European Site Conservation Objectives: Supplementary advice on conserving and restoring site features
River Ehen Special Area of Conservation (SAC) Site code: UK0030057
Credit: Diane O’Leary, West Cumbria Rivers Trust
Date of Publication: 7 March 2019
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About this document
This document provides Natural England’s supplementary advice about the European Site Conservation Objectives relating to River Ehen SAC.
This advice should therefore be read together with the SAC Conservation Objectives available here.
This advice replaces a draft version dated 24 January 2019 following the receipt of comments from the site’s stakeholders.
You should use the Conservation Objectives, this Supplementary Advice and any case-specific advice given by Natural England when developing, proposing or assessing an activity, plan or project that may affect this site.
This Supplementary Advice to the Conservation Objectives presents attributes which are ecological characteristics of the designated species and habitats within a site. The listed attributes are considered to be those that best describe the site’s ecological integrity and which, if safeguarded, will enable achievement of the Conservation Objectives. Each attribute has a target which is either quantified or qualitative depending on the available evidence. The target identifies as far as possible the desired state to be achieved for the attribute.
The tables provided below bring together the findings of the best available scientific evidence relating to the site’s qualifying features, which may be updated or supplemented in further publications from Natural England and other sources. The local evidence used in preparing this supplementary advice has been cited. The references to the national evidence used are available on request. Where evidence and references have not been indicated, Natural England has applied ecological knowledge and expert judgement. You may decide to use other additional sources of information.
In many cases, the attribute targets shown in the tables indicate whether the current objective is to ‘maintain’ or ‘restore’ the attribute. This is based on the best available information, including that gathered during monitoring of the feature’s current condition. As new information on feature condition becomes available, this will be added so that the advice remains up to date.
The targets given for each attribute do not represent thresholds to assess the significance of any given impact in Habitats Regulations Assessments. You will need to assess this on a case-by-case basis using the most current information available.
Some, but not all, of these attributes can also be used for regular monitoring of the actual condition of the designated features. The attributes selected for monitoring the features, and the standards used to assess their condition, are listed in separate monitoring documents, which will be available from Natural England.
These tables do not give advice about SSSI features or other legally protected species which may also be present within the European Site.
If you have any comments or queries about this Supplementary Advice document please contact your local Natural England adviser or email [email protected]
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About this site
European Site information
Name of European Site River Ehen Special Area of Conservation (SAC)
Location Cumbria
Site Map The designated boundary of this site can be viewed on the MAGIC website here.
Designation Date 1 April 2005
Qualifying Features See section below
Designation Area 24.39 ha
Designation Changes Not applicable
Feature Condition Status Details of the feature condition assessments made at this site can be found using Natural England’s Designated Sites System
Names of component River Ehen (Ennerdale Water to Keekle Confluence) SSSI Sites of Special Scientific Interest (SSSIs)
Relationship with other n/a European or International Site designations
Site background and geography
The River Ehen is an oligotrophic river in west Cumbria, spanning the Cumbria High Fells and West Cumbria Coastal Plain National Character Areas (see here). Over half of the upper portion of this Site is either within or on the boundary of the Lake District National Park.
The designated stretch of the river, between Ennerdale Water and the confluence with the River Keekle at Cleator Moor, meanders across a narrow floodplain with areas of riparian woodland and trees. Outside of the main urban areas of Ennerdale Bridge and Cleator Moor, the land is primarily agricultural, farmed mainly for sheep and cattle with associated hay/silage production for over-winter feed.
This Site supports England’s largest population of the freshwater pearl mussel (Margaritifera margaritifera) which is listed on the IUCN Red List of Protected Species as critically endangered in Europe. Salmon (Salmo salar), whilst designated in its own right as a feature of this Site, is an important host for the larvae (glochidia) of M. margaritifera. Glochidia attach to juvenile salmon in late summer and over-winter in the fish’s gills. Juvenile mussels drop-off of their fish host in spring where they burrow in to the river gravels, where they remain for several years. This buried stage within the life cycle is particularly susceptible to changes in river flow regime, siltation, excess algal biomass and eutrophication. The river has shown some juvenile mussel recruitment within the last 20 years, but not at levels capable of sustaining the population.
Above Ennerdale Bridge the catchment is largely composed of acidic rocks of the Borrowdale Series and Skiddaw Slates. Downstream from Ennerdale Bridge the river is slightly enriched by streams flowing from Limestones and Millstone Grits of the Carboniferous Series. This calcareous input has led to a
Page 3 of 36 heavier shelled morph of M. margaritifera downstream of this input which grows faster and with a thicker shell, but is shorter-lived.
Ennerdale Water is currently impounded by a weir which increases the capacity of Ennerdale Water for water storage for eventual abstraction for potable water supply. In 2012 it was determined that it could not be proven that these impoundment and abstraction activities were not having a detrimental effect on the integrity of the River Ehen SAC, and measures were put in place to find an alternative potable water supply. From mid-2012, compensation flows were increased to a minimum of 60 Ml/d (variable with lake level) in an attempt to improve flow conditions for mussels, and are now to a minimum of 80 Ml/day reducing to 60 Ml/day in line with Ennerdale lake level (Atkins & Gosselin, 2013). The current abstraction licence is due to be revoked in 2022 when a replacement water supply for West Cumbria is operational (the Thirlmere Transfer pipeline).
There is over-riding public interest to continue to provide public water supply until the replacement source is fully connected. In accordance with Article 6(4) of the Habitats Directive, compensatory measures need to be secured because it cannot be concluded that continued abstraction will not lead to an adverse effect on site integrity. Additionally, in 2014 the natural course of Ben Gill was restored to just downstream of the weir on Ennerdale Water, restoring coarse sediment supply back in to the river. This was also beneficial to both the freshwater pearl mussel and salmon because the top portion of the river between Ennerdale Water and Ennerdale Bridge was starved of coarse sediments, leading to degraded habitat for both species. The current Compensatory Measures package for the River Ehen SAC (funded by United Utilities and in collaboration with partners including Natural England and the Environment Agency) continues to deliver projects benefitting wildlife within the SAC and in the immediate surrounding area.
The SAC consists of two units: Unit 1 runs from the weir impounding Ennerdale to just below the confluence with Croasdale Beck. Unit 2 runs from this point just below the Croasdale Beck confluence to just before the confluence with the Keekle. Both units are currently Unfavourable Declining.
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About the qualifying features of the SAC
The following section gives you additional, site-specific information about this SAC’s qualifying features. These are the natural habitats and/or species for which this SAC has been designated.
