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Publication - Consultation Paper

Beavers in Scotland: consultation on the strategic environmental assessment

Published: 12 Dec 2017

A consultation on the policy to reintroduce beavers to Scotland and the strategic environmental assessment of this policy.

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170 page PDF

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Contents
Beavers in Scotland: consultation on the strategic environmental assessment
4.11 Beavers and Fish

170 page PDF

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4.11 Beavers and Fish

Our native freshwater fish can be broadly separated into diadromous and freshwater-resident species. Fish which are diadromous (i.e. migrate between fresh water and the sea to complete their life cycle) include Atlantic salmon, trout (as sea trout), European eel, brook, river and sea lamprey, sparling and the shads. Those species that, in Scotland, are found only in fresh water are Arctic charr, powan, vendace, pike, roach, perch, minnow and stone loach. Three- and nine-spined sticklebacks can utilise both freshwater and marine habitats.

All species, regardless of whether they are diadromous or freshwater-resident, may undergo migrations at some period within their life history. These movements may be ontogenetic (e.g. based on life stage) changes in habitat use, or migrations may be undertaken to allow fish to fulfil a specific function, such as spawning. Some species, such as freshwater-resident trout, and in some cases Arctic charr, may undertake movements from lochs to riverine spawning areas. Others, such as pike, roach and perch, may undertake migrations to particular habitats within lochs or large rivers to spawn. The timing and location of these movements varies significantly between species.

A summary (see Table 4.11.2) of the potential interactions between beavers and fish is presented below; where possible these have been attributed to a neutral, positive or negative effect.

4.11.1 How beaver activity affects fish

This complex ecology, as described above, means that many of our native fish species have the potential to interact with beavers and, in fact, these fish will have co-existed with beaver for millennia prior to their extinction in Scotland. Table 4.11.1 provides a summary of the perceived positive and negative impacts of beavers on fish derived from the published literature during a recent major review. The scale and direction of impact of beavers on fish will differ according to the species concerned and its ecology.

Table 4.11.1: Summary of the perceived positive and negative impacts of beavers on fish.

Positive impacts

Negative impacts

Enhanced habitat availability / complexity

Barriers to fish movement

Enhanced over-wintering habitat

Reduced spawning habitat

Enhanced rearing habitat

Altered temperature regime

Provision of cover

Reduced oxygen levels

Enhanced diversity/ species richness

Reduced habitat quality

Enhanced abundance / productivity

Altered flow regimes

Provision of habitat under low flows

Loss of cover

Provision of high flow refuge

Reduced productivity

Provision of temperature refuge

Reduced growth

Enhanced water quality

Abandonment of better settlements

Sediment trap

Reduced water quality

Enhanced invertebrate productivity

Enhanced growth rates

Enhanced fish condition

Provision of fishing areas

4.11.2 Evidence of beaver fish interaction

Eurasian beaver would have co-existed with native fish fauna in Scotland for millennia before the former species was extirpated. The absence of Eurasian beaver from the Scottish fauna for the last 500 years means that, prior to the SBT, nothing was known about the impact of this species on Scottish freshwater fish. The range of interactions, positive as well as negative, could, however, be inferred from the published work available before the trial.

Two SNH-commissioned reviews of the impacts of beaver on a variety of fish species have been carried out and these, together with more recently published data, were considered by the Beaver-Salmonid Working Group ( BSWG).

Much of the published literature on the impacts of beavers on freshwater fish originates from North America and relates to the activities of the North American beaver. Far fewer data are available on the impact of Eurasian beavers on European fish species or fish communities. Some concern has been expressed about the extrapolation of data gathered relating to the impact of the North American beaver on fish to the European (or Scottish) situation, largely because of differences in habitat typology and dissimilarity in the range of species concerned, including salmonids. Regardless of these differences, the recent SNH review and the BSWG concluded that, in general, issues such as the removal of riparian vegetation and tree cover; ponding; inundation and impacts on sediment transport as a result of beaver dam construction; and hydrological alterations and their influence on fish migration can be considered to be impacts common to both species.

Eurasian beavers co-exist with fish throughout their geographical range. However, in areas such as Denmark, Finland, France, Norway and Sweden and some Baltic states, where beavers co-exist with high economic value species such as Atlantic salmon, there is surprisingly little published information relating to beaver-salmonid interactions. The information available has been reviewed within the BSWG report. Data relating to other, non-salmonid, species are also limited.

