Beavers in Scotland: consultation on the strategic environmental assessment

5. Environmental assessment mitigation

Section 4 sets out how beavers can have a wide range of interactions with both the natural and the human environment. Beavers are often described as a keystone species because of their ability to influence and shape their environment. This ability to alter the environment, either natural or man-made, is one of the reasons that may bring beavers into conflict with people. Although conflict with human land uses such as for agriculture, fisheries, property and infrastructure is likely to be the main driver for management intervention, there may also be a need to manage beavers and their impacts for other reasons, for example to protect the natural heritage or prevent the spread of animal diseases. The environmental assessment in section 4 identified instances where the creation of beaver dams has the potential to negatively affect a biological receptor. The mitigation measures outlined below will address impacts on the natural heritage as well as conflicts with human uses and disease spread.

Across the beaver range, whether in Europe, Asia or North America, a wide variety of techniques has been developed either to manage the impact of beavers or to directly manage the animals themselves. Some of this has been summarised in "The Eurasian Beaver Handbook, ecology and management of Castor fiber" (Campbell-Palmer et al. 2016). This helps to demonstrate that mitigation measures are already well-established and being practiced and therefore can be feasible and straightforward when applied in the Scottish situation. Existing literature reviews of the effectiveness of mitigation measures are being complemented by experience from trialling of different solutions/techniques in Tayside.

In the Scottish context the aim is to establish approaches that will avoid potential damage and then, where it occurs, to mitigate as appropriate. A Scottish Beaver Forum has been established by SNH and the membership includes non-government conservation bodies, land use and fishery bodies, and government agencies. Proposals for managing the impacts of beaver will be developed in consultation with this Forum to produce a management framework. The framework will include guidance on adaptive management, mitigation techniques, deterrence and exclusion, species licencing, positive management options, beaver welfare and provision of an SNH advisory service.

5.1 Mitigation hierarchy

The mitigation of impacts arising from the activities or presence of beavers range from practical measures to manage the local environment that influence the behaviour of beavers, mitigating the damage, through to the trapping and removal of animals or their lethal control. These are considered below in an environmental assessment mitigation hierarchy.

5.2. Avoidance of detrimental impacts

Positive and adaptive conservation management to enable beavers to establish and remain, and to reduce the potential for conflict with some types of land management. This management would likely be promoted on land owned by nature conservation or government agencies or through positive incentive schemes. It also provides wider environmental benefits. Positive measures could include the following:

• allowing some land to revert to wetlands, retention of existing wetlands
• 20 - 50m wide riparian buffer zones - woodland creation and restoration
• flood attenuation schemes
• flood-bank re-alignment

5.3 Mitigation techniques

A large number of mitigation techniques could apply to the two policy areas to reduce the impact of beaver activity. These relate to dam building, burrowing and foraging. The decision as to which technique(s) is most appropriate will depend on site-specific conditions. Consideration will also be needed to address, for example, animal welfare, legal and regulatory implications which may be relevant to beavers themselves or other protected species.

5.3.1 Dam-building

As has been discussed in sections 3.4.3 and 4.1, beavers building dams on rivers may bring a range of benefits. It is also important to accept that beaver dam-building will sometimes conflict with human interests and impose a cost in terms of resources (including time and money), especially in intensively managed landscapes. There is a particular issue over the possible effects of beaver dams on the movement of migratory salmonids under certain conditions ( section 4.2), and a question as to whether this may indirectly affect other species such as otter that will sometimes feed on them ( section 4.8).

Dam-building and the incidence of dams varies depending on habitat characteristics. On lochs or rivers more than 6 m wide, dam-building is uncommon. Beavers utilising narrower water bodies (less than about 6 m wide and 0.8 m deep) often build dams and can create extensive systems of multiple dams and impoundments. Where watercourses are steeper in gradient with higher banks in narrow valleys, the capacity for beaver activity to alter or create habitats on a significant scale is much more limited.

The length of time that dams persist in the environment varies and can be relatively short lived, particularly if food resources become depleted and/or they are not worth maintaining compared with the costs and benefits of exploiting resources elsewhere.

A summary of those management techniques used to mitigate the impacts of beaver damming activity is provided in Table 5.3.1 below.