Qualifying habitats:
Not applicable
Qualifying Species:
• S1029 Freshwater pearl mussel, Margaritifera margaritifera
The River Ehen supports the largest freshwater pearl mussel (Margaritifera margaritifera) population in England. The freshwater pearl mussel grows to around 150 mm in length and can live to be over 130 years old (Bauer, 1992; Skinner et al., 2003). M. margaritifera requires clean, fast flowing, highly oxygenated rivers and burrows into sand/gravel substrates, often between boulders and pebbles (Geist & Auerswald, 2007). The mussel requires a salmonid fish host for its larval (glochidial) stage; it is thought that the appropriate host fish in the Ehen is Atlantic salmon (Salmo salar). Glochidia are released into the water column by female mussels. If they encounter a juvenile salmonid, they attach to their gills, where they over-winter. Juvenile mussels drop-off of their fish host in spring and burrow in to the river gravels, where they remain for several years before emerging from the substrate to filter from the water column. As this species does not reach reproductive maturity until at least 12 years old and may live for over 130 years (Bauer 1992), population age-structure is vitally important when assessing viability. The presence of juveniles (a feature essential to the long-term sustainability of mussel populations) is a clear indicator of the structural and functional features of the habitat required for the survival and reproduction of the species. Exceptionally high densities (greater than 100 m2) are found at some locations, with population estimates for the entire river exceeding 500,000. The conservation importance of the site is further enhanced by the presence of juvenile pearl mussels, indicating recruitment in recent years. Worryingly, juvenile recruitment over the past decade has been poor indicating unsustainable pressures on the population which could lead to its extinction within a lifetime. In the River Ehen SAC, the population has declined because of factors such as habitat modification and associated impacts on natural flow regimes, pollution, nutrient enrichment, aggravated erosion of river banks and declining salmonid stocks. The freshwater pearl mussel is classified critically endangered across Europe (Cuttelod et al., 2011) and in the UK it is protected under Schedule 5 of the Wildlife and Countryside Act (1981).
• S1106 Atlantic salmon (Salmo salar)
The River Ehen holds a significant population of Atlantic salmon (Salmo salar), the environment agency classifies the population as “probably at risk” based on the 2017 assessment and (based on 2017 data) was predicted to remain in that status over the following five years. Recent estimates are that the salmon migration flow-range in the River Ehen is estimated to be between 90 – 390 Ml/d with peak migration occurring around 240 Ml/d. October through to the end of January is the key time for salmon migration in to the River Ehen SAC. Atlantic salmon are an anadromous species (i.e. adults migrate from the sea to breed in freshwater). Spawning takes place in shallow excavations called redds, found in shallow gravelly areas in clean rivers and streams where the water flows swiftly. After a period of 1-6 years the young salmon migrate downstream to the sea as ‘smolts’, where they spend between 1-3 years before returning to their native river to spawn. This behaviour has resulted in genetically distinct stock between rivers and even within individual rivers.
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Table 1: Supplementary Advice for Qualifying Features: S1029. Margaritifera margaritifera; Freshwater pearl mussel
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) Population Disturbance Restore the population size and Disturbance to Margaritifera margaritifera and their habitat, including killing Cauwelier et (of the from human distribution of Freshwater pearl or taking any part of the mussel is prohibited under the 1981 Wildlife and al.(2009) feature) activity mussel by avoiding significant Countryside Act. Engineering works that disturb river beds can be Geist & Kuehn disturbance to the feature and its disastrous for mussel populations, so every effort needs to be made to leave (2008) supporting habitats. them undisturbed. Changes to the river bed, banks and flow regime all have Karlsson et al. the potential to affect mussel beds through processes such as scouring, (2014) altered sediment delivery, provision of inadequate flows to all mussel life stages and effects on host fish availability. Even engineering works not close to mussel beds can have a detrimental effect on beds downstream where they significantly affect flows. As a minimum, existing areas should be safeguarded, whilst habitat lost through engineering works should be reinstated.
Other direct human activities can also disturb mussels, such as recreation (e.g. canoeing) and fishing (e.g. wading into river, maintenance of fishing pools). Local youths swimming in deeper pools near Cleator Moor is known to occur and has the potential to disturb mussels near these locations. Efforts should be made to highlight the international importance of freshwater mussels to individuals wishing to enter the river on a regular basis (e.g. fishermen). As a minimum, individuals entering the river should use a perspex-bottomed bucket (bathyscope) to check for mussels before stepping in to the river to avoid trampling. Disturbance of mussels or their habitat is prohibited unless carried out by a suitably trained and licenced person.
Mussel translocations both between and within rivers have been relatively unsuccessful, with mortalities of over 50% in the first three years having been recorded (Killeen & Moorkens, 2016). Translocation is not generally recommended as a conservation tool and there is some evidence to suggest that there may be host-specific interactions between mussel genetic conservation units and their salmonid hosts (Geist & Kuehn, 2008; Karlsson et al., 2014). Additionally, a genetic study carried out on English, Welsh and Scottish mussel populations (Cauwelier et al., 2009) recommended that each individual river (and sometimes individual populations within each river) should be treated as separate Conservation Units and not translocated out of river. Mussel translocations carry inherent risks such as stress on individual mussels from both the move and the potential that the
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) new site is not optimal compared to their original location, damage during translocation, creating river bed instability (because mussels help stabilise substrate) and the risks of mussels being washed downstream if not placed in their new location correctly. Mussel translocation should be regarded as a last-resort activity only if the population is under immediate threat of disturbance/mortality. Action should be concentrated on maintaining and enhancing all current populations.
There have been reported cases of off-roading within the Ehen catchment with vehicles crossing the river to access particular parcels of land. Vehicles should never enter the river Ehen at any time without prior consultation and subsequent consent of Natural England. Any vehicular access is likely to require a pearl mussel survey to ensure mussels are not present before works are undertaken.
Mussels close their valves in response to certain stimuli including sudden shading from above and hard or unexpected vibrations. Any individual wishing to carry out activities which include severe vibrations near the river should contact Natural England for advice. Population Population Restore the population of JNCC (2015); In 2012 the population was estimated to be ~510,000 individuals in the (of the abundance freshwater pearl mussel to a size Killeen & Moorkens upper Ehen with a conservative (lower) estimate of the habitat being able to feature) that is close to that expected (2012); support at least 600,000 individuals (Killeen & Moorkens, 2012). Mussels under un-impacted conditions Moorkens & Killeen are usually found aggregated in beds where substrate conditions prevail. throughout the site (taking into (2013); account natural habitat Recent mussel survey work between 2015 and 2017 has shown further Young et al. (2003); conditions and allowing for declines in the mussel population (Killeen & Moorkens, 2018b). Much of the Killeen & Moorkens natural fluctuations), whilst loss is likely to have occurred during the stress event of spring/summer (2018b) avoiding deterioration from its 2012, which caused a serious kill and ongoing stress and subsequent current level as indicated by the losses of mussels. latest mean peak count or equivalent. Margaritifera margaritifera is a long-lived species and so crude counts of individuals are not enough to show a thriving or failing population. Additionally, in large and dense mussel beds, carrying out thorough mussel surveys is very destructive and can damage the integrity of beds as well as individual mussels.