The conclusions reached in the available studies are mixed. This is also complicated by the fact that some of the data available come from areas where beavers have been reintroduced and management is varied. In Lithuania, where beavers were reintroduced in 1947, it has been recommended that beaver dams in the middle and lower reaches of trout-spawning streams should be removed to reduce impacts on spawning trout. In Scandinavia, where Atlantic salmon and beaver are both native, beavers have been actively managed for centuries and there is little published evidence of negative impacts.

Table 4.11.2: Summary of potential interactions between beavers and fish.

Activity

Mechanism

Positive effects

Negative effects

Notes

Felling

Change in riparian woodland: Opening of woodland canopy and increased patchiness

  • Increased light penetration may lead to increased production within streams, ponds and lochs. Increased primary productivity and temperature may increase production of aquatic macroinvertebrate prey items for fish. This could lead to increased fish productivity and improved individual growth rates
  • Increased temperatures may favour the establishment of non-salmonid species which have a higher tolerance to lower dissolved oxygen concentrations (such as cyprinids and sticklebacks)
  • Increased light may lead to the establishment of macrophyte communities, creating complex habitats that offer shelter to some fish species (such as pike, perch, roach and sticklebacks) and their prey
  • Penetration of light to the riparian zone may result in the development of plant communities that will stabilise banks, reduce erosion and provide increased opportunities for greater terrestrial input of food items for fish
  • Reduction in shading has the potential to increase water temperature and result in increased thermal stress upon some fish species, particularly salmonids
  • Increased temperatures may favour the establishment of fish species which may compete with, or predate, salmonids
  • Increased temperatures can contribute to reduced levels of dissolved oxygen in some circumstances. This may be unfavourable for some fish species (such as salmonids)

Tree-felling may also undo some of the extensive tree-planting restoration work that has taken place in some catchments (particularly the upper areas of catchments, which have little natural tree cover)

Felling

Change in riparian woodland: Change in relative abundance of different tree species

  • Possible changes in the amount of allochthonous material derived from different sources (principally leaf litter), which may benefit some aquatic macroinvertebrates and potentially the fish which prey on them
  • Possible reduction in type and quantity of allochthonous material (principally leaf litter) may lead to a reduction in aquatic macroinvertebrate community composition and production. This may negatively affect fish which prey on them
  • Possible reduction in the quantity of terrestrial (invertebrate) prey items that enter the aquatic environment as food for fish

Felling

Change in riparian woodland: Change in age classes of trees

  • Possible changes to tree age class in riparian or littoral areas may result in a more open canopy and increased light penetration, with consequent benefits for some species (see above)
  • Loss of mature woodland may result in lesser quantities of allochthonous material entering waterbodies. This can affect macroinvertebrate production and therefore the production of fish
  • Possible reduction in size and quantity of large woody debris entering the watercourse in the longer term may affect in-stream habitat structure, and this may adversely affect some fish species
  • Possible changes to tree age class in riparian or littoral areas may result in a more open canopy and increased light penetration, with consequent negative effects for some species (see above)

Effects will depend on nature of changes, and the extent to which trees affected by beavers regrow. See Annex 1 Table 3.4.1 for beaver effects on woodland trees

Felling and constructions

Changes in amount/diversity of woody material in watercourses

  • Greater quantities of large wood items in streams, rivers and lochs can result in increased habitat diversity and an increase in the availability of prey items and fish cover
  • Where large woody debris occurs, it may reduce the transport of sediment downstream
  • The establishment of large log jams could hinder the in-stream movement of some fish species if they act as barriers
  • Depending on where woody items aggregate, such material can act as a barrier to movement or result in the loss of habitat
  • Where the quantity of large and small woody items is too great, this may result in blockages which may affect the transport of important gravels

Feeding

Feeding on specific terrestrial herbaceous and aquatic plant species

  • Changes to macrophyte community structure may favour some species of (non-salmonid) fish and their prey
  • Decrease in macrophyte species in some lochs may have a negative impact on species that depend on them for food or shelter. Pike, for example, are often associated with macrophytes because they use these as cover when ambushing prey. Roach and perch may utilise macrophytes as cover from pike. Salmonids are rarely associated with macrophytes

