In Mexico City’s precolonial canals, scientists aim to save ancient salamanders

The rickety rowboat has been traveling for about half an hour through Xochimilco, a precolonial borough in southern Mexico City, past canals, ditches and meadows when it docks at a small strip of land. Vegetables are grown on this chinampa, a strip of farmland originating back in the Aztec era, more than 500 years ago. In a shallow ditch, work is underway to protect an authentic inhabitant of this place: the Mexican axolotl (Ambystoma mexicanum), an endangered freshwater salamander found only in the 25-square-kilometer (9.6-square-mile) ecological park that is part of the neighborhood.

Those who navigate through the still waters here can hardly imagine that about 20 minutes away lies Mexico’s bustling capital. As far as the eye can see, farmland lies surrounded by human-made ditches. Herons stand frozen still along the shore; ducks swim through the water with their offspring. Several times, a farmer passes along, in a wooden sloop, his hat against the burning sun, pushing his boat forward with a long pole. It’s a lush, serene environment where scientists work to preserve a cultural symbol, endangered by habitat loss, invasive species and loss of water quality.

Vivian Crespo and Paula Cervantes, researchers at the National Autonomous University of Mexico (UNAM), get out of the boat and walk to the ditch, where just above the surface the top of a large, square cage made of bamboo and plastic netting lies. Inside swarm three male axolotls, part of the UNAM research project that seeks to help increase the dwindling axolotl population. Among other things, researchers are measuring water quality, improving it and working with chinamperos, the farmers who have been working these lands since long before Mexico’s founding.

The axolotl is closely associated with Mexico’s history and culture. The salamander, which owes its name to the Aztec fire god Xolotl, is a popular figure; you can spot it on the 50 peso ($2.78) bill, in Mexico City’s tourist brochures and in the works of Diego Rivera, and you can read about it in the works of Julio Cortázar and Aldous Huxley.

But cultural popularity is not the reason why UNAM, other Mexican universities and even foreign institutions are so interested in the salamander, says Vania Mendoza, a researcher for UNAM working on the project. “If an axolotl loses an arm or leg, it grows back within two months, and it functions as before. The same with its eyes or brain,” Mendoza says. “These regenerative properties are very interesting for the medical world, for researchers who want to know more about aging or who are fighting cancer.”

In the waters of Xochimilco, the researchers have 21 refuges, as the bamboo cages are called, placed in the canals separating chinampas. Each cage holds a maximum of three salamanders, each of the same sex to prevent reproduction. The researchers lift the cage out of the water in the ditch next to the chinampa, drain the water from the cage and set it on its side along the ditch. Crespo climbs in and searches among the water plants for the black, slippery critters.

Once the three animals are put into a container filled with ditch water, measuring can begin. First, she scans the male salamanders, which are all chipped. “Number 102489,” Crespo whispers. She carefully places 102489 next to a yellow tape measure. “Wow, this one has grown a lot, and just in one week!” The axolotl also appears to have gained considerable weight. In this ditch, where they live on water fleas, among other things, these axolotls clearly feel at home.

They feel less comfortable, however, in the rest of Xochimilco’s waters. Water quality has been significantly reduced by the increasing urbanization of the neighboring metropolis of Mexico City, and in the ‘90s, the municipality released exotic rainbow trout, African tilapias and Asian carp – predators of the axolotl – to promote fishing. The population of Mexican axolotls has declined dramatically, Cervantes explains: 36 per square kilometer, according to the last census from 2014; estimates point at some 6,000 axolotls per square kilometer hundreds of years ago. Habitat has also declined by about 99.5% in recent decades.

Once, axolotls thrived in the waters around Mexico City. When the Aztecs built Tenochtitlan, the predecessor of today’s capital city, they built an innovative system of canals and dikes around a huge lake. Chinampas were the epicenter of agricultural production, with palaces and temples towering over the farmlands. The axolotl did so well in these clean, shallow waters that the Aztecs even considered the salamander part of their diet.

When the Spaniards arrived, they drained the waters, building Mexico City on top of that. Only Lake Xochimilco remained — the last remaining home of the axolotl.

The axolotl can breathe in four ways, including through its skin, and poor water quality can make them sick. One of the first things Crespo and Cervantes do on arriving at a refuge is to check the water quality. Farmers on the chinampa play a big part in keeping the water clean. They will be compensated if they make an axolotl refuge in a ditch adjacent to their land: small compensation. Mendoza explains: “We help maintain the chinampas, and because they form part of the program, they guarantee their products are organic and free of agrochemicals. It helps them to sell their products, and our university helps them to sell at markets.”

Pedro Méndez has a cage hanging in the water, but the researchers doubt that this ditch is clean enough to house axolotls. Crespo and Cervantes brought a bucket of coontail (Ceratophyllum demersum) to assist him. Besides providing a perfect habitat for the axolotl, the green plant is also perfect for purifying water. Despite agreements with farmers, there is a new threat to the salamanders and researchers. “Because it’s so quiet here, people are starting to build houses on the farmland,” Crespo says. “To escape from the city, to live by the water — we are now starting to see more and more construction here. Although there are rules prohibiting this, contractors are flouting them. The municipality must intervene or it will get out of hand.”

In addition to the refuges, UNAM has a laboratory in which dozens of younger axolotls are kept before they go to the larger cages in the wild.

“This program is not cheap. And besides, contributions to science have drastically decreased under the current government,” Mendoza says. A UNAM campaign in 2023 raised international attention and more than $26,000, but funding remains insufficient. President Andrés Manuel López Obrador reduced the Ministry of the Environment’s budget by more than 30% in his six-year term.

Science has also suffered under his rule: Conahcyt, the national institute through which the most important research projects in Mexico are funded, is spending less on science, and other funds have been slashed. Money intended for research was used by the government to fund major infrastructure projects, such as the Tren Maya, a project that has caused irreparable damage to archaeological sites and nature on the Yucatán Peninsula.

Claudia Sheinbaum’s election does not necessarily bring scientists more hope. Although Sheinbaum herself studied at UNAM and was part of the Intergovernmental Panel on Climate Change, IPCC, she has promised to continue the bulk of her political mentor López Obrador’s projects, leaving scientists unconvinced that research funding will improve under her presidency.

For young scientists like Crespo and Cervantes, it makes no difference. They continue to get in their rowboat every week, heading to the chinampas to measure salamanders. Their next big effort is in September, when they will run a census of the axolotl population in Xochimilco, the first one in the last decade. But how do you measure how many salamanders are living in such a dense area?

“There are two ways to measure the number of axolotls in this area,” Mendoza says. “The first is by analyzing water: What do we find there in terms of cells, droppings of the axolotl, and what does that tell us about the numbers of salamanders? That way, we can see right away what the situation is with other fish in Xochimilco.” The second way is more traditional, by fishing marked areas with nets and seeing how many axolotls are taken from the water. Mendoza says she hopes the results will be better than in 2014. “We’ve been doing good work, and the chinamperos are really open to working with us. So, there should be progress.”

But Mendoza still worries about how urbanization may impact the species. “The water just isn’t clean enough. If we were to release all the axolotls from the laboratory here now, it would be a bloodbath. There is no way to survive here yet.”

Banner image: The top of an axolotl refuge, lying in the shallow water next to a chinampa. Image by Boris van der Spek for Mongabay.

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