Eurasian beaver reintroduction

The Eurasian beaver was hunted and trapped to the point of near extinction. Fossil evidence shows that the Eurasian beaver lived from Western Europe to the Chinese-Mongolian border. By the beginning of the 20th century, only about 1,200 Eurasian beavers were left in this area,[1] surviving in eight relict populations in Europe and Asia.[2]

Beavers are considered ecosystem engineers for their ability to create complex wetland ecosystems by tree-felling, dam-building, and burrowing.[3] Wetlands provide habitats for many other species of fish, birds, mammals, and vegetation, leading to increased biodiversity.[4] Beaver dams push water laterally onto flood plains, increasing groundwater and surface water storage.[3] Presence of beavers can improve water quality through sediment trapping in dams, and provide natural flood control.[5] Ponds and canals store water in areas susceptible to drought.[6] Beaver reintroduction causes flooding in areas that were not previously flooded. Over saturation causes some plants and trees die, increasing coarse woody debris (CWD) in the area. CWD attracts wood insects, and provides nesting holes for waterfowl[7] and areas of refuge for fish.[8] Trees and vegetation migrate to drier areas, leading to diversified plant species.[7] Presence of beavers increases numbers in aquatic invertebrates, insects, amphibians, birds and bats.[9] Ponds create nursing ground for fish, increased fish habitat and habitat complexity. Beaver dams can have a negative impact on migratory fish such as salmonids, preventing fish from moving upstream to headwaters.[8] Deep beaver ponds provide overwintering habitat for fish, reduce ice cover, and stabilize temperature regimes.[5]

Beavers are reintroduced through planned and unplanned releases, such as escapes from captive populations. Unplanned releases can happen through escapes from zoos or wildlife centers, or through natural spread.[10] Planned releases are managed by governmental organizations and environmental non-profits. These are most successful when managed locally. Successful trials to reintroduce beavers start by raising community awareness and support, through community outreach and education.[11]

The reintroduction of a species can cause rapid change to high-use domesticated landscapes. These changes cause a range of emotional reactions to the community present. Attempting to understand these reactions is important for managing organizations to aid in coexistence between humans and beavers, and population success.[12] The health of a reintroduced species impacts humans and domesticated animals, and other wildlife. Health assessments should take place before and regularly after its reintroduction. In unplanned releases or escapes, it is difficult to produce a health baseline of a species.[10]

As a flagship species, beavers raise awareness and resources for wide-scale riparian and woodland restoration programs by stimulating conservation awareness. Beavers increase ecotourism, as interest in beavers and other biodiversity in ecosystems with beavers increases. Beaver ecotourism has positive socio-economic impacts for local businesses and community members.[13]

By 2003, due to reintroduction and protection programs, there were about 639,000 beavers in Europe.[14] Successful Eurasian beaver introductions throughout Europe, including England, Scotland, Bavaria, Austria, Netherlands, Serbia, Denmark, and Bulgaria.[9] These successes resulted in Eurasian beavers listed as being of least concern on the (IUCN) red list due to its fast recovery in Europe.[9] Initial reintroduction populations show a time lag between the rate of population growth and the resource growth rates. This is seen in an initial population growth followed by decrease in populations to settle into the amount of resources available to the beaver populations.[15]

• 1922–1939 – Sweden: About 80 beavers were reintroduced to 19 different sites over a 20-year span with an estimated 130,000 individuals present in 2014 [16][17]
• 1923 - USSR: Voronezh Nature Reserve established with the intent of protecting and restoring Beaver populations.[18] From 1934 to 1977, approximately 3,000 Eurasian Beavers from Voronezh were reintroduced to 52 regions of the USSR, from Poland to Mongolia.[19]
• 1935 - Finland: 17 Eurasian beavers were reintroduced, then two years later release introduced North American beavers sourced from New York. At the time, a difference between the species was unknown. Today, the North American beaver is considered an invasive species in Finland, and outnumbers Eurasian beavers 5:1. The species has since entered Russia.[20]
• 1966–1982 – Bavaria: From extinction, reintroduction has increased to pupation to an estimated 6,000 individuals. As one of the oldest reintroduction sites, it is often visited and studied for the management practices.[21][22][23]
• 1976–1982 – Austria: Around 40 individuals were introduced in the Danube-Auen National Park downstream of Vienna. They have since then spread to the waters around the Danube inside the city as well. Today (2020), an estimated 230 beavers live in the Vienna region outside the national park proper.[24]
• 1988 – Romania: 21 beavers were successfully reintroduced in 1998 along the Olt River, spreading to other rivers in Covasna county [25][26]
• 1996-1998 - Croatia: Beavers were extinct in the Balkans for fifty years before their reintroduction. Beavers were sourced from Bavaria.[20]
• 1999 – Denmark and Northern Zealand: 18 beavers were released at Klosterheden in West Jutland. Since then, other beavers have been released at Arresø in North Zealand.[27][28]
• 2003 – Spain: 2003, beavers were reintroduced to the Ebro in Spain, with plans for further reintroductions to The Guadalquivir, Guadiana, and Tajo (Tagus) river systems [29]
• 2004 - Serbia: Beavers were extinct in the Balkans for fifty years before their reintroduction. Beavers were sourced from Bavaria.[20]
• 2005 - Bosnia: Beavers were extinct in the Balkans for fifty years before their reintroduction. Beavers were sourced from Bavaria.[20]
• 2009–2014 – Scotland: 11 beavers were released in 2009 and four beavers were released in 2014 in the Knapdale forest [30] and 56 beavers were found at the River Tay, becoming its own study [31][32]
• 2019 – East Anglia: A pair of beavers was reintroduced to North Essex as part of a pioneering natural flood management scheme for East Anglia [33][34]

A "say no to beavers" sign in the Isle of Wight.

Beavers can negatively impact agricultural areas, by flooding farm lands and decreasing crop yields. Beaver scientists manage these issues by relocating beaver dams, using water sounds to trick beavers into building the dam at different places, or using pipes in dams to help control water levels.[6] These finding were also suggested for instances when beavers created dams blocking man-made structures such as culverts. In one case, poles were placed 10 feet in front of a culvert, changing the place of the water flow sound, in which the beavers build the dam at the poles, allowing for runoff to go through the culvert.[6] Farmers have reported beavers burrowing in their fields, leading to damage to machinery such as tractor and damage to crops.[35] Governments have addressed this issue by voluntarily compensating the farmers for these damages. Translocation and lethal control are options that should be used as a last resort, as both can negatively impact whole ecosystem.[36]