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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.

Contents
Beavers in Scotland: consultation on the strategic environmental assessment
4.6 Beavers and Amphibians and Reptiles

4.6 Beavers and Amphibians and Reptiles

4.6.1 How beaver activity affects amphibians

Beaver activity results in the creation of ponds and slow-moving water, the changing of water tables and development of wetland habitat, all of which will generally benefit Scottish amphibians.

Scotland has six native amphibian species:

  • Frogs and toads (Anuran species) - common frog Rana temporaria, common toad Bufo bufo and natterjack toad Epidalia calamita
  • Newts and salamanders (Caudatan species) - smooth newt Lissotriton vulgaris, palmate newt Lessotriton helvetica and great crested newt Triturus vulgaris

The great crested newt and natterjack toad are European Protected Species [2] . All six species are dependent on water for breeding sites and all prefer, or are dependent on, standing water. The natterjack toad is the least likely to interact with beavers, as it is associated with coastal dune or saltmarsh habitats in Scotland, which are not expected to be potential beaver habitat.

4.6.1.1 Dam building

Dam-building on watercourses by beavers is the primary factor which will influence amphibians. Impoundment provides more standing water where flowing water was present before. The literature covering beavers' effects on amphibians is not large, although there are a number of published studies from North America. Whilst these support the idea that beaver impoundments are beneficial to amphibians, they largely concern guilds of species which are not fully analogous to the Scottish situation, for example stream-living salamanders.

One study examined the impact of beaver reintroduction on a guild of amphibians in the European central highlands, including four of the Scottish species. It found that beaver impoundments are important for all species, especially the common frog and palmate newt. Beaver ponds were compared with artificial ponds present before beaver reintroduction and it was concluded that artificial ponds acted as a surrogate for natural beaver ponds in their absence.

There is likely to be a benefit to amphibians, particularly anurans, where beaver dam-building changes the water table to induce wetland conditions. Newts, in the terrestrial phases of their annual cycle, favour damp rather than waterlogged habitats, such as leaf litter and friable dead wood. Hibernation sites are in damp habitats, and these would become unsuitable if they were waterlogged by beaver impoundments, although potential new sites may become available.

4.6.1.2 Fish within beaver impoundments

One negative aspect may be the presence of fish within these impoundments. Beaver ponds tend to be in-stream waterbodies rather than stand-alone ponds, isolated from fish colonisation. Great crested newts are particularly vulnerable to fish predation as their larvae are largely pelagic in habit, swimming in the water column to prey on species such as Daphnia and copepods. The larvae of the smaller newt species, and tadpoles of anurans, are more benthic, so are less vulnerable to, although not immune from, fish predation. Flooding by impounding or canal-building could also open up isolated ponds to fish invasion. Interactions between beaver dams and fish are further described in Annex 1 section 3.4.7.

One study reported evidence that great crested newts thrive in beaver ponds in continental Europe, although it also highlighted the need for fish-free conditions for great crested newt survival.

4.6.1.3 Impacts to riparian tree and aquatic plant cover

By reducing riparian tree cover, beaver activity can also raise the temperature of waterbodies by increasing insolation, a key factor in amphibian breeding success, particularly for great crested newts. Aquatic vegetation is important for cover for adult and larval amphibians and as egg-laying sites for newts. The effects of beaver presence on aquatic plants will vary between sites and are difficult to predict. Creation of ponds and wetland habitat is expected to increase the invertebrate biota overall ( Annex 1 section 3.4.6), and hence prey for all life stages of amphibians.

4.6.2 How beaver activity affects reptiles

There are three terrestrial reptile species native to Scotland:

  • Lizards - viviparous or common lizard Zootoca vivipara and slow worm Anguis fragilis
  • Snake - adder Vipera berus

There is also some evidence of populations of grass snake Natrix natrix in Scotland, although it is not known whether any of these have arisen from natural sources rather than from escaped captives or releases.

Effects on the three known native species are likely to be incidental. Viviparous lizards and adders can persist in wetland habitats but they are sub-optimal for them. Beaver foraging thins out woodland canopy, which could lead to greater insolation of the woodland floor and a potential increase in microhabitats with thermoregulatory benefits to reptiles, depending on the pattern of regrowth and ground flora regeneration.