See Annex 1, Table 3.7. for a summary of beaver effects on aquatic plants

Dams/pond creation

Change from lotic to lentic habitat

  • Increase in habitat diversity, which may favour some fish species or fish life history (ontogenetic) stages. In some situations this may also result in an increase in species richness - of both fish and invertebrate prey items
  • Increased temperatures, changes in habitat availability and feeding opportunities in lentic habitats may result in increased individual growth rates, fish condition and overall production
  • Depending on depth and location, impoundments may offer a high-temperature refuge for some fish
  • Increase in habitat diversity for fish may favour some species over others, or benefit only some life history stages (e.g. juvenile or adult fish)
  • Depending on location, the creation of lentic habitats may result in habitat loss for species which favour or dominate lotic habitats
  • Accumulation and smothering of bed sediment upstream of dams, and a reduction in habitat quality for some species (principally salmonids)
  • Reduction in turbulence (or mechanical mixing) may occur upstream of dams, resulting in a reduction in dissolved oxygen
  • Possibility of increased opportunities for fish predators (e.g. piscivorous birds, mammals such as otter, or man)

Dams/pond creation

Change in hydrological processes on riparian and downstream habitat

  • Reduction in the transport of fine material may improve the quality of spawning and rearing habitats downstream of any impoundment
  • Impoundments may create low- and high-flow refuges for fish
  • Flooding of riparian and wetland habitats can provide spawning opportunities for species such as pike and additional habitat for species such as European eel
  • Changes in flow may result in sediment starvation in gravel spawning areas. This can affect both salmonids and spawning lamprey
  • A reduction in flow downstream of the structure may result in a reduced wetted width and a loss of juvenile fish habitat

Dams/pond creation

Changes in water quality downstream

  • Reduction in the amount of fine material deposited on the stream or riverbed downstream of the impoundment. This may result in an improvement in the quality of gravel spawning areas (downstream) for salmonids and lamprey
  • Accumulation of fine sediments may increase the volume of available habitat for lamprey ammocoetes

Dams/pond creation

Impacts on movement of species

  • Prevention of the free movement of fish to all habitats required during their life cycle. This is particularly relevant to key migration periods (such as spawning migrations), but also at other times
  • The scale of impact may be greater for species which have a limited ability to overcome in-stream obstacles (such as lamprey)

Other

Fisheries

  • Beaver habitats (impoundments and flooded wetlands) may benefit North American signal crayfish, an invasive non-native species, if these are present within the catchment

Indirect habitat creation/restoration initiatives as result of beaver presence

Beaver used to promote opportunities for riparian and freshwater habitat creation/restoration

  • Presence of beaver may act as an incentive for greater investment, management and monitoring. This could include those related to the restoration and management of riparian woodland
  • Beaver presence may eliminate fish-related riparian woodland restoration activities that are currently under way

4.11.2 Distribution of fish in the beaver policy area

The following section concentrates on those fish of conservation importance that are likely to overlap with core beaver woodland and as such maybe positively or negatively affected by beaver activity.

The potential overlap between beaver habitat and Atlantic salmon is described in section 4.2 of the Beavers in Scotland Report (see Annex 1). Dam-building activity will not occur in the downstream, wide and deep river sections of the Tay catchment, and indeed it is unlikely in much of the higher reaches where potential beaver habitat does not occur ( Annex 1, section 4.2). However, dam- building and other beaver activity will continue to expand throughout the Tay catchment as the population increases and spreads ( Annex 1, section 3.2).

4.11.2.1 Fish of conservation importance

To determine whether the activity of beavers on (native) fish species is significant in the context of this Strategic Environmental Assessment, the assessment of impacts (positive and negative) has focussed on those species for which beaver activity may affect directly or indirectly (as discussed above), which are considered as having conservation importance and as such are afforded European or national protection wherever they occur.

Table 4.11.3 below therefore identifies those fish of conservation importance that utilise 'potential beaver core woodland' (as described in section 4.1 of this report) and are found within the beaver policy areas.

Table 4.11.3: Summary of fish of conservation importance within the beaver policy area that overlap with potential beaver core woodland

Fish species

Conservation importance

Atlantic salmon

River Dee SAC
River South Esk SAC
River Spey SAC
River Spey SSSI
River Teith SAC
River Tay SAC

Sea lamprey

River Tay SAC
River Teith SAC
River Spey SAC
River Spey SSSI

River lamprey

River Tay SAC
River Teith SAC

Brook lamprey

River Tay SAC
River Teith SAC

4.11.3 Assessment of likely effects on fish of conservation importance in the beaver policy area

Each of the fish species identified in Table 4.11.3 above are discussed in turn below in the context of those effects (positive or negative) that have been identified as a result of beaver activity. Where this relates to a species included in the Habitats Regulation Appraisal of the policy, a summary of the advice from SNH, provided to inform an appropriate assessment ( AA) of the policy with respect to SAC sites (see Annex 2 for the full advice) has been used (referred to hereafter as ' SNH HRA advice'). For the purpose of this assessment, the concluding points of the SNH HRA advice have been replicated where appropriate for each species. Assessment of other fish species (i.e. SSSI notified features), has been made in the context of the SNH HRA advice in combination with knowledge of the individual sites and their condition. Where mitigation or monitoring may be appropriate, this has been identified in the narrative. Further discussion relating to the management of beavers including mitigation and monitoring options is provided in section 5 and 7 respectively.

