitat within the smaller canals on the islands that are more effective in keeping the axolotl safe. 

Sumano is packing a canoe in a small inlet behind the shack with his assistant before we set off in two canoes, entering the larger 200-foot wide canals. It’s bright now, and we’re saying good morning to passersby on other boats while several bird species compete with each other in a symphony of their respective chirps, whistles, and croaks. There are over 120 species of birds that call Xochimilco home including herons, kingfishers, and black ibis. Our first stop is the chinampa of José de La Cruz. Sumano is here to check the state of the water in the canals his team has started reconstructing that will hopefully house future axolotls. 

We pull over on the side of the island and hop onto dry land, making our way through small crop fields. When we find Señor de La Cruz, he seems concerned about the water: it’s brown and lower than usual. Mexico City is in the thick of its dry season, and rain hasn’t fallen for weeks. Sumano walks along a single wooden plank, pausing in the middle of the small canal, and intrepidly reaches his hand into the murky water, pulling out a slew of plants. The roots are muddy. One might think this is perfectly normal, but to Sumano and the team, it’s not. By now, the water should be self cleaning. Sumano and his team have concluded that the water must be getting contaminated from the neighboring chinampas that have transformed into football fields.

De La Cruz shares how his family has had this chinampa for four generations and the importance of continuing this tradition. Sadly, many chinamperos have broken tradition by expanding their islands into larger agricultural operations as they can make more money this way. This brings more people into the reserve to sell and consume goods, which means more trash and runoff into the lake’s already fragile ecosystem. 

“The health of our water depends on our own health,” De La Cruz recounts as Sumano is reviewing next steps with his team. He believes, like many other locals, that the survival of the axolotl is equal to his own survival. 

The axolotl is not only valued by the science community; it is a cultural icon to its home country. The creatures are even pictured on the new 50 peso note. The Aztecs thought them to be the reincarnation of the Aztec god Xolotl, which loosely translates to water monster. The twin of Quetzalcoatl, he was the deity of fire and lightning and believed to transform into an axolotl in order to escape being sacrificed. For this, he was condemned to the depths of Xochimilco—left neither animal nor human, but the creation of a fallen god. 

While centuries have come and gone and stories have endured, the axolotl has remained a beloved cultural centerpiece for Mexico. It’s also a conservation paradox, then, for something of such scientific and cultural significance exists mostly in labs and pet tanks around the world now. Luckily, they do well in captivity, but most of the axolotls today come from the same ones the French took from Mexico to Paris during an expedition in 1863 and are, therefore, inbred and not ideal for studies. 

Luis Zambrano González, a biologist and professor at UNAM, has been researching axolotls in this area since the 1990s. He explained that the axolotls placed in the wild come from UNAM’s specialized laboratory where healthy specimens are bred in controlled environments to make sure there is no relation to one another. Most of them come from an original census he conducted of the lake back in 1998.

The team and I get back in our canoes and stop over at the chinampa next door to accomplish one of the day’s most important tasks: collect cow manure. A lot of cow manure. “This is the best fertilizer you can ever use,” Sumano tells me as he’s loading four 50-pound open buckets of manure onto our canoe. “It’s too bad most farmers don’t use this natural fertilizer anymore,” he continues. “There is nothing like the nutrients and probiotics in here. You have everything you need.” 

Being that chinampas are an Indigenous form of farming, they are highly sustainable agricultural systems. A type of biofertilizer, manure gets broken down with water and is fermented in sealed vats until it’s ready to be used. Sumano breaks off leafy branches from a tree hovering over our canoe to protect and cover the manure from too much sun, and we set off to our next stop. 

Giovanni Santana’s chinampa is more overgrown than de La Cruz’s with no apparent path to anywhere. Sumano and I make our way through dense bushes, pushing away branches until we arrive at a small canal outlined in aquatic plants and covered by a vibrant green algae. Algae growth benefits aquatic life because the organisms produce oxygen as they photosynthesize. (In fact, ocean algae are responsible for 70% of the oxygen on Earth.) Behind the water is a large green field, and my eyes are squinting—not from the sun but, instead, from adjusting to the all-consuming amount of green before me. I’m contemplating if I walked out of the bushes and into a Monet. 