The grass snake could benefit from beaver activity as it often hunts in water, and frogs can be a major prey component. They lay eggs in piles of rotting vegetation, notably compost heaps, where increased temperatures speed up the development of the young. Detritus within beaver lodge structures can provide such conditions.

A summary (see Table 4.6.1.) of the potential interactions between beavers amphibians and reptiles is presented below; where possible these have been attributed to a neutral, positive or negative effect.

Table 4.6.1: Summary of potential interactions between beavers and amphibians and reptiles.

Activity

Mechanism

Positive effects

Negative effects

Notes

Felling

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

  • Increased insolation of waterbodies will advance breeding times and accelerate maturation times in amphibians
  • Increased insolation will benefit reptiles through increased thermoregulatory opportunities

Felling

Change in riparian woodland: Amount/diversity of fallen dead wood on woodland floor

  • Increased fallen dead wood will provide additional foraging, resting and hibernation sites for amphibians and reptiles

Felling and constructions

Changes in amount/diversity of woody material in watercourses

  • May benefit amphibian larvae by providing shelter and foraging habitat diversity, and through increasing abundance/diversity of some invertebrate prey species

Feeding

Feeding on specific terrestrial herbaceous and aquatic plant species

  • Newts have plant species which they prefer to lay eggs on, so changes in plant composition may have some positive localised effects
  • Newts have preferred plant species on which to lay eggs, so changes in plant composition may have some negative localised effects

Dams/pond creation

Change from lotic to lentic habitat

  • Increase in lotic habitat will benefit breeding amphibians
  • Risk to great crested newt from fish predation where impoundments give access to fish predators

Dams/pond creation

Change in hydrological processes on riparian and downstream habitat

  • Increase in wetland habitat, and increasing habitat heterogeneity, will benefit amphibians overall
  • Some risk of waterlogging of hibernacula

Dams/pond creation

Changes in water quality downstream

Likely to be impacts on water quality of impoundments created downstream, which amphibians may use

Other constructions

Creation of lodges, burrows, canals, etc.

  • Lodge and dam structures will provide some benefit in providing shelter for amphibian larvae
  • Lodge and dam structures may provide shelter and breeding sites for grass snakes should they become established in Scotland
  • Canals may provide access for fish to great crested newt breeding ponds

Other

  • Beaver impoundments and structures may provide a haven for invasive non-native terrapin species

Indirect habitat creation/restoration initiatives as result of beaver presence

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

  • Presence of beavers may act as an incentive for greater investment, management and monitoring. This could include those related to the restoration and management of riparian woodland and wetland habitats

4.6.3 Distribution of amphibians and reptiles in the beaver policy area

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

4.6.3.1 Amphibians and reptiles of conservation importance

To determine whether the activity of beavers on amphibians and reptiles 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 4.6.2 below therefore identifies those amphibians and reptiles of conservation importance that utilise 'potential beaver core habitat' (as described in section 4.1 of this report) and are found within the beaver policy areas.

Turflundie Wood

Turflundie Wood SAC and SSSI is of conservation importance for its population of great crested newts Triturus cristatus, and for its assemblage of breeding amphibians, the richest in east Perth & Kinross. The site is predominantly an area of planted coniferous woodland and contains a number of natural and man-made pools which are used by breeding great crested newts, common frogs Rana temporaria, common toads Bufo bufo, palmate newts Lissotriton helveticus and smooth newts Lissotriton vulgaris. Despite this importance, the site does not overlap with potential core beaver habitat and so has been screened out of any further assessment.

There are no other designated sites in the beaver policy area for any amphibian or reptile species or assemblages that overlap with potential core beaver habitat.

