Batbold, J., Batsaikhan, N., Shar, S., Amori, G., Hutterer, R., Kryštufek, B., Yigit, N., Mitsain, G. & Palomo, L.J.
Amori, G. (Small Nonvolant Mammal Red List Authority) & Temple, H. (Global Mammal Assessment Team)
The Eurasian beaver has shown good recovery across much of its range, as a result of conservation programmes. The highest numbers are found within Europe. Conservation measures are ongoing to prevent the population declining again and as long as these continue, there is no reason to continue to assess the species as threatened or Near Threatened. Now Least Concern. However, the Asian populations remain very small and under serious threat, and these populations urgently need conservation measures.
Entre las diferentes poblaciones, la tasa de crecimiento varia, pero por lo general la mayoría de los ejemplares no alcanzan su madurez sexual en el primer año, sino hasta el segundo invierno, mas o menos al año y medio de edad. Aunque también se ha demostrado que la madurez sexual de los ejemplares dependen mucho de la constitución de la colonia.
Eurasian beavers, Castor fiber, once heavily populated all of Europe and Asia. However due to overhunting for fur and castoreum, a chemical from their castor sacs, and habitat loss, populations fell nearly to extinction. By the 19th century most countries in Europe and Asia had no remaining beavers. By the 20th century an estimated 1300 beavers remained in the wild. Management efforts and reintroductions have resulted in Eurasian beaver population increases. Populations are now established in France, Germany, Poland, southern Scandinavia, and central Russia. However, populations are small and scattered throughout this area.
By the beginning of the 20th century, the global population had been reduced to eight populations, totalling approximately 1,200 individuals (Halley and Rosell 2002). Protection (beginning with a hunting ban implemented in Norway in 1845), natural spread and reintroductions have resulted in a rapid recovery in numbers and range, particularly in Europe. In 1998, the global population was estimated at 430,000 (Nolet and Rosell 1998), by 2002 it had reached at least 593,000 (Halley and Rosell 2002), and in 2006 the minimum estimate was 639,000 (D. Halley pers. comm. 2006). This is almost certainly a considerable underestimate, as both population and range are in rapid expansion (Halley and Rosell 2002, 2003; D. Halley pers. comm. 2006). Considerable further expansion in range and population, especially in western Europe and the lower Danube basin, can be expected. If current trends continue, the Eurasian beaver will be a fairly common mammal in much of Europe within the next few decades.
However, populations in Asia are still considered small. In Mongolia, reintroductions have been successful and the population has reached 150, and in China the population is about 700 (Halley and Rosell 2002, EMA Workshop 2006, Smith and Xie in press).
In Mongolia in 1964, the population size was estimated to consist of 100-150 individuals (Stubbe and Chotolchu, 1968), rising to 200 individuals by 1973 (Zevegmid and Dawaa, 1973). In 1991, surveys estimated there to be approximately 300 individuals along Bulgan and Hovd rivers (Stubbe et al., 1991). The most recent population assessment was conducted in 2004, which recorded 40 lodges along Hovd River and estimated the population to consist of 130-150 individuals (Shar, 2005). Ten beaver settlements were recorded in the Tuvan section of Tes River in 2005 (A. Saveljev pers. comm.), and the Mongolian section of this river is believed to contain a similar beaver population (M. Stubbe pers. comm.).
The Chinese subspecies of the Eurasian Beaver (C. f. birulai) is one of the rarest and least known aquatic mammals in China. In the 1970s it was believed that only 100 animals remained in fewer than 20 family groups. Currently, only one substantial population is known, at the Buergan River Beaver Reserve along the Xinjiang-Mongolian border - a narrow strip 50 km long and only 500 m wide. Here the population is estimated to be only 500 animals, and only 700 may live in all of China.
Es necesario legislar el aprovechamiento de la especie, se disminuir la tala de los bosques en los sitios en que habitan y permitir que las corrientes de agua puedan seguir libres no creando grandes represas.
The beaver's historic decline was caused by over-hunting for fur, meat and castoreum (a secretion from the scent glands), combined with loss of wetland habitats. Beaver populations were severely reduced in most countries by mediæval times, but the species clung on in marshes and other inaccessible places until the advent of efficient steel traps and accurate firearms in the 17th century; and then through to the 19th century there was a rash of final extinctions for these reasons combined with drainage of many of the large marshland areas in which the species clung on (all of the European refugia where the species survived, except in Norway, are extensive marshlands).
Today, beaver populations in Europe are expanding rapidly, and there are no major threats (e.g. threats of a magnitude likely to cause decline at the regional level). Competitive exclusion of the native European beaver C. fiber by its American cousin C. canadensis may be a threat in parts of Finland and north-west Russia, but it is not a major threat regionally. In Europe North American beavers are now confined entirely to Finland and north-west Russia, where populations are increasing only slowly (due to heavy harvesting). The former population at a reservoir near Paris has been removed, and populations introduced to Poland and Austria have apparently gone extinct in competition with C. fiber, the opposite of what has tended to happen in Finland and north-west Russia (it has been suggested that, due to differences in the life history of the two species, Eurasian beavers may have a competitive advantage at more southerly latitudes, whilst North American beavers may be more successful further north: D. Halley pers. comm. 2006). There are no serious prospects of further introductions (Halley and Rosell 2002, D. Halley pers. comm. 2006). The two species do not interbreed (Tattersall 1999). Road kill is an important source of mortality for some populations (Tattersall 1999). Rapidly expanding beaver populations may come into conflict with humans in some areas, as they do some damage to forestry and crops. Such damages should be put into perspective: they tend to be less severe than those caused by other species such as deer and voles, but are noticed because beavers are a new and unfamiliar species in areas where they have been recently introduced (Halley and Rosell 2002).
In Mongolia, illegal hunting for skins, meat and castoreum still occurs in some areas such as the Tes River. Habitat loss through selective clear-cutting of willow, upon which this species relies for food and shelter is also a threat; this is known to be occurring along the Bulgan River and is leading to isolation of small populations and inbreeding. Pollution of water systems is also a threat. A hydroelectric dam in the Chinese section of the Bulgan River prevents migrations in this area (M. Stubbe pers. comm.).
In China, firewood gathering has depleted much of the forest on which the beavers need to subsist; additionally heavy grazing pressure has further reduced vegetation needed by beavers.