As a minimum the population should be maintained at the current estimated level (380,000 - 400,000; Killeen & Moorkens, 2018b), with a preference for population increase within the SAC. Page 7 of 36
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available)
The Ehen population is currently showing a lack of recruitment and is not sustainably recruiting. (Killeen & Moorkens, 2018a). Population Population Restore population viability by Juvenile recruitment is known to be the limiting stage in all English mussel Killeen & Moorkens (of the viability ensuring there is a diverse age populations. Juveniles should account for 20% of the population and at least (2012) feature) structure which reflects both some individuals should measure <30 mm if the population is to be classed Killeen & Moorkens active recruitment and longevity. as sustainably recruiting (JNCC, 2015; Young et al., 2003). In 2012, (2014) juveniles only accounted for 1 % of the population and most individuals were Killeen & Moorkens over 70 years old (Killeen & Moorkens, 2014). Killeen & Moorkens (2012) (2018b) have created estimated extinction curves for the Ehen population which Young et al. (2003) shows a worst case scenario of population extinction in less than 30 years (by around 2045) if sustainable recruitment is not achieved very soon. Additionally, the longer it takes to achieve significant recruitment success, the higher the risk of losing genetic diversity which will in turn threaten the population further as it becomes less capable of adapting to threats such as climate change.
There should be sufficient levels of juvenile recruitment to ensure that the population can withstand losses due to natural factors.
Killeen & Moorkens (2018b) assessed juvenile habitat in the Ehen and found that in the areas most able to support mussel populations, 29% of the habitat was classed as good juvenile habitat and of this, currently just over half (55%) of this was in good condition. One recommendation from this study was that it should be a conservation priority to improve the condition of the other 45%. Supporting Distribution of Restore the distribution and A contraction in the range, or geographic spread, of the feature across the habitat: supporting continuity of the Freshwater pearl site will reduce its overall area, the local diversity and variations in its extent and habitat mussel population and its structure and composition, and may undermine its resilience to adapt to distribution supporting habitat, including future environmental changes. Contraction may also reduce and break up where applicable its component the continuity of a habitat within a site and how well Margaritifera vegetation types and associated margaritifera is able to occupy and use habitat within the site. Fragmentation transitional vegetation types, of mussel beds can lead to larger ‘edge-effects’ which can further across the site destabilise mussel beds.
Margaritifera margaritifera is found throughout the SAC, aggregated in large beds at some locations. This species can form very dense beds which stabilise the underlying river substrate. Whilst river substrate is usually free to move, dense mussel beds can help consolidate substrate, protecting it
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) from scour during high flow events.
It is important that the extent of suitable habitat is maintained. An important feature of this is the provision of coarse sediment input from higher up in the catchment. The reconnection of Ben Gill is a recent (2014) reinstatement of a major coarse sediment source which will help improve mussel habitat, particularly at the head of the Ehen which has previously been particularly starved of coarse substrate. Developments which have the potential to alter coarse sediment input or increase fine sediment input to the river should be avoided. Supporting Extent of Restore the total extent of the In order to contribute towards the objective of achieving an overall Atkins & Gosselin habitat: supporting habitat(s) which support the favourable conservation status of the feature at a UK level, it is important to (2013) extent and habitat feature to total 24.39 ha restore the extent of supporting habitats and their range within this SAC. Quinlan (2014) distribution In this sense we define habitat as being the gravel in to which mussels bury because water flow and quality, which are equally important to mussels, are covered in different sections. Rivers are dynamic mosaic systems and as such there will never be 100 % habitat availability for mussels but areas which do not provide suitable habitat for mussels may be important for other species upon which mussels depend, like salmon.
In 2014 Ben Gill, an ephemeral stream which delivers coarse substrate in to the Ehen when it flows, was redirected to flow back in to top of the river Ehen. The mouth of Ben Gill was moved from the upper Ehen in to Ennerdale Water in 1971, cutting off coarse sediment supply to the river. Upon reconnection, this supply was reinstated and inputs of coarse material are obvious from the alluvial fan which has formed at the connection point. The most recent data looking at interstitial redox measurements (a proxy for interstitial dissolved oxygen) show that there are areas which provide suitable exchange with the water column, translating in to potentially good areas for juveniles. These areas are currently not as widespread as they could be and so the requirement is to further expand this area. Quinlan (2014) found high spatial and temporal variability in dissolved oxygen concentration in the Ehen indicating that some areas were impacted by poor interstitial/water column exchange (mirrored by the more recent redox measurements). Causes of poor water column/interstitial exchange include fine sediment (clay and silt) input. As such, any activity which increases fine sediment input should be avoided.
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) Supporting Biological Restore the free movement of Freedom of movement throughout the river system is critical to all life stages habitat: connectivity characteristic fish populations of fish host populations. Barriers to fish migration have cumulative effects on structure/ through the SAC the ability of individuals to reach spawning grounds and need to be function considered in combination.
Artificial barriers may have adverse effects on Margaritifera populations because they rely upon juvenile salmonids for part of their life cycle. Where there are adverse consequences, attempts should be made to restore fish migration, and to reverse other impacts such as impaired habitat connectivity, sediment transport, and invertebrate movement.
Salmonids require clean, stable, uncompacted gravels in which to cut redds. No activity should limit the supply of sediment within the designated area and gravel removal should only be undertaken under consultation with Natural England and the Environment Agency. In rivers containing Margaritifera populations no new artificial barriers should be constructed in the catchment. Supporting River habitat Ensure channel form and habitat There has been extensive physical modification of the river channel over the Alverez-Codesal & habitat: mosaic features are generally last two centuries. The river downstream of Ennerdale Lake to the River Sweeting (2015) structure/ characteristic of river type, and Keekle confluence (13.5km) has 37% of its length altered by mill-weirs, function have a predominantly unmodified leats, embankments and retaining walls. The Ehen below the confluence plan form. with the River Keekle to the sea (11.5km) has 62% of its length changed in a similar way (Alverez-Codesal & Sweeting 2015).
Historically, 17 mill weirs and 4 fishing weirs have existed on the river Ehen along its entire length (i.e. from Ennerdale Water to its mouth (Alverez- Codesal & Sweeting, 2015). These obstructions affect river flows, sediment transport, habitat availability and the ability of salmon to reach suitable spawning gravels near pearl mussel beds at the top of the river. Currently there are 6 weirs within the SAC, 3 of which are minor and don’t pose any threat to fish movement and 8 overall on the main stem of the Ehen, the other two being at Braystones and Egremont. Ennerdale Mill weir in Egremont was removed in summer 2018 which will make fish passage through this area significantly easier and also provide less opportunity for poaching.