Table 5.3.1: Summary of measures to mitigate impacts from the dam-building activities of beavers

	Summary of technique	Purpose	Limitation
Dam-notching	Removal of a small section of beaver dam, usually by hand, to increase water flow over that section	Most often associated with aiding fish passage. May be used to lower water levels in beaver ponds behind a dam.	In active territories, beavers will often repair notched dams within 48 hours. Labour intensive, especially at a catchment scale.
Flow devices	Placing a pipe through a dam to manage the water level behind it on a permanent basis	Used to manage water level behind or above a dam where a certain water level is tolerable, but any further increase would not be. Essentially, it acts as an overflow device for the dam.	Can be time consuming to install. Unlikely to be effective if poorly installed or the pipe is sized wrongly. Generally ineffective if less than 0.8 m of water remains behind the dam. Requires some ongoing maintenance.
Dam removal	Removal of a dam, either by hand or using mechanical devices	Used where no increase in water level, or potential blockage to fish passage, is considered acceptable in a watercourse or part of a watercourse.	Removal of dams often stimulates beavers to rebuild the structure using fresh woody material. Likely to require repetition. Manual removal may be more time consuming than using heavy machinery, but less likely to result in sudden release of water and/or silt.
Discouraging	Use of dissuasive techniques to prevent dam-building either where known 'pinch points' occur or where a dam has been removed and is likely to be reconstructed	Prevention of dam-building or rebuilding where dam-building is deemed intolerable.	A range of techniques have been trialled and found ineffective. Might include electric fencing strung above the dam site. Flashing lights etc. may work until animals become habituated to them.
Grilles	Use of metal grilles to prevent access to certain types of likely damming points, such as culverts	Prevents access for beavers to dam natural pinch points in watercourses.	Easily blocked by debris from beaver activities upstream or general detritus. Requires regular clearance and monitoring.

5.3.2 Burrowing

Beavers are strong and able diggers, and can readily excavate burrows and canals, which may collapse and/or increase bankside erosion to varying extents, depending on associated water flow and substrate type. Beaver burrows tend to be large and can end in sizeable chambers. Although the route of these structures is occasionally visible, the position of many others is difficult to determine. Beavers will readily excavate burrow systems which begin under water with entrances which can be obscured by tree roots or vegetation. Although the actual instances of beaver burrows causing the collapse of engineered flood walls are few, European natural resource agencies have developed a range of remedial measures. Other concerns relate to the possibility of livestock, horses, humans or farm machinery breaking through the surface into a beaver burrow with resultant damage or injury.

A summary of those management techniques used to mitigate the impacts of beaver burrowing activity is provided in Table 5.3.2 below.

Table 5.3.2: Summary of management techniques used to mitigation beaver burrowing activity

	Summary of technique	Purpose	Limitation
Prevention of burrowing	Use of sheet metal piling, rock armour or mesh to prevent burrowing, or further burrowing, into vulnerable flood defences or adjacent land.	Prevents beaver burrowing activity from starting or continuing in new or remodelled flood banks or into adjacent land.	Not straightforward or cheap. Can have considerable hydrological or hydrogeomorphological impacts. Likely to displace activity rather than completely prevent it.
Realignment of flood banks	Expanding the riparian zone used by beavers by moving existing flood defences a minimum distance (in the region of 20 m) from the edge of a watercourse.	Reduces the likelihood of beaver activity in flood defences or productive land. Allows for a greater floodable area within a catchment and may provide wider opportunities for riparian habitat creation and restoration and flood management.	Loss of productive land. Not all areas have sufficient room for expansion. Likely to be significant resistance from some stakeholders. Expensive.

5.3.3 Foraging activity

Beavers are herbivores and will readily consume a wide range of bark, shoots and leaves of woody (primarily broadleaved species), herbaceous and aquatic vegetation. Whilst beaver foraging activity is most noticeable on trees and woody vegetation, beavers will also forage in crops both as a source of food and for construction material where there is limited woody material available. Beavers display regular routines and feeding patterns, resulting in well-worn trails and canals being easily visible.

A summary of those management techniques used to mitigate the impacts of beaver foraging activity is provided in Table 5.3.3 below.

Table 5.3.3: Summary of management techniques used to mitigation beaver foraging activity

	Summary of technique	Purpose	Limitation
Exclusion fencing	Fencing, either permanent or temporary, to prevent beavers accessing areas of water, crops or trees where damage is deemed intolerable.	Prevents beaver access to areas where their impacts cannot be tolerated or prevents beavers accessing vulnerable or valuable crops or trees.	Not suitable for extensive areas. All fencing requires maintenance. Fencing to prevent the movement of beavers along a waterway may provide a dam-building point or act as an impediment to the movement of fish and other species. Inappropriate fencing could exclude other grazing/browsing species with consequent impacts on habitats. Probability of displacing impacts.
Individual tree protection	Protection of individual or small numbers of amenity or other valuable trees by use of individual fences, mesh wrapping or deterrent paints	Prevents beavers foraging on individual trees.	Relatively high visual impact. Only suitable for small numbers of trees.