Table 4.6.2: Summary of amphibians and reptiles of conservation importance within the policy area that overlap with potential beaver core habitat

Amphibians and reptiles species

Conservation importance

Great crested newt

EPS

4.6.4 Assessment of likely effects on amphibians and reptiles of conservation importance in the beaver policy area

The species identified in Table 4.6.2 above is 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. Where a species is afforded protection as a European Protected Species through the Habitats Regulation 1994, consideration is given as to the policy impact on the favourable conservation status of the population of the species in its natural range. Where mitigation or monitoring maybe appropriate, this has been identified in the narrative with further discussion relating to the management of beavers including mitigation and monitoring options is provided in section 5 and 7 of this report.

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.

Beaver opportunities

As mentioned above beaver activity has the potential to create many positive effects for a variety of native amphibian and reptile species. The presence of beavers may act as an incentive for greater investment, management and monitoring. This could include those related to the restoration and management of riparian woodland and wetland habitats.

4.6.4.1 Consideration of potential positive effects on amphibian species of conservation importance

Great Crested Newt

The great crested newt Triturus cristatus is the largest of the three British newt species with an adult length of 90 -170 mm. The adult male has a jagged crest along his back which decreases in size outside the breeding season. Both sexes are very dark in colour with a vivid orange belly patterned with irregular black spots. The skin is granular giving the species its alternative common name of warty newt.

The great crested newt spends the bulk of its life on land but is dependent on small to medium sized freshwater ponds to breed. Naturally a creature of rough grassland, scrub and woodland, the species has long been associated with lowland farmland but has also found a niche in former (and current) mineral workings and other 'brownfield' habitats. Terrestrial life is typically spent within 250 m of the breeding ponds but dispersal of up to 1000 m can occur.

They are nocturnal predators on invertebrates, spending daytime in damp refuges, for example, under stones and logs. Breeding takes place in ponds in spring to early summer, governed by temperature.

A number of positive and negative effects have been identified for great crested newts. Potential positive effects are anticipated to include:

  • Increased insolation of waterbodies will advance breeding times and accelerate maturation times in amphibians
  • Increased fallen dead wood will provide additional foraging, resting and hibernation sites for amphibians
  • May benefit amphibian larvae by providing shelter and foraging habitat diversity, and through increasing abundance/diversity of some invertebrate prey species
  • Newts have plant species which they prefer to lay eggs on, so changes in plant composition may have some positive localised effects
  • Increase in lotic habitat will benefit breeding amphibians
  • Increase in wetland habitat, and increasing habitat heterogeneity, will benefit amphibians overall
  • Lodge and dam structures will provide some benefit in providing shelter for amphibian adults and larvae

European Protected Species

Great crested newts are classed as European Protected Species, and are fully protected under The Habitats Regulations 1994 (as amended in Scotland).

In general, the spread of beavers would appear to be beneficial for amphibians in providing more pond habitat, especially in areas where the current stream gradients preclude standing water. Increased water tables may also create wet woodland or wetland habitat favourable to most amphibians.

While this assessment has identified the potential for some localised negative effects on great crested newt, which are discussed in section 4.6.4.2 below, it is anticipated that the potential impacts from the policy will not be detrimental to the maintenance of the population of the species (great crested newt) concerned at Favourable Conservation Status in their natural range.

4.6.4.2 Consideration of potential negative effects on amphibian species of conservation importance

A number of positive and negative effects have been identified for great crested newts. Potential negative effects are anticipated to include:

  • Newts have preferred plant species on which to lay eggs, so changes in plant composition may have some negative localised effects
  • Risk to great crested newt from fish predation where impoundments give access to fish predators
  • Some risk of waterlogging of hibernacula
  • Canals may provide access for fish to great crested newt breeding ponds

EPS Assessment

Great crested newts are classed as European Protected Species, and are fully protected under The Habitats Regulations 1994 (as amended in Scotland).

In general, the spread of beavers would appear to be beneficial for amphibians, a proviso might be that the continued presence of fish in beaver impoundments may not be ideal for great crested newts, although there is evidence from continental Europe that they do exploit beaver-created habitats. Despite the identified negative effects above, the interaction between great crested newt and beavers is likely to be broadly positive.

It is therefore anticipated that the potential impacts from the policy will not be detrimental to the maintenance of the population of the species (great crested newt) concerned at Favourable Conservation Status in their natural range.


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