Recent bank reinforcement has taken place at Slabs Corner (NY0455215453) to protect buried pipework (water for potable supply from Ennerdale Water) and seems to be causing localised issues with bank
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) erosion and river bed scouring downstream of this. There are a few areas where steep-sided cliffs are slumping quite badly (adjacent to Longmoor Common - NY0608915791 and upstream of this area), possibly due to changes to land and road drainage in the vicinity. Some parts of the main channel and its tributaries have been straightened historically but these extents are not significant.
The river channel is currently in a state of transition with some sections of the river retaining the form of the historic managed channel (with emphasis placed on limiting erosion and encouraging channel stability) which existed prior to the late twentieth century, and other sections showing active adjustment and an increase in the rate of geomorphological change (Jacobs 2010). The degree to which channel adjustment is impacting on the mussels will influence the long-term management strategy for the River Ehen.
Several improvements have been made to the catchment in recent years including removal of barriers to fish migration, reinstatement of coarse sediment delivery from Ben Gill, and establishment of a more suitable flow regime under the new compensation flow regime. These changes go some way to restoring natural process in the upper Ehen catchment so that the biotope mosaic is enhanced, and degraded areas have started to improve. Armouring of mussel and fish gravels upstream of Ennerdale Bridge is being addressed by the reintroduction of coarse sediment delivery from Ben Gill, but this will naturally take some time to re-establish this following over 40 years of coarse sediment starvation.
In December 2013 the Environment Agency confirmed the decision ‘to revoke the Ennerdale Water abstraction licence as soon as is reasonably practicable and to investigate options with regard to timing of weir removal and withdrawal of the compensation flow’. United Utilities have committed to investigating the feasibility of abstraction-related infrastructure removal following abstraction licence revocation, including the weir on Ennerdale Water along with associated infrastructure which may include smaller weirs just downstream. There is also the possibility of the Environment Agency’s gauging weir at Bleach Green being removed around the same time. Removal of these structures will help salmonids access spawning grounds much higher in the catchment as well as return the river to a naturally functioning system governed by natural processes.
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) Artificial physical habitat modifications should have no, or only minor, effect on physical habitat structure throughout the river, and there should be no increase in physical modifications from existing conditions.
Supporting Flow regime Restore the natural flow regime River flow affects a range of habitat factors of critical importance to IPENS (2014) habitat: of the river to ensure the area Margaritifera, including current velocity, water depth, wetted area, substrate Killeen & Moorkens structure/ occupied by mussels is not quality, dissolved oxygen levels and water temperature. The maintenance of (2018a) function reduced by loss of adult or both flushing flows and seasonal base flows, based on natural hydrological juvenile habitat through processes, is vital. The most appropriate way of ensuring adequate flow in inadequate flows. Margaritifera populations is to maintain a natural, abstraction-free regime in the sub-catchment influencing the population, and to manage the Maximum % reduction from daily surrounding catchment in a manner that does not affect the natural flow naturalised flows: * regime (e.g. by avoiding artificial drainage, coniferous or inappropriate Headwater; River; Large River afforestation, wetland removal, installation of weirs and dams). Similarly, if there are plans or projects being proposed in a catchment with Margaritifera,
Some improvements have been implemented in recent years including the reconnection of Ben Gill in 2014 which has restored coarse substrate delivery to the upper Ehen, increase in compensation flow since mid-2012 and removal of barriers such as Ennerdale Mill Weir in Egremont (2018). Reconnection of Ben Gill gives the upper Ehen a more natural hydrograph during high rainfall events when this ephemeral stream flows, as well as restoring vital coarse sediment delivery to the top of the system. Not only will this provide important habitat for juvenile mussels and fish, it will also help reduce armouring and over-deepening of the channel and increase flow heterogeneity in this section through the reinstatement of natural river features such as mid-channel gravel bars and point bars. The increase in compensation flow staged from 80 Ml/d reducing to 70 Ml/d and 60 Ml/d in line with Ennerdale Water lake level appears to be adequate to avoid stress
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) in adult mussels during summer high temperature conditions (Killeen & Moorkens, 2018a).
Available mussel habitat may be reduced where scouring occurs in areas of artificial high flows created by artificial structures such as revetments. Activities or developments which have the potential to restrict or change the flow pattern in the river are unlikely to be consented. Initial research is currently being carried out to inform decision-making on United Utilities infrastructure removal, including the main weir at Ennerdale Water. Investigative work on this is likely to begin in 2020. Supporting Negative In sustainable mussel habitat, Excessive cover of filamentous and epiphytic algae indicates nutrient Government habitat: indicators: maintain a low cover of enrichment, prolonged low flow and/or high summer water temperatures, Publications structure/ algal cover filamentous algae (either absent and may have an adverse effect on other biota and river habitats. If (Ireland) (2009) function or very sparse with <5% cover filamentous algae dies in situ and decomposes, this increases Biochemical during the season of maximum Oxygen Demand and decreases interstitial dissolved oxygen. This has a growth). particularly deleterious effect on juvenile mussels inhabiting the interstices and can lead to either direct mortality or indirect mortality through changes in behaviour (juveniles move to the substrate surface to exploit higher DO concentrations but have a higher risk of being washed away). Supporting Negative Ensure rooted macrophytes are Macrophytes are not typical of the fast-flowing, nutrient-poor streams Government habitat: indicators: either absent or rare (<5% cover) Margaritifera margaritifera is found in. Rare instances of macrophytes are Publications structure/ macrophytes within the mussel habitat in not necessarily cause for concern but growing macrophyte beds or anything (Ireland) (2009) function oligotrophic rivers. >5% cover in mussel habitat is not normal and may indicate persistence of sub-optimal flows and/or nutrient enrichment. It is important to note that this negative association refers only to Margaritifera margaritifera habitat. Rivers have a wide diversity of habitats; slower-flowing areas have naturally occurring macrophyte floras, so for water quality purposes only vascular plants in permanent mussel habitat should be assessed. Supporting Riparian zone Maintain the full extent of High riparian tree cover is beneficial for both salmonids and mussels in habitat: bank/riparian tree cover including terms of physical habitat provision from roots encroaching in to the channel, structure/ their root systems. combatting excessively high temperatures and a source of woody debris. function However, the extent of tree cover needs to be optimised to provide suitable conditions for the whole characteristic biological community. The riparian corridor within the Ehen catchment consists of a mixture of broadleaf tree cover with open areas of agricultural land. Conifer plantations are present at the top of the Ehen catchment but set back from the river and recent practice has been removal of conifer stands where possible and replacement with broadleaf trees.
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) The first few km downstream of the weir at Ennerdale Water are flanked by almost unbroken tree cover on both banks. This gives rise to patchier overhanging tree distribution downstream of Ennerdale Bridge. It is believed that the current tree extent is suitable to provide a mosaic of habitats in the Ehen for both salmonids and mussels.
