We discovered the first beaver population in the Tagus River

The European beaver (Castor fiber) is the largest rodent in Europe and is a native species that disappeared from the Iberian Peninsula in historic times, probably due to human causes (Román & Aguilar-Gómez 2023).

In 2003, the species was reported again in Spanish territory, specifically in the Ebro river basin (Ceña et al., 2004), where 18 individuals were illegally reintroduced. Although it tried to avoid it, the species managed to successfully expand across the Ebro basin. In recent years, different authors have reported new locations with beavers. Calderón et al., 2022 have described the presence of beavers in the Tormes River (Cuenca del Duero) and Burón et al., 2024 have reported beavers in the Guadalquivir River Basin.

Recently, colleagues from the Ideas MedioAmbiental team have documented and described a new beaver population in the Tagus River, the first to be described in the Tajo basin (Ansón & García Prendes 2024).

The unbridgeable distances between these isolated populations in such a short time suggest an illegal episode of translocation of specimens, which is alarming given the case that protected fauna is being transported without justification or risk analysis.

Currently, according to scientific consensus, the species is native, is under a degree of protection and is included in Annexes II and IV of Directive 92/43/EEC, of May 21, 1992, relating to the conservation of natural habitats and wild fauna and flora.

References:

Anson, M. & Garcia Prendes, C. 2024. Galemys 36:23, xx DOI: 10.7325/Galemys.2024.O3

Burón D., Sancho J. R. & Samperio, J. C. 2023. The beaver appears in the Guadalquivir basin. Galemys, Spanish Journal of Mammalogy3.5 (1): 11

Calderón, T., Balmori-de la Puente, A., Caballero, J. M., Rodríguez, D., Caballero, A., & Balmori, A. 2022. The Eurasian beaver in the western Iberian Peninsula. Hystrix, 33, 212-214.

Ceña J.C., Alfaro I., Ceña A., Itoiz U., Berasategi G. & Bidegain I. 2004. European beaver in Navarra and La Rioja. Galemys, 16, 2, 91-98

Román J. & Aguilar-Gómez C.M. 2023.Until when did beavers historically inhabit the Iberian Peninsula? The importance of consulting primary sources to avoid errors in historical ecology. Historical Biology, 1-5.

Cover photo taken by Celia García