For species and habitats of conservation interest in the wider countryside there will be an ongoing need to assess data derived from general surveillance and monitoring activities that are already in place, and intervene with management if and when necessary. This will be informed by a more strategic approach to management being developed in due course.

4.11.3.1 Consideration of potential positive effects on fish of conservation importance

All Fish Species

The anticipated positive effects of beaver activity for the aforementioned fish species of conservation importance are discussed below in general terms. There is a role for further monitoring at each of the designated sites identified in Table 4.11.3 above, to assess such effects via the SCM process - further narrative is outlined in section 7 of this report.

Beaver foraging activity

Through foraging activity, beavers are able to change the structure of riparian woodland (see section 4.2), impacting on the amount of open canopy or age class of tree species or abundance of particular trees through their preference for certain tree species against their relative abundance. These changes can bring about positive effects for prey species or terrestrial input of food items and can creates suitable shelter areas for fish and their prey species to hide and rest. These indirect effects from changes to woodland habitat can be summarised as:

  • Increased light penetration may lead to increased production within streams, ponds and lochs. Increased primary productivity and temperature may increase production of aquatic macroinvertebrate prey items for fish. This could lead to increased fish productivity and improved individual growth rates
  • Increased light may lead to the establishment of macrophyte communities, creating complex habitats that offer shelter to some fish species (such as pike, perch, roach and sticklebacks) and their prey
  • Penetration of light to the riparian zone may result in the development of plant communities that will stabilise banks, reduce erosion and provide increased opportunities for greater terrestrial input of food items for fish
  • Possible changes in the amount of allochthonous material derived from different sources (principally leaf litter), which may benefit some aquatic macroinvertebrates and potentially the fish which prey on them

Beaver foraging on tree species creates woody debris that finds its way into streams, rivers and lochs either being abandoned after feeding or through creation of food caches for the winter. This has a number of indirect effects for fish, summarised as:

  • Greater quantities of large wood items in streams, rivers and lochs can result in increased habitat diversity and an increase in the availability of prey items and fish cover
  • Where large woody debris occurs, it may reduce the transport of sediment downstream

While beaver predominately feed on woody stems they also forage on herbaceous and aquatic plant species, the impact of which can benefit fish:

  • Changes to macrophyte community structure may favour some species of (non-) fish and their prey

Beaver damming activity

The creation of beaver dams across a stream or river (<6m diameter) changes the habitat from a running water to one that is still. This change adds habitat diversity to the river or stream which can provide in case situations benefits to fish and prey species. It also brings about a change to the environmental characteristics of the stream or river which can provide refuge for some fish or benefit growth rates. These effects from be summarised:

  • Increase in habitat diversity, which may favour some fish species or fish life history (ontogenetic) stages. In some situations this may also result in an increase in species richness -of both fish and invertebrate prey items
  • Increased temperatures, changes in habitat availability and feeding opportunities in lentic habitats may result in increased individual growth rates, fish condition and overall production
  • Depending on depth and location, impoundments may offer a high-temperature refuge for some fish

Dams can also exert an effect on the hydrological processes of the river or stream, affecting the sediment transport and water quality as well as potentially creating new habitat available for fish, these indirect effects can be summarised:

  • Reduction in the transport of fine material may improve the quality of spawning and rearing habitats downstream of any impoundment
  • Impoundments may create low- and high-flow refuges for fish
  • Flooding of riparian and wetland habitats can provide spawning opportunities for species such as pike and additional habitat for species such as European eel
  • Reduction in the amount of fine material deposited on the stream or riverbed downstream of the impoundment. This may result in an improvement in the quality of gravel spawning areas downstream) for salmonids and lamprey
  • Accumulation of fine sediments may increase the volume of available habitat for lamprey ammocoetes

Evidence from elsewhere in Europe

The table below (Table 4.11.4) provides a summary of impact of beavers on fish species of conservation importance, taken from studies in Norway (Atlantic salmon) and Denmark (brook lamprey) showing either a positive or neutral effect. The fish population monitoring carried out through the SBT at Knapdale did not feature Atlantic salmon or lamprey species.