Much of the riparian tree cover along the Ehen is not actively managed and often consists of stretches with a single line of even age-class trees. There is a requirement to manage/coppice trees in order to improve the riparian vegetation structure, open up overly shaded reaches and prevent the risk of trees falling in and damaging mussel beds.
There should be no reduction in riparian tree cover within the SAC and replacement of conifer stands with broadleaved woodland would be encouraged.
Inappropriate grazing of riparian areas can have a dramatic effect on mussel habitat through nutrient enrichment and soil inputs to the river. Where removal of livestock is not an option, wide buffer strips should be fenced next to the river so there is more chance of sediment/nutrient capture before it reaches the river and to allow natural riparian vegetation to recover. Supporting Sediment Restore a natural sediment load Natural levels of coarse sediment supply are critical to the maintenance of Quinlan et al. (2015) habitat: regime to supporting habitat, with high quality habitat for mussels and salmonids, maintaining the stability of structure/ concentrations of suspended the river channel and for creating and sustaining key habitat mosaics. Westcountry Rivers function solids not exceeding a guideline Excessive delivery of fine sediment, from the catchment or aggravated bank Ltd. (2015) annual mean of 10 mg L-1. erosion, may lead to a range of problems relating to surface siltation, the compaction, colmation or concretion of river beds and to the in-filling of Maintain oxygen exchange interstitial space. This affects oxygen supply and exchange between the between open water and substrate and the water column (Quinlan et al., 2015), as well as the ability interstitial water, indicated by no of juvenile mussels to burrow. Infiltration by fine sediments is one of the more than 20% loss in redox main causes of decline in juvenile recruitment for pearl mussel populations. potential between open water and interstitial water at 5 cm Margaritifera are vulnerable to the effects of unnaturally elevated levels of depth.* suspended solids. Elevated suspended solids can elicit clamming for extended periods of time which interrupts normal feeding and respiratory activity. This may lead to stress and mortality, particularly in juveniles. In unimpacted rivers, suspended solids should not be detectable. Low intensity inputs of particles resulting in short-term spikes may occur during snowmelt or heavy rain but suspended solids should be consistently <10 mg L-1.
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) Higher incidences are indicative of aggravated fine sediment input and this should be investigated. One of the main sources of increased turbidity in pearl mussel catchments is drained agricultural land delivering suspended solids to the river (Westcountry River Ltd., 2015).
Supporting Soils, Restore the properties of the Land use in the catchment is dominated by cattle/sheep farming and habitat: substrate and underlying soil types, including associated activities. This brings with it the potential for increased soil and structure/ nutrient structure, bulk density, total nutrient input to the river where best practices are not followed. The role of function cycling carbon, pH, soil nutrient status organic detritus in mussel diets/ecology is not fully understood but the and fungal: bacterial ratio, within current land use will almost certainly have led to a breakdown of natural soil typical values for the supporting processes affecting the structure, pH soil nutrient status and fungal: habitat bacterial ratio. Whilst this doesn’t have a direct impact on Margaritifera increased nutrient and silt inputs are known to have a direct detrimental impact on mussels, particularly juveniles. Any activity which has the potential to increase nutrient/silt input to the river should be avoided. Additional research is required as to whether organic detritus from functioning wetlands is important for juvenile mussels to inform management practices going forward. Supporting Invasive non- Ensure invasive non-native Alien species of plants, both freshwater macrophytes and riparian species, habitat: native species species which pose a threat to can change the nature of the substrate and riparian habitats, respectively. structure/ the feature are either absent or Spread of aquatic macrophytes, whether native or alien, increases fine function being contained at a level which sediment accumulation within gravels and is a negative indicator within does not significantly affect the suitable habitat for pearl mussels. The spread of riparian alien species such feature as Japanese knotweed (Fallopia japonica) or Himalayan balsam (Impatiens glandulifera) reduces riparian species richness and can change the nature of river banks. Japanese knotweed and Himalayan balsam stands can out- compete native grasses, causing large areas of bare earth. When they die back, this leaves large areas of exposed soil on the banks which are vulnerable to erosion. Additionally, bare earth does not provide any resistance to flows when they rise out of the banks, increasing flow velocity compared to vegetated areas. Non-native plants that spread widely and colonize gravel banks can render them too stable compared with natural rates of gravel movement. Additional species including monkey flower (Mimulus guttatus) and skunk cabbage (Lysichiton americanus) can tolerate wet habitats and so bind mid-channel or point bars. Conversely, non-native species can prevent native woodland species from colonizing, causing river banks to become more susceptible to erosion in flood conditions. In addition, changes in bank vegetation may have effects on detritus and food
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) composition for juvenile mussels.
The spread of alien macrophytes and riparian plants should be recorded when monitoring Margaritifera populations. Any conservation plan or development project should ensure that non-native macrophytes and riparian species are eradicated if possible, and as a minimum not aided in their spread or in their ability to reach beds of mussels. Any eradication should be done with care as removal of these species can also lead to instability and bank erosion, which can lead to sedimentation.
Supporting Water quality: Ensure pH levels are Freshwater pearl mussels normally live in naturally slightly acid to neutral Maberly et al. (2016) habitat: acidification maintained/restored within the waters, at pH between 6.2 and 7.3. The natural pH range for an individual structure/ range 6.2 - 7.3 (must be at a river may vary, so it is important that this is determined. It is almost function natural level for the river). impossible to truly know what the historic pH of the system was in its reference state. Environment Agency pH spot samples commence at some sites in 1976 (Bowness Knott (Ennerdale), Bleach Green, Ennerdale Bridge, Wath Brow, Ennerdale WTW and just upstream of the Keekle confluence). pH was also logged every 15 minutes at Bleach Green from 30 June 2010 – 23 July 2012. From historic spot samples it appears that there is a slight overall increase in pH at every site over the time series (1976 – 2018) from approximately high 6’s – low 7’s, rising to mid – high 7’s more recently.
There is also an increase in pH spikes over 8 in the last decade also. These data are consistent with long term data from the CEH Lakes Tour which includes Ennerdale Water suggesting that a decrease in sulphate pollution from acid rain is increasing alkalinity and pH (Maberly et al., 2016). Without knowing the reference pH of the system it is not known if this rise in pH is cause for concern. The data logged every 15 minutes between 2010 – 2012 at Bleach Green are slightly different with fewer peaks above pH 8 observed and a more stable pH profile around the upper 6’s – lower 7’s. It should be noted however that the river Ehen has very low conductivity and so obtaining reliable pH readings is difficult without specialist sensors (which were not used for EA data collection). The data should therefore be treated with caution.
Both unnatural acidification and unnatural calcareous flushes are damaging to mussel populations so any activity which causes high fluctuations in pH should be avoided.
