Student Article – Beavers on the march

Beavers on the marchLucy Mooney

Reviewed by Dr Chiara Pazzagli

Pembrokeshire College, Haverfordwest, Pembrokeshire, SA61 1SZ, UK

Lucy is a mature student studying ‘Access to Higher Education in Biosciences at Pembrokeshire College. She has taken part in workshops, which were part of the “Discovering Living Light” project (See Issue 1) at the Darwin Centre. She is very enthusiastic about all aspects of biology, and will study zoology at Exeter University.

Key words: beaver, Castor, flooding,


In 2016, the Scottish Government granted permission for beavers released during the Scottish Beaver Trial to remain living wild in the Knapdale area of Scotland (, 2016). This marks the first ever-successful reintroduction of a previously extinct mammal to the British Isles.  Further trials are underway in Devon and Cornwall and consultations are underway to reintroduce beavers to Wales (Elliot et al. 2017, Hailey et al. 2009). What is a beaver, what are the reasons for its reintroduction, and how will they affect the British countryside?

The beaver

Fig. 15 The Beaver

The beaver is a large semi-aquatic rodent, which builds dams, but was hunted to extinction in the UK in the 16th century. There are two species the North American beaver (Castor canadensis) and UK native species, the Eurasian beaver (C. fibre). The case for reintroducing the beaver rests on three main arguments, beavers aid flood management, improve water quality in rivers and increase biodiversity.

The problem

Flooding is becoming more common in the UK, causing many problems across the country. In 2014, extreme flooding of the Somerset Levels caused people to be evacuated from their homes, and £6 million was spent on dredging 8km of river. £100 million was designated for ‘The Somerset Levels and Moors Flood Action Plan’, and an estimated £200 million was lost from tourism in Somerset (Mann, 2016).   Beaver reintroductions are being considered to mitigate flood damage.

How beavers help prevent flooding

 A 2016 study of beavers in the Tamar in Devon, (Exeter University) found that their dams reduced water flow by an average of 22%.

 Also beaver dams filtered the river, improving water quality.  Samples taken below the dams had reduced quantities of:

Suspended sediment < 65%

Organic nitrogen < 35%

Phosphates < 80%

 Beaver dams trap suspended sediment. The reduced water flow means   substances heavier than water sink to the bottom.

Fresh water systems cover less than 1% of the Earth yet support 12% of all animal species.   Intense agricultural practices have caused a serious decline in species ( 2016). Therefore, it is important that we try to preserve and restore these vital ecosystems.

 Studies have shown the beavers ability to transform degraded agricultural land into   vibrant ecosystems, e.g. Scottish beavers increased biodiversity by 148% in 10-12 years (Law 2017). They increased areas of standing water,  increasing freshwater invertebrates. They raised light availability by felling trees allowing more plant species to flourish. 

The advantages and disadvantages

 Many anglers object to beavers, because dams impair salmon migration. However, beavers only build dams on streams that are about a metre wide. This means that on main river trunks, salmon migration is not affected.  The level of migration impairment is dependent on variables such as water levels, dam height and season (Verbickas 2015).  Nevertheless, effects of beaver dams on salmon populations will need to be monitored and no doubt, the Angling Trust will ensure this happens.

 Beaver tourism may boost rural economies; reintroduction of sea eagles to the Isle of Mull is estimated to have increased the islands economy by £5 million a year.  However, although this is a much-needed source of revenue for rural communities, those who benefit most from this are not the same people who are negatively affected by beaver presence. Although the damage caused is relatively small compared with the benefits brought by beaver, it is largely farmers who gain little to no economic benefit from beavers and who are detrimentally affected by their presence.

What the public think

A majority of the British public feel positively about the reintroduction of the beaver (Jones 2016).  The success of the Scottish Beaver Trial means plans to reintroduce the beaver to other parts of the UK are less controversial. After 400 years, the beaver is now resident in several areas of the UK.

