In Mexico City, Scientists Hunt for an Endangered Creature

Sixty years ago, residents of a canal-crossed borough in Mexico City could pluck axolotls—the large salamander reminiscent of a tiny dragon—out of the water with their hands because they were so plentiful. Now it's almost impossible to find them in the wild. That's why scientists from Mexico's National Autonomous University are filtering murky waters in the Xochimilco neighborhood for traces of the endangered creature's DNA, per the AP.

"We all shed DNA along our path across the world and that can be captured by filtering air or water," said biologist Luis Zambrano, from the university's ecological restoration lab. As they try to monitor the axolotls' dwindling numbers, scientists increasingly rely on this technique as their nets come back empty during periodic surveys of the population, which is only found in Xochimilco. They sample water taken from the canals and filter it for environmental DNA, or the genetic particles left by animals and plants that have contact with the water. That's then compared to the profiles contained in a genetic library put together some years ago by British scientists, said Esther Quintero of Conservation International in Mexico, which has collaborated with Zambrano since 2023.

Scientists collected water from 53 locations in Xochimilco: 10 inside refuges where water is filtered and the water is cleaner, and 43 outside those areas. They found axolotl DNA inside the protected areas and in one site outside them. Referring to the one unprotected area, Zambrano said "it's very little," but a sign that there is the possibility of resilience, even with continuing environmental degradation and pollution of the canals.

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So far, the researchers have only searched a third of Xochimilco with the environmental DNA technique and the manual work with nets, but they plan to continue the work and hopefully present an updated census early next year. The trend, however, is not good. From an estimated 6,000 axolotls per square kilometer in 1998, there were only 36 per square kilometer in the last census, in 2014.