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) Supporting Water quality: Maintain Environmental Quality Available data (2007 – 2011) shows that the macroinvertebrate EQR (both habitat: macroinverte Index (EQI) /Environmental ASPT and NTAXA) are classified as High. Any activities within the structure/ brates Quality Ratios (EQRs) at a high catchment should not threaten this High status classification. function ecological status Supporting Water quality: Maintain levels of Soluble All steps necessary should be taken to avoid nutrient input to the river. Moorkens (2006) -1 habitat: nutrients Reactive Phosphorus: ≤ 5µg L Several studies have suggested suitable phosphorus concentrations based JNCC (2015) structure/ SRP annual mean) depending on upon juvenile recruitment within these catchments (British Standards Westcountry Rivers function reach (ECS) type * Institution, 2017 and references therein) and the Common Standard Ltd. (2015) Monitoring Guidance (JNCC, 2015) states that where annual mean soluble reactive phosphorus levels are <5 µg L-1, the limit should be 5 µg L-1. This British Standards appears to be the case in the Ehen and so this limit should be adhered to. Institution (2017) This concentration coupled with the absence of excess filamentous algae growth should indicate a low-nutrient system and one which should be capable of supporting Margaritifera margaritifera.
Specific sources/potential sources of phosphorus to the river Ehen include wastewater treatment, septic tanks (both residential and commercial), agriculture and forestry. Westcountry Rivers Ltd. (2015) found that the main source of SRP at a catchment scale was from sewage treatment works with agriculture being another major contributor. Within the current Margaritifera population area, the sewerage pressure is from numerous on-site waste water treatment/septic tank pressures rather than from a concentrated sewerage treatment works. Supporting Water quality: Restore water quality by limiting Organic pollution affects Margaritifera in a number of ways, including direct habitat: organic the concentrations of organic toxicity (from ammonia and nitrite), reduced dissolved oxygen levels (from structure/ pollution pollutants to the following levels; microbial breakdown of organic material), and nutrient enrichment. function Reducing organic pollution levels reduces toxic effects but unmasks Dissolved Oxygen DO (% enrichment effects. Controlling the continuous input of low levels of organic saturation): >85 %; material is critical to controlling the enrichment effect. Mean BOD (mg L-1): <1.0 ; Ammoniacal N <0.01 mg L-1 Dissolved oxygen concentrations within the interstices are critical for juvenile mussels. Several monitoring techniques are available such as using DO data loggers (Quinlan et al., 2014) and using the difference in redox potential between the interstitial and open-water (Geist & Auerswald, 2007) as a proxy for interstitial DO levels. No DO limit/target has been proposed for juveniles within the interstices but Quinlan et al. (2014) highlight the need for consistently high DO concentrations for buried juveniles, as even short- term decreases can lead to mortalities or changes in behaviour leading to mortality.
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available)
-1 Elevated BOD5 (>1.4 mg L ) has been linked with poor juvenile survival in Central Europe (British Standards Institution, 2017; JNCC, 2015) whilst rivers with reproducing populations in the UK, Ireland and Spain consistently -1 have BOD5 levels <1.0 mg L .
The CEN standard providing water quality guidance for the freshwater pearl mussel (British Standards Institution, 2017) reports that recruiting rivers in Ireland have ammoniacal N levels never exceeding the detection limit (0.01 mg L-1). Supporting Water quality: Ensure there is no exceedance Very little is known about the effects of different contaminants and heavy Wang et al. (2007) habitat: other of the relevant Environmental metals on freshwater mussels. In the USA juvenile freshwater mussels have structure/ pollutants Quality Standards (or Predicted been found to be more sensitive to a wide range of pollutants than function No Effect Concentrations) for organisms traditionally used in toxicology studies (Wang et al., 2007). Owing potentially toxic contaminants to the high sensitivity of Margaritifera margaritifera, WFD limits for toxic such as heavy metals. substances should be strictly adhered to. In general, the precautionary principle should apply where there is no information on the effects of potential pollutants, owing to the sensitivity of Margaritifera margaritifera. It is known that metals such as Copper, Cadmium, Zinc and Nickel, are toxic to many mussels. Supporting Woody debris Maintain an abundance of large Trees are an important part of riparian habitats and in Margaritifera rivers habitat: woody debris within the channel. both living trees and dead wood help to create variation in riverine habitat structure/ and provide shelter and, indirectly, food for their salmonid hosts. In general, function therefore, woody debris should not be removed from the water.
It is important that a fallen tree does not constitute a severe impact on suitable Margaritifera habitat. Where a tree falls directly onto a mussel bed it can cause damage by impeding water flow and causing river-bed changes through scouring or weir effects. In these situations, it may be better to remove the tree partly or to remove a tree in danger of falling into the river. Supporting Adaptation Restore the feature's ability, and The overall vulnerability of this SAC to climate change has been assessed NATURAL processes and resilience that of its supporting habitat, to by Natural England (2015) as being moderate, taking into account the ENGLAND, 2015. (on which the adapt or evolve to wider sensitivity, fragmentation, topography and management of its Climate Change feature and/or environmental change, either habitats/supporting habitats. This means that this site is considered to be Theme Plan and its supporting within or external to the site vulnerable overall but moderately so. This means that some adaptation supporting National habitat relies) action for specific issues may be required, such as reducing habitat Biodiversity Climate fragmentation, creating more habitat to buffer the site or expand the habitat Change Vulnerability into more varied landscapes and addressing particular management and assessments condition issues. Individual species may be more or less vulnerable than (‘NBCCVAs’) for Page 18 of 36
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) their habitat itself. In many cases, change will be inevitable so appropriate SACs and SPAs in monitoring would be advisable. England [Available at Freshwater mussels are sedentary organisms and the only method of http://publications.na naturally increasing their distribution range is when juveniles excyst from turalengland.org.uk/ their host in to new, suitable areas of substrate. Climate change poses a publication/4954594 real threat to mussel populations through issues such as rising water 591375360 ]. temperatures and increasing numbers of flood/drought events which could put the Ehen mussel population under further pressure.