Although beaver reintroductions are not without issue, it is tempting to agree with Paul Ramsey whose land is home to a family of beavers:

“When you consider that in Europe as a whole, this creature was on the very brink of extinction, and yet has made an incredible comeback, this is a fantastic conservation success story – and something we should be boasting about” ( 2012).


  1. (2012) ‘Beaver tourism’: can it work? [online] Available at: [Accessed 28 February 2018 09:14]. 
  2. (2016) UK Lowland Wetland Habitats [online] Available at: [Accessed 23 April 2018 18:18].
  3. Elliot, M., Blythe, C., Brazier, R.E., Burgess, P., King, S., Puttock, A., Turner, C. (2017) Beavers- Nature’s Water Engineers. 1st ed. [pdf] Devon: Devon Wildlife Trust, Available at:  [Accessed 18 February 2018 12:19]. 
  4. Hailey, D.J., Jones, A.C.L., Chesworth, S., Hall, C., Gow, D., Parry, R.J., Walsh, J., (2009) The reintroduction of the Eurasian beaver Castor fibre to Wales: an ecological feasibility study. 1st ed. [pdf] Trondheim: Norwegian Institute for Nature Research, Available at: [Accessed 10 January 2018 18:16]. 
  5. Jones, S. Campbell-Palmer, R. (2014) Scottish Beaver Trial: Final Report. [PDF] Available at:  [Accessed 09 December 2018]. 
  6. Law, A. Gaywood, M. Jones, K. Ramsey, P. Willby, N. (2017) Using ecosystem engineers as tools in habitat restoration and rewilding: beaver and wetlands. [PDF] Available at: [Accessed 10 January 2018 18:17]. 
  7. Mann, C (2016) Flooding in the Somerset Levels: 2014 [PDF] Available at:  [Accessed 20 January 2018 13:42]. 
  8. Puttock, A., Graham, H., Cunliffe, A., Elliot, M., Brazier, R., (2016) Eurasian beaver activity increases water storage, attenuates flow and mitigates diffuse pollution from intensively-managed grasslands [PDF] Available at: [Accessed 21 January 2018 16:27]. 
  9. (2016) Beavers are back in Scotland. [online] Available at: [Accessed 10 January 2018 14:22]. 
  10. (2016) Beaver Facts. [online] Available at: [Accessed 10 January 2018 14:32]
  11. (2016) Understanding the socio-economic impacts of beavers in Scotland [PDF] Available at: [Accessed 28 February 2018 10:44].  
  12. Verbickas, T., Stakenas, S., Steponenas, A. (2015) Impact of Beaver Dams on Abundance and Distribution of Anadromous Salmonids in Two Lowland Streams in Lithuania. PLoS ONE [online] Vol. 10 (4). Available at: [Accessed 25 February 2018 18:56]. 
  13. (2011) Sea eagles bring millions to Mull’s economy. [online] Available at: [Accessed 23 April 2018 18:28].

Beavers on the March

Student Article Review by Dr Chiara Pazzagli, Clinical Scientist and Patient Advocate at Novartis Institutes for BioMedical Research, Basel, Switzerland

What are the strong points of the article?

The subject matter of this article is likely to be of interest to a range of readers – those interested in conservation, natural and environmental science, but also budding scientists looking at water pollution and natural filtration systems. The writing style is accessible and the student shows a passion for her subject.

What could the student have done differently?

I would have liked to have seen a little more background of WHY beavers build dams and also some analysis of how reduced water flow causes sediments to sink. There was no explanation of why the reintroduction of sea eagles on Mull had boosted the local economy.

Building on what they have discovered, what further exploration would be useful/interesting?

As well as fleshing out the points above, I would love to know more about why beavers had been hunted in the past and more about their wider contribution to the ecology of their habitat. Conservationists would be especially interested in how species re-introductions are managed and monitored. The great thing about a good article is that, in addition to learning something, you always have lots of questions at the end!

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