Biologist says most recent attempt to net creature in the Xochimilco network of lakes resulted in none being found

This article is more than 6 years old

This article is more than 6 years old

Mexico's salamander-like axolotl may have disappeared from its only known natural habitat in Mexico City's few remaining lakes.

It is disturbing news for the amphibian which has a slimy tail, plume-like gills and mouth that curls into an apparent smile.

Growing up to a foot long (30 cm) and known as the "water monster" or the "Mexican walking fish", its only natural habitat is the Xochimilco network of lakes and canals, which are suffering from pollution and urban sprawl.

Biologist Armando Tovar Garza, of Mexico's National Autonomous University, described an attempt last year by researchers to try to net axolotls in the shallow, muddy waters of Xochimilco as "four months of sampling zero axolotls".

Some axolotls still survive in aquariums, water tanks and research labs, but experts said those conditions were not ideal because of interbreeding and other risks.

Axolotls use four stubby legs to drag themselves along the bottom or thick tails to swim in Xochimilco's murky channels while feeding on aquatic insects, small fish and crustaceans. But the surrounding garden islands have increasingly been converted to illicit shantytowns, with untreated sewage often running off into the water.

The Mexican Academy of Sciences said a 1998 survey had found an average of 6,000 axolotls for each square km, a figure that dropped to 1,000 in a 2003 study, and 100 in a 2008 survey.

Tovar Garza said it was too early to declare the axolotl extinct in its natural habitat. He said that in early February, researchers will begin a three-month search in hope of finding what may be the last free-roaming axolotl.

The searches "on almost all the canals have to be repeated, because now we are in the cold season, with lower temperatures, and that is when we ought to have more success with the axolotls, because it is when they breed," Tovar Garza said.

Researchers, who have been alarmed by the creature's falling numbers in recent years, have built axolotl "shelters" in Xochimilco.

Sacks of rocks and reedy plants act as filters around a selected area and cleaner water is pumped in to create better conditions. The shelters were also intended to help protect the axolotls from non-native carp and tilapia, which were introduced to the lake system years ago and compete with axolotls for food.