The most effective way to prepare the population for a changing environment is to have a functioning, sustainably recruiting population which should be more resilient to change. Additionally, removing pressures from inappropriate land use and restoring catchments so they have functioning natural processes will make the catchment more resilient to changing climates and minimise pressures on pearl mussels. Afforestation of broadleaved woodland along river corridors may help buffer aquatic species from rising water temperatures through shading. However, evapotranspiration levels of trees during drought conditions can have a deleterious effect on the hydrological cycle which in turn exacerbates low water velocities. Therefore, this strategy will not be appropriate at all locations. Supporting Air quality Maintain or, where necessary, The Air Pollution Information System does not provide estimates of critical More information processes restore concentrations and loads or level values for any of the designated features of the site. The about site-relevant (on which the deposition of air pollutants to at catchment does not support significant heavy industry and air pollution is not Critical Loads and feature and/or or below the site-relevant Critical thought to be an issue currently. The majority of nitrogen inputs to the river Levels for this SAC its supporting Load or Level values given for come from agriculture. is available by using habitat relies) this feature of the site on the Air the ‘search by site’ Pollution Information System Any developments which may increase air pollution significantly would need tool on the Air (www.apis.ac.uk). to be carefully considered by Natural England and any developments which Pollution Information have the potential to significantly increase levels of dust which may settle in System to the river should be discouraged. Mussels are sensitive to suspended (www.apis.ac.uk). solids so any activity increasing suspended solids in the Ehen is likely to be refused consent. Supporting Conservation Restore the management Active and ongoing conservation management is needed to protect, IPENS (2014) processes measures measures (either within and/or maintain or restore this feature at this site. Further details about the English Nature (on which the outside the site boundary as necessary conservation measures for this site can be provided by (2004), Views about feature and/or appropriate) which are necessary contacting Natural England. This information will typically be found within, management of its supporting to restore the structure, functions where applicable, supporting documents such as Natura 2000 Site River Eden SSSI Page 19 of 36
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) habitat relies) and supporting processes Improvement Plan, site management strategies or plans, the Views about associated with the feature Management Statement for the underpinning SSSI and/or management and/or its supporting habitats. agreements. Supporting Control of Restore appropriate levels of The majority of land in the Ehen catchment is grazed farm land, primarily processes livestock livestock grazing to riparian with sheep and cows. Over-grazing of riparian areas has a dramatic effect (on which the grazing areas of the SAC on Margaritifera margaritifera and salmonid habitat. Over-grazing on drained feature and/or activity land leads to rapid run-off routes during rainfall which can introduce its supporting sediment and contaminants (fertiliser, pesticides & herbicides) in to the habitat relies) water course. Ideally, grazing levels should be managed at low levels across whole riparian fields with a preference for holistic land management and no/minimal nutrient input. Where this is not feasible, set-back fencing creating wide buffer strips between grazed land and the river channel may be established. Margaritifera is present along the entire SAC reach and so cattle access to the river should be avoided to protect against trampling and bank poaching. Use of solar-powered pumps and cattle-activated drinking points are good alternatives to allowing cattle access the river for water. Supporting Fish host Restore the abundance of The long-term survival of Margaritifera depends ultimately upon host Butterill (2014, 2015) processes population juvenile salmonids at the level availability. There is concern that significant changes in salmon and sea Geist et al. (2006) (on which the expected for the river type under trout stocks may threaten pearl mussel populations. Densities of fish should O’Leary (2015, feature and/or conditions of high physical and be those that are typical for the natural trophic status of each individual river. 2016, 2017a) its supporting chemical quality. Increased fish biomass and number of species can be indicative of nutrient Sweeting & Miles habitat relies) enrichment bringing increased competition and a subsequent decrease in (2010) juvenile mussel survival.
The Ehen is an oligotrophic system and as such, fish biomass should be lower than in non-oligotrophic systems. Where there are specific problems affecting fish populations, such as barriers to migration, high summer temperatures or acidification, low host numbers can be a limiting factor for Margaritifera margaritifera recruitment. The river Ehen is affected by several weirs which affect salmonid migration. In 2018, Ennerdale Mill Weir at Egremont, was removed and the river bed restored, significantly improving fish passage beyond this reach.
Suitable hosts in the UK are native salmonid fish, such as Atlantic salmon (Salmo salar), brown/sea trout (Salmo trutta) and possibly even Arctic charr (Salvelinus alpinus) where they are native. From previous electrofishing surveys (Butterill, 2014, 2015; O’Leary, 2015, 2016, 2017a) and studies in captivity (Sweeting & Miles, 2010), salmon appears to be the preferred host in the Ehen, although trout appears to be an occasional host. Geist et al.
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) (2006) and references therein state acceptable trout densities for mussel recruitment are between 0.1 – 0.2 m-2. These densities should be treated with caution as they are derived from non-UK catchments and each catchment is different. It does however provide a useful estimate of the range of salmon densities which should be observed in the Ehen. In addition, the 2017 CEN Standard (British Standards Institution, 2017) provides a checklist of monitoring recommended on fish hosts in rivers with Margaritifera which should be adhered to. Supporting Fisheries - Maintain sustainable levels of See notes above for Fisheries - introduction of fish species attribute processes exploitation fish exploitation (e.g. netting or (on which the angling) which do not interfere feature and/or with the ability of the river to its supporting support self-sustaining habitat relies) populations of characteristic species, including multi-sea winter fish and seasonal components of the adult run.
Supporting Fisheries - Ensure fish The fish community associated with Margaritifera rivers is important processes introduction stocking/introductions do not because the microscopic larvae (glochidia) attach to the gills of salmonids (on which the of fish interfere with the ability of the before detaching and becoming a juvenile mussel. This process helps feature and/or species river to support self-sustaining maintain and extend population distribution. Artificial introduction of fish its supporting populations of freshwater pearl carries various ecological risks, including competition between stocked and habitat relies) mussel native individuals, disease introduction and genetic alterations to the population. Rainbow trout and brook trout may not be compatible mussel hosts and this may decrease the success of glochidia at this life-cycle stage.
Proposals to artificially stock fish in catchments with Margaritifera should be subject to an appropriate risk assessment, and if required should only be with the local native strain that is known to support the pearl mussels of that population. In general, supporting natural recovery of fish stocks is a better policy than artificial stocking, even with native salmonids. The overall aim is to provide conditions in the river that support a healthy, natural and self- sustaining fish community, achieved through habitat protection/restoration and managed exploitation as necessary. Supporting Integrity of Refer to targets set for salmonids Habitats beyond the site boundary upon which characteristic biological O’Leary (2017b, processes off-site communities of the site depend should be maintained in a state that does 2018) (on which the habitats not impair the full expression of the characteristic biota within the site. feature and/or Page 21 of 36
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) its supporting Salmonid host populations within the SAC are dependent on the integrity of habitat relies) sections of river channel, riparian areas, and transitional and marine waters that lie outside of the site boundary. Headwater areas and tributaries may not fall within the site boundary, yet salmonids may use these areas for spawning and juvenile development and are critical for sustaining the mussel population within the site. Electrofishing carried out in 2017/2018 has found four major tributaries (Mere, Hole, Red and Croasdale becks) are capable of supporting fair populations of brown trout but not many salmon (O’Leary, 2017b, 2018). The lack of salmon is particularly concerning as there is good evidence it is the preferred host fish species.