Table 4.11.4: Summary of impact of beavers on fish species of conservation importance.

Species

Overview

Atlantic salmon

Dam construction led to the loss of some spawning habitat due to the siltation of gravels. Juvenile Atlantic salmon were found above dams. Authors state that while the hypothesis that beaver dams have had no impact on Atlantic salmon cannot be supported, neither can the view that fish are unable to negotiate beaver dams.

Beavers constructed five dams which had the potential to prevent access to spawning areas. While there is the potential to negatively affect upstream and downstream migration of Atlantic salmon, the actual impact may be negligible due to the low frequency, small size and short lifetime of dams. The length affected was minor, but tree-felling resulted in a loss of shade over a greater area. There has been a simultaneous increase in beaver population size and Atlantic salmon catches over a 40-year period.

Brook lamprey

Dams are a complete barrier to brook lamprey, but they will not have an overall negative effect on this species.

Lastly, the presence of beaver may act as an incentive for greater investment, management and monitoring. This could include those related to the restoration and management of riparian woodland with associated benefits to fish species.

4.11.3.2 Consideration of potential negative effects on fish of conservation importance

Atlantic Salmon

Atlantic salmon are widely distributed across Scotland and within the network of Atlantic salmon SAC's. However, when considering the viability of individual populations it is important to consider the complex nature of Atlantic salmon populations within UK rivers. Stock structure can, for example, incorporate a variety of discrete populations each of which are adapted to complete their life history within certain geographical areas of a catchment. The time taken to smolt, the timing and duration of the smolt migration, time spent at sea and timing of return may all have a genetic basis. In terms of location, it is widely accepted that early running multi-sea-winter fish (known as the Spring stock component) tend to spawn in the upper catchments of rivers, and that late-running fish (Autumn spring stock component) may ultimately spawn in the lower reaches of river systems. Whilst this may be a simplistic view, it demonstrates that Atlantic salmon can, and often do, utilise the entire catchment during spawning time and for the production of juvenile fish.

The Spring stock component typically spawns in the upper reaches of rivers, and damming activity in areas downstream of such areas may have a negative impact on this portion of the Atlantic salmon stock. This life history type, which is included as a reason for selection in many Atlantic salmon SACs, has undergone a long-term national decline and remains a key issue for those involved in the maintenance of Atlantic salmon fisheries, as well as SNH. The resilience of migratory Atlantic salmon populations to new pressures is an issue that must be considered in respect of how beaver-salmon interactions are managed.

Knapdale

There are no sites in Knapdale designated for Atlantic salmon.

Tayside

  • River Dee SAC
  • River South Esk SAC
  • River Spey SAC
  • River Spey SSSI
  • River Teith SAC
  • River Tay SAC

SNH HRA advice

Eurasian beaver have the potential to impact Atlantic salmon populations within all of the affected, or potentially affected, SACs, listed above. Beaver activity may be restricted to certain areas of the catchment (with river width <6 m and presence of potential core beaver woodland) but the locations of impacts may be coincident with vulnerable life history types of Atlantic salmon (the 'Spring' stock component).

The building of dams in areas where river widths are <6m may have a particularly significant impact on the Spring stock component, or other fish which spawn in river tributaries which are narrow (i.e. <6m). Even if a dam does not form a complete barrier to upstream Atlantic salmon movement, delays caused by such an obstruction can increase the probability of predation, result in a loss of fish condition, and delay movement to a point where low water temperature becomes a physiological constraint. Barriers may also slow or prevent the movement of juvenile Atlantic salmon as they occupy all areas of suitable habitat, or impact the downstream movement of smolts.

To maintain the distribution of Atlantic salmon into such areas it is important to ensure that the passage of fish past any barrier is assured. This may be achieved through the easement or removal of barriers at certain times of year (e.g. during spawning time) or through the installation of devices such as flow management devices. However; it is unclear whether such a device could be used to assist the upstream migration of large Atlantic salmon (which is typical of 'Spring' fish) as it has not yet been scientifically tested in Scotland this regard.

Barriers and other in-stream/riparian beaver activities may impact sediment transport within rivers and streams, either directly or by influencing the hydrology of affected watercourses. This can negatively impact the replenishment of Atlantic salmon spawning areas.

