Beavers and Poole Harbour

Introduction The Poole Harbour Catchment Partnership works together to improve the waterbodies of Poole Harbour; its groundwaters, rivers and the harbour and coastal waters. This includes activity aimed at reducing the excess nutrient and sediment, restoring more natural flows and fish populations. To achieve these benefits, a significant change will be needed in how land and river systems are managed at a landscape scale. Partners are reviewing the potential that beavers may offer to contribute to these aims to rebuild the natural functions of our rivers. Beavers are a ‘keystone’ species, modifying rivers and wetlands and allowing other native wildlife to thrive. However, we have built on and modified these flood plains since beavers died out in the UK over 400 years ago.

The potential return of beavers in England arouses strong and varying views across the partner organisations. The role of the Beaver working group is to share these concerns, to review both the benefits that may be achieved and the issues and costs that would be incurred. The catchment partnership has no regulatory role in the release of beavers but in communicating the experience from Europe and Devon, can facilitate agreement and funding for their management, should permission for their release be granted in the Poole Harbour catchment.

What you may not know about Eurasian Beavers Eurasian beavers are one of the largest rodents, about 1.3m from nose to tail and weighing about 18kg, although they are smaller than their North American cousins.

Beavers are vegetarians- they eat riverside plants and grasses as well as tree bark and shoots. They don’t eat fish.

Beavers like to stay in deep water (>70cm deep) so they stay close to rivers. In shallow water they will build dams of mud and branches to create pools and they can dig channels to places they want to visit. Dams can be shallow or tall and are generally built only in narrower tributaries (<6m wide) but unlike manmade weirs, they are ‘leaky’, allowing water and fish to pass through or over, especially in high flows.

Beavers fell trees to collect these branches and to eat the bark but most British trees coppice well and regrow quickly. Felling riverside trees opens up the tree canopy which, along with the wetlands formed, creates diverse habitats for water voles, amphibians, dragonflies, birds and plants.

Beavers live in family groups of a pair with their last two litters. They are adult at 3 years and live for 7-8 years in the wild, having 2-3 kits per year. At 2 years the youngsters move out and establish a new territory. The families live in burrows or lodges.

Where are beavers found? Eurasian beavers were once widespread across Europe and Asia, and were common in Britain. From an original population of around 100 million, in fragmented populations in Europe, they were hunted for their fur, flesh and their valuable oils until they died out in the 16th Century in Britain and about 1,200 beavers remained by the late 19th century in Europe.

Since the 1920s, around 200 formal reintroduction projects have taken place across 25 European countries allowing beavers to spread naturally and slowly repopulate mainland Europe. Beavers were reintroduced in Scotland from 2006, gaining native status in 2019.

Beavers re-established themselves in the River Otter in Devon in 2015 and can be viewed there. Other reintroductions have occurred in fenced sites in Devon, Cornwall, Gloucester and recently in Somerset, to trial their effectiveness in providing cost-effective solutions to reverse water quality problems, reduce flooding and improve biodiversity. www.pooleharbourcatchment.co.uk | [email protected]

What can beavers do for Poole Harbour? In 2017 Wessex Water asked the University of Exeter to review the evidence from other re-introductions to see whether it was feasible to use beavers to resolve or reduce the problems identified by the Poole Harbour Catchment Partners. These include excess nutrients (Nitrogen and Phosphorus), excess fine sediment and un-natural flow regimes. These issues, which are typical across many English catchments, are associated with rivers whose channels are disconnected from their floodplains and result in poor habitat for fish, insects, aquatic birds and mammals. Nutrient enrichment results in the extensive algal mats forming in Poole Harbour, harming the wildlife habitats for this site of European importance for birds and, additionally, and increases the treatment costs for drinking water supplies.

Mapping of beaver habitat suitability for the Poole Harbour catchment (Beaver Habitat Index) shows that beavers could establish well in these rivers and modelling of likely dam development (beaver dam capacity model) shows that the headwaters, a key area for mitigating flood risks, would attract dam construction. The lower reaches of main rivers like the Frome and Piddle are too large to be dammed.

North Devon trials showed that enclosed beavers both slowed and reduced the peak river flows in storm events and settled out the sediment in the ponded waters. Compared to the incoming water, the stream that left the enclosure had lower concentrations of sediment, Nitrogen and Phosphorus. The dissolved organic carbon (DOC) concentration increased, with water coming from lowland agricultural environments, which has unnaturally low DOC. DOC is the base of the aquatic food chain, so restoring DOC to more natural background levels should be a key ecological objective for wetland management.

Within 5 years, the new wetland in the North Devon trial stored 1000 cubic metres of water in 13 ponds (totalling over 1500m2 in area) and provided a habitat for frogs and small fish. Plant species and aquatic invertebrates also increased in number and distribution.

Do beavers affect fish?

Although beavers don’t eat fish, there is potential for impact in other ways. Beavers do increase the area of water habitat, with the connected marshes and pools being prime habitat for the invertebrate life that supports juvenile fish growth, whilst opening up shaded river banks. The ponding both reduces the peak flows in storm events, protecting small fry, and improves flows in channels during the summer. The increased insect populations provide food for fish such as trout and salmon, which are key species in the Dorset chalk streams.

The low number of British beaver trials in salmonid rivers means that we do not have detailed studies to answer key angler concerns that there is the potential for the sediment accumulation to smother gravels in ponds, and the impact of dams as barriers to migration of these species. However, experience on the Otter tributaries and in Scotland has shown that salmonids can pass the leaky dams except during low flows. The naturalisation of the river channels that

damming can bring has been shown to clean gravels in the River © Terry © Bagley

Otter, supporting successful spawning.