5.4 Management of beavers - physical removal and exclusion

In cases where beaver conflicts cannot be suitably managed, because costs are too high or potential impacts too great, their removal or complete exclusion may be the only practical solution. These options would be more highly regulated and most would require an SNH licence as well as having to address other regulatory regimes. Methods of regulating beaver populations could include the following:

• Trapping and removal - live trapping by authorised persons for transport and release at approved sites
• Lethal control - authorised persons to kill specified beavers
• Lodge destruction - destruction of burrow/lodge by infilling or flattening
• Exclusion - for example from areas of prime agricultural land, designed gardens, road culverts and waste water treatment works. There may be some sub-catchments where effective fencing can exclude beavers from areas where consistent and constant removal may be the only other alternative.
• Fertility control - may allow for retention of stable but non-breeding beaver populations but there is little knowledge of the efficiency

5.5 Compensatory measures

Where mitigation measures are not feasible and there is beaver damage, e.g. to aspen and other vulnerable tree species, then biodiversity net gain should be considered such as compensatory planting elsewhere which is less susceptible to beaver activity. The limitation is that this approach would not always be able to address the loss of certain key habitat features, such as woodland of a particular structure and age, and the species associated with such features.

5.6 Pathogen / Disease transfer

In addition to mitigation measures to reduce the impact of beaver activity, it may be necessary to address the potential risk of disease transfer. The risk of spreading diseases associated with beavers is considered to be low, however surveillance should continue. In addition, any imported animals will be quarantined and screened. Table 5.1.4 below provides a summary of those mitigation measures identified to reduce this risk of disease transfer.

Table: 5.6.1: Summary of mitigation measures to reduce the risk of disease transfer

Pathogen/disease identified in assessment with risk of transfer to human populations	Mitigation identified
Alveolar hydatid tapeworm Echinococcus multilocularis	Health assessment and pathogen screening before release of any further beaver - use of diagnostic test of live animals and serological screening
Tuaraemia ( Francisella tularensis)	Health assessment and pathogen screening before release
Leptospira spp.	Continued health surveillance of both beaver populations
Cryptosporidium spp.	Enhanced surveillance of human cases for a set period; Approaches to be discussed and agreed with local authority environmental health teams and Scottish Water
Giardia duodenalis	Continued health surveillance of both beaver populations. Enhanced surveillance of human cases for a set period; Approaches to be discussed and agreed with local authority environmental health teams and Scottish Water.

5.7 Management measures

Management of beavers and their impacts will involve the interaction of a number of different pieces of legislation. Further advice for mangers will be required. The following information, support and guidance have already been identified, as presented in Table 5.1.5 below:

Table 5.7.1 summary of mitigation advice, support and guidance

Mitigation Measure	Purpose	Lead Authority	Proposed Timescale
Guidance	Disseminate information on appropriate techniques to manage for the presence of beavers, or eliminate or reduce unwanted impacts e.g. tree protection	SNH	Available when legal protection enacted
Stakeholder forum	Set up and support appropriate a stakeholder group to facilitate knowledge exchange and communication	SNH	Ongoing
Best practice including training	Publication of information and provision of training for staff of public bodies, key stakeholders, consultants (e.g. through CIEEM)	SNH	Some ongoing activities, SNH Sharing Best Practice event(s) in 12-24 months from legal protection.
Trial mitigation techniques	To test efficacy and applicability and cost of management techniques e.g. exclusion fencing, fish passes	SNH	Ongoing
Advisory service	One to one advice to affected parties on the reduction or elimination of unwanted impacts.	SNH In due course, private operators will provide advice	Available now from SNH
Licensing scheme	Development of a fit-for-purpose scheme of appropriate derogations to enable legal management that can reduce or eliminate impacts from beaver activity	SNH	Available when legal protection enacted
Animal health monitoring and quarantine	To prevent the introduction of harmful biological pathogens into Scotland, and monitor existing populations if judged appropriate	SG	To be decided for existing beaver populations that have already been monitored. Also would be required for any future, approved importations