SNH HRA advice conclude that there is the potential for beavers to have an adverse effect on site integrity of the SACs designated for Atlantic salmon through dam-building activities and other related activities. Mitigation to avoid these impacts is necessary. It is important to ensure that the passage of fish past any barrier is assured (this precautionary approach is currently needed due to the existing lack of understanding of the full details of any potential impacts on the SACs).

SSSI Assessment

Impacts to sea lamprey in the River Spey SSSI are likely to be similar to those described above for the River Spey SAC. There is therefore potential for beaver activity to adversely affect the natural heritage interest of national importance.

Mitigation

Mitigation to ensure passage may be achieved through the easement or removal of barriers at certain times of year important for salmon (i.e. during spawning and smolt emigration) or through the installation of flow control devices. However; it is unclear at this time whether flow control devices could be used to assist the upstream migration of large Atlantic salmon (which is typical of 'Spring' fish). If a beaver dam might cause an adverse effect on the integrity of the SAC and a flow control device might not allow passage upstream, then alternative mitigation measures which will allow passage must be put in place. These mitigation measures should be included in a Beaver Management Plan for the individual SACs, which should also set out in what circumstances there could be an adverse effect on site integrity, and a framework through which to implement any mitigation measures should they become necessary.

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.

Brook, River and Sea Lamprey

Little is known about intraspecific variation within lamprey species, although anadromous forms are not considered to 'home' to their natal streams in the same way as Atlantic salmon do. However, the distribution of lamprey within catchments does differ according to species: with Brook lamprey being more widely distributed within catchments, while Sea lamprey are typically found in the lower reaches of rivers, and River and Brook lamprey are more closely associated with the middle and upper catchment. Whilst most attention has focussed on upstream migrating adult fish, both Sea and River lamprey may spend significant time in areas affected by beavers prior to migrating to sea.

Knapdale

There are no sites in Knapdale designated for lamprey species.

Tayside

Sea lamprey

  • River Tay SAC
  • River Teith SAC
  • River Spey SAC
  • River Spey SSSI

River lamprey

  • River Tay SAC
  • River Teith SAC

Brook lamprey

  • River Tay SAC
  • River Teith SAC

Assessment

Eurasian beaver have the potential to impact lamprey populations within all of the potentially affected SACs through dam building restricting their movements. However, given the distribution of anadromous lamprey (particularly Sea lamprey) within river catchments where they are often restricted to the lower reaches of rivers and mainstems, the potential for impact by Eurasian beaver is not as high as it may be for Atlantic salmon. For instance Sea lamprey surveys have only ever found this species in rivers wider than 6m which means they are largely found outwith areas of beaver dam building activity.

The potential overlap with Brook lamprey, and to a lesser extent River lamprey, requires more consideration. Brook lamprey is not anadromous and remains in freshwater for its entire life cycle. Little is known about its movement within river systems, although it is clear that the species is mobile enough to utilise all available habitats within a river system. In the River Tay SAC Brook lamprey have a wider distribution than the other two species. Research in Denmark suggests that whilst dams are a complete barrier to Brook lamprey, they did not have an overall negative effect on this species and therefore may not undermine the conservation objectives. (See Annex 1 Table 3.13, page 84). The distribution of River lamprey within the SACs is less certain.

Barriers and other in-stream/riparian beaver activities may impact sediment transport within rivers and streams, either directly or by influencing the hydrology of affected watercourses. This can negatively impact the replenishment of lamprey spawning areas, which like those required for Atlantic salmon are clean, well oxygenated, gravels.

SNH HRA advice conclude that there is the potential for beavers to have an adverse effect on site integrity of the SACs designated for lamprey through dam-building activities and other related activities. Mitigation to avoid these impacts is necessary. It is important to ensure that the passage of fish past any barrier is assured (this precautionary approach is currently needed due to the existing lack of understanding of the full details of any potential impacts on the SACs).

Mitigation

The efficacy of flow management devices for the downstream movement of juvenile lamprey, and the upstream migration of adult (particularly river and sea) lamprey is unknown. If flow management devices are not effective at facilitating the movement of lamprey species across in-stream barriers, then consideration must be given to alternative mitigation measures. These mitigation measures should be included in a Beaver Management Plan for the individual SACs, which should also set out in what circumstances there could be an adverse effect on site integrity, and a framework through which to implement any mitigation measures should they become necessary.

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.


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