Pyrenees Small Mammal Almost Invisible, Water Reveals It

It sports a mobile snout, webbed feet, and lives in the fast-flowing torrents of the Pyrenees. Yet catching sight of a desman is almost a feat in itself. To determine whether it still frequents certain rivers, scientists are now pursuing an astonishing lead: looking for DNA fragments left behind in the water.

In Pyrenean torrents, an odd little mammal almost always escapes view

At first glance, the desman des Pyrénées seems straight out of a mythical bestiary. This small semi-aquatic mammal possesses a movable snout reminiscent of a tiny trumpet. It also sports a long tail and feet adapted for swimming. Yet, Galemys pyrenaicus does exist, notably in the Pyrenean river networks and the northwest of the Iberian Peninsula.

Seeing it is another matter. The animal readily lurks along banks, under rocks, and in rough, rapid waters. It is safe to say that observing it is particularly challenging. Even specialists sometimes have to deploy substantial resources. In 2023, naturalists carried out an operation in the Orlu reserve, in Ariège. Despite this mobilization, they captured only a single individual.

This discretion hides above all a troubling situation. According to the French Biodiversity Office, the desman’s range in the French Pyrenees has fallen by more than 50% in thirty years. Several threats explain this retreat. The artificialisation of riverbanks, dams, changes in flow, and pollution are progressively fragmenting a habitat on which this mammal relies very closely.

When the animal remains elusive, a few molecules left in the water take over

How do you search for a species that almost no one sees? Naturalists traditionally scan the banks for feces. Studies also indicate they may use captures or radio-tracking. But a more surprising lead is advancing: environmental DNA, or eDNA. This method seeks the genetic material that organisms leave behind in their environment.

In a river, cells, secretions, or organic matter can release tiny DNA fragments. Scientists then sample water and analyze it in the laboratory. This technique can potentially reveal a presence without needing to capture the animal. For the desman, the OFB (Office Français de la Biodiversité) has notably carried out sampling in Ariège. These analyses aim to assess the effectiveness of this approach for semi-aquatic mammals.

Behind this genetic inquiry lies a long battle to save the “trumpet rat”

This research does not spring from nowhere. Between 2014 and 2020, the European LIFE+ Desman program pursued an ambitious mission: to better understand the species, but also to protect its habitats. Its initial budget reached precisely €2,672,707. Several Natura 2000 sites in the Pyrenean massif thus hosted the various actions of the program.

The LIFE program is finished, but monitoring continues. A second National Action Plan has taken over. The DREAL Occitanie coordinates it, and the Conservatoire d’espaces naturels d’Occitanie ensures its implementation. Its objectives are multiple: improve knowledge and protect sensitive areas. It must also develop methods suited to monitoring this particularly hard-to-detect animal.

L’environmental DNA is therefore not a magic wand. The national plan itself stresses the need to test and improve the method for the desman. A positive detection can provide valuable information to specialists. However, researchers must interpret the absence of DNA with caution. It is not, on its own, sufficient to prove that the species has abandoned a river.

The desman could ultimately teach us far more than its mere presence in a river

Protecting this animal also means rethinking the way we view the Pyrenean torrents. The desman depends on well-preserved aquatic habitats that are rich in invertebrates. It must also find food and shelter there. Its rarity draws attention to broader changes—changes that affect an entire ecosystem, from flow variations to the fragmentation of habitats.

The paradox is striking. The desman becomes increasingly difficult to observe. Yet scientific tools can search for ever-smaller traces of its presence. Tomorrow, a few molecules carried by a torrent could help better target conservation efforts. One question remains: how long will these traces continue to attest to living animals?