How fast are beavers likely to spread? Whilst no beavers have escaped from the existing, enclosed trials, their spread has been monitored from open sites elsewhere. On the River Otter, two were re-released plus two further beavers being introduced to provide genetic diversity. By 2019 there were 7 breeding pairs plus a further 6 apparent territories from single animals. Based on knowledge of their habitat preference and range, and their low tolerance of seawater, Exeter University have calculated that the rate of spread of beavers between rivers would be relatively slow; this would also apply to rivers in the Poole Harbour catchment.

www.pooleharbourcatchment.co.uk | [email protected]

As effective landscape engineers, water management by beavers can clash with our farming, residential and infrastructure interests within the natural flood plain. Experience elsewhere has shown that key issues include:

• Crop damage where it is a suitable beaver food, grown close to rivers.

• Felling valuable trees in orchards, gardens or specimen trees. • Localised flooding; where small streams are dammed the raised water levels may restrict access or damage infrastructure, property and crops. • Burrowing in banks, which may collapse when vehicles or

Remembering that beavers rarely travel more than 10m from rivers, these impacts are limited to areas where crops, access or infrastructure is within 20m of the river bank. Protecting a riparian zone of 20m for them would resolve 95% of the issues. It would also improve the interception of runoff and sediment from cultivated land.

Simple beaver management techniques include: • Simple tree protection using paints or wire netting • excluding larger areas with electric or permanent fencing; fitting tree guards or painting individual trees. • Reducing or limiting dams and dam height through electric fencing, physical removal (of either higher sections or whole dam) and ‘beaver deceiver’ devices to prevent localised flooding or blockages of channel infrastructure. • Removal of felled trees from footpaths • Trapping in, and relocation from, unsuitable zones.

How would we manage beavers, and what would it cost? In 2019, the leading reason for the poor state of English rivers is their historic modification and prevailing management. Beavers are natural river engineers and work for free, re-naturalising rivers, but the experience in Bavaria has shown that active management is needed in areas where people and infrastructure are close to the river. This includes lowering dams to control water levels, removing beavers from unsuitable habitats (by trapping) and advising landowners on protection for valuable trees. In Bavaria, two officers train volunteer wardens and operate a management scheme costing €2-3million (equivalent to £75-105,000 for the area of Dorset) per year, including compensation payments, damage repairs and protection of assets.

In the Poole Harbour Catchment Initiative, we understand that resolving the poor water quality and flooding issues for society will be at a cost, often to those who manage the riparian land rather than those who reap the benefits of clean and plentiful water and thriving wildlife. We support schemes which reduce pollution at source, or work with nature and these may be funded by those who benefit. Such schemes currently include the levies on development for Nitrogen and for mitigating biodiversity impacts (through BCP and Dorset Councils), plus water company Catchment Management schemes for nitrate reduction around drinking water sources, Poole Harbour SSSIs or that offset nutrients from Water Recycling Centres (Sewage Treatment Works). In future, it is likely that schemes which make space for water (including those which involve beavers) may be funded through Defra’s Environmental Land Management Schemes. www.pooleharbourcatchment.co.uk | [email protected]

Winter Newsletter 2019/20

Aly Maxwell Aly Management and costs– cont’d The cost of beaver projects is likely to be met through charitable donations. If beavers are to be a long-term tool, then their management would need to be included in the overall financing for the restoration and effective management of our rivers and water habitats.

The PHCI advocates full stakeholder involvement and supports the recommendations from the River Otter trial that any proposed beaver site (whether planned or potentially colonized over time) must conform to the following four fundamental landscape planning principles: • Identification of where beavers can be tolerated, can provide valuable wildlife, water quality and natural flood defence benefits and where conflicts are unlikely. • Identification of risk zones where beavers may be tolerated but conflict is likely, and a management regime will be necessary (e.g. Water Recycling Centres/ urban areas). • Identification of- no go areas and/or areas where beavers will not be tolerated (e.g. flood embankments, pumped landscapes, low-lying arable and horticultural landscapes). • No beavers to be reintroduced unless this prior broad assessment has been done (see R. Otter study, ref below). Beavers arouse a great deal of interest from the public and have increased visitor interest in Devon. Whilst this helps bring business and potentially funding for their management, it also means that any trapping and relocation will need to be handled sensitively.

Can beavers be released in Dorset? At present, beavers may be released into secure enclosures subject to a licence from Natural England and consultation with local landowners. A wider release would also need to be licensed, with more extensive local consultation. Wild releases are likely to depend on the outcomes of the River Otter trial which was reported to Government in February 2020, for decisions on their retention or removal, and recommendations for management. This may take six months and, in the meantime, projects are under development by partners in Purbeck (wild release led by the National Trust) and in the Dorset Frome headwaters (Enclosed research study led by Dorset Wildlife Trust). PHCI partners have convened a Dorset Beaver Working Group to promote the wider consultation on the re-introduction of beavers in the Poole Harbour catchment and to ensure the development of a suitable county-wide management plan prior to any open releases. Where can I learn more? Where can I learn more? www.dorsetwildlifetrust.org.uk/BeaverAppeal The Eurasian Beaver by R Campbell-Palmer National Trust: [email protected] Saving the dammed by E Wohl www.devonwildlifetrust.org/devon-beavers-2020 Eurasian Beaver Handbook by R Campbell-Palmer, www.scottishwildbeavers.org.uk D Gow, R Needham, S Jones & F Rossell www.beavertrust.org