Sumano kneels on the earth and starts to gently push away the tiny green algae and submerge his hand in the water; it is crystal clear. Visibly satisfied, he shoves his hand deeper and pulls out plants from the bottom, revealing perfectly white, clean roots. Coming up to me excitedly, showing off the roots, he explains: “Now this is what the roots should look like. This water is perfect. It’s almost ready for the axolotls.” This canal was in the final stages of habitat restoration, and I never felt so happy to see roots in my life. 

After a brief snack break in the canoes, we stop by to visit another chinampa even deeper into Xochimilco. We check on giant vats fermenting with a previous batch of manure. Sumano approves of the quality, so we go check the water next. The canals are very new here. So far, they look like dirt ditches with brown water. The ditch leads out to the larger canal system where our boat is docked, and there’s a couple meters of branches and brush tangled densely in the water ahead of the opening. “The barrier is definitely strong enough against the tilapia,” the team mentions, looking at the entanglement. 

As writer Andrea Wulf summed up in The Invention of Nature on naturalist Alexander von Humboldt’s 19th century findings: “When nature is perceived as a web, its vulnerability becomes obvious. Everything hangs together. If one thread is pulled, the whole tapestry may unravel.” With his research, Humboldt was the first explorer who not only postulated human-induced climate change, a concept we now know as a simple fact, but also the cascading effects we could have on our environment. The story of tilapia and the axolotl, like countless other human interventions in nature, is an unfortunate example of pulling the wrong thread. 

Introduced by the Mexican government in the 1970s to combat hunger, tilapia and carp quickly decimated what was left of the already-dwindling wild axolotl population. For millennia, the axolotl had existed with virtually no predators until the invasive fish were dropped in. Unknown to those who made that decision, axolotl eggs and juveniles became their food source. From 1998 to 2020, the axolotl population went from 6,000 per square kilometer to 35. Efforts to remove the tilapia from Xochimilco by fishing them have been ineffective, so rebuilding the axolotl habitat means making it tilapia-proof. Hence, the barrier of branches and brush. 

After we move on, I see a man rowing an elderly lady who is sitting with an umbrella to shield her from the now beating sun. Large pelicans are wading next to us, herons are scooping up lunch, and little bubbles from fish aerate out from the sides of lily pads as we twist and turn, deeper and deeper through the labyrinthian canals. We pull over at the chinampa of Dionisio Sandoval. We’re here to collect aquatic bugs and fish from the new canals on this island. 

“For us, the Xochimilcas—who have deep roots regarding the axolotl—they are our ally, allowing us to also restore our agricultural activities while restoring the great Anahuác for future generations,” Sandoval says, referring to Anahuác, the Nahuatl word for modern-day Mexico City. 

Indigenous to Xochimilco, he is passionate about the restoration of the axolotl habitat. Two buckets are teeming full with life as I examine the contents. Countless species of tiny bugs and fish thrash around in the water. Sumano pulls one out. Wriggling in the palm of his hand with a familiar face but with a double tail I’ve never seen, he informs me that it’s a dragonfly. And that’s when I learned dragonflies are born in water, aquatic animals until they metamorphosize, being reborn as a creature that flies and breathes. 

Nearing the end of our day, we stop at the chinampa of Miguel del Valle, who stands as an example of a finished ecosystem where axolotls have successfully been rewilded. His chinampa doubles as a place where people can come learn about agriculture and practice gardening hands-on. Green, lush, and full of crops, his fields sit alongside the canal. It’s similar to Santana’s, abundant with algae and flora in every crevice along the water, including peace lilies dotting the edges. 

We complete the water check: hand in, water clear, hand deeper, white roots. A healthy population of axolotls have been happily rewilded here, thriving in the dark swampy water as they were meant to. “If we’re lucky, this is what we achieve,” Sumano says. “It’s perfect. We don’t have to interfere anymore.” A prime example of symbiosis, the work here is done. After all, when nature is operating in its natural state, it doesn’t need us. This year, the team has reintroduced 12 axolotls into their newly restored habitats, which are still under evaluation, with the goal of rewilding 40 by the end of 2022. 

There’s been a rumble in the distance, gradually getting louder as the sky turns a golden gray. We make a pit stop at Santana’s to drop off the bugs in his canal. Sumano is showing off all the yummy future axolotl food we gathered, pouring it into the water. As we row back, the sky finally opens. Not only do the birds grow louder in the build up to the rain—the croaking of frogs has returned. Soon, only the heavy downpour drowns out the surround sound the animals provided. 

“Señor de la Cruz must be happy,” Sumano and I shout over the rain.