Fully-developed riparian zones free from invasive species are essential for Margaritifera margaritifera habitat, yet part of this zone may lie outside of the site boundary, particularly if the river channel is operating under natural processes and moves laterally over time within the floodplain. If there are bare patches in the riparian strip or fertiliser/pesticide application, there is potential for enrichment/contamination and silt input to the Ehen when the river does inundate the floodplain during high flows, This should be taken in to consideration when carrying out any activity within the floodplain. Supporting Water Restore water quality and Water quantity and quality are the two most important parameters for pearl Moorkens & Killeen processes quantity/ quantity to a standard which mussels. Water quality is dealt with in more detail below and so is not (2014); Killeen & (on which the quality provides the necessary mentioned here (see water quality: nutrients, organic pollution, acidification, Moorkens (2018a) feature and/or conditions to support the other contaminants sections). its supporting freshwater pearl mussel feature. habitat relies) Water quantity is key. Mussels require substrate which is stable but not compacted in which to bury. Interstitial water exchange should be sufficient to deliver enough food and oxygen to juvenile mussels (living at 5-10 cm depth). Traditional flow measurements taken at 0.6 metres of water column depth does not relate to near-siphon level (typically <3cm above substrate) and also tells us nothing about interstitial water flows. Moorkens & Killeen (2014) found that near-bed velocities remain high in recruiting freshwater mussel populations indicating that the species is adapted to stable substrate with low silt infiltration kept clean with high water velocities rather than silt infiltration followed by flushing flows. Flow in the Ehen is currently altered due to the impoundment of Ennerdale Water. The compensation flow regime in the Ehen is specified on the Ennerdale Weir impoundment licence and is staged from 80 Ml/d, reducing to 70 Ml/d to 60 Ml/d minimum depending on lake level. Stress testing on mussels in the Ehen in 2018 concluded that this compensation flow provided adequate provision for
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) mussels to maintain them in an unstressed state during 2018 summer high temperatures and an extended period of low rainfall (Killeen & Moorkens, 2018a).
As part of the Compensatory Measures package agreed between United Utilities, Natural England and the Environment Agency, initial research is currently under way to model how the system may function if the weir at Ennerdale Water was removed. These studies will be further developed as part of environmental assessments required in support of any future applications for consents to remove abstraction related infrastructure at Ennerdale following abstraction licence revocation. It is important that the new channel exiting Ennerdale Water is able to provide sufficient flows to the Ehen under drought conditions. Version Control Advice last updated: Feb 28th 2019. Changes and additional text to the 2012 population abundance target. Response to concerns raised by stakeholder regarding riparian tree cover and physical modification (issues validated by Natural England area team and specialist) Variations from national feature-framework of integrity-guidance: Water quality: Organic pollution attribute targets written within this section mirror the Common Standards Monitoring guidance or the CEN standard (British Standards Institution, 2017) where CSM guidance was not provided. Water quality requirements for pearl mussels exceed those of Water Framework Directive - High status. The 0.01 mg/L for ammoniacal-N target has been in place for c.10 years
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Table 2: Supplementary Advice for Qualifying Features: S1106. Salmo salar; Atlantic salmon
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) Population Adult run size Restore the Atlantic Salmon Impacts on physical, chemical or hydrological integrity, or from non-native (of the population to that expected under species, or from exploitation in freshwater or marine and coastal waters, may feature) un-impacted conditions, allowing suppress adult run size. Stocking may also artificially augment adult run size, for natural fluctuations. and may mask environmental problems or generate impacts on naturally spawned individuals. The Conservation Limit should be based on the adult run size required to fully utilise all parts of the catchment that would be suitable for spawning and juvenile development under unimpacted conditions.
Population Juvenile Restore juvenile densities at Impacts on physical, chemical or hydrological integrity, or from non-native Environment (of the densities those expected under un- species, or from exploitation of spawning adults in freshwater or marine and Agency (2016) feature) impacted conditions throughout coastal waters, may suppress juvenile densities. There is a general Environment the site, taking into account agreement locally that the number of salmon in the river has decreased within Agency (2018) natural habitat conditions and living memory. However, this does not mean that the current salmon allowing for natural fluctuations population level is lower than would be expected in an oligotrophic system. More research needs to be done to investigate what the expected fish biomass in the Ehen should be and how this relates to current levels.
There is no fish gauge on the Ehen so salmon returns cannot be analysed in great detail. Rod licence data however provides some basic information. Salmon rod catches between 2007 – 2017 show that between 2014 – 2017 there may have been a slight decline in the number of salmon caught (Environment Agency, 2018). There is no way of knowing however if this is a natural fluctuation in salmon numbers or if the catch per unit effort is different between these timescales. The salmon population in the river Ehen is thought to be “Probably at Risk” currently and is expected to retain this classification in 2021 (Environment Agency, 2016). Population Spawning Restore the distribution of After a year or more at sea, adult salmon return from their feeding grounds (of the distribution spawning to reflect un-impacted back to their river. Once it is time for them to spawn they will migrate feature) conditions through the site, and upstream to the areas of the SAC where they were born to spawn avoid reductions in existing themselves. These spawning areas may be in small tributaries of river levels. systems where there is clean gravel and a good flow of fresh clean water. Maintaining these spawning areas is critical to the successful reproduction and long-term viability of this feature. Barriers to fish migration affect the ability of returning fish from moving up the river and smolts from moving down. These weirs also affect the habitat around them, causing ponding upstream and scour downstream therefore decreasing the total area of Page 24 of 36
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) potential spawning habitat for salmon. Supporting Distribution of Restore the distribution and A contraction in the range, or geographic spread, of the feature (and its habitat: supporting continuity of the feature and its component vegetation) across the site will reduce its overall area, the local extent and habitat supporting habitat diversity and variations in its structure and composition, and may undermine distribution its resilience to adapt to future environmental changes. Contraction may also reduce and break up the continuity of a habitat within a site and how well the species feature is able to occupy and use habitat within the site. Such fragmentation may have a greater amount of open edge habitat which will differ in the amount of light, temperature, wind, and even noise that it receives compared to its interior. These conditions may not be suitable for this feature and this may affect its viability. Supporting Extent of Restore the extent of the habitat There is the feeling that salmon numbers have declined in recent memory but McCubbing (1997) habitat: supporting which support the feature it is difficult to say whether this is because of a general improvement (i.e. Environment extent and habitat decline) in nutrient enrichment in recent years leading to a subsequent Agency (2018) distribution reduction in fish biomass or whether salmon stocks are truly lower than they were historically. The river Ehen does not have a fish counter and so less accurate methods of measuring salmon numbers must be used, including data from rod licences or red counts. Data from licence returns show a decrease in salmon rod catch from 680 - 996 per year in the early 1960’s to lows of <100 per year during the 1970 – 1980’s (McCubbing, 1997). This improved somewhat in the late 1980’s and early 1990’s to approximately 200 per year (McCubbing, 1997) and more recent numbers indicate a slight improvement on these numbers between 2007 – 2013 but a decline again to 115 in 2016 and 200 in 2017 (Environment Agency, 2018). There is no way of knowing however if these numbers show a true decline in salmon numbers because we cannot assess the catch per unit effort.
There are identified areas within the SAC where habitat is not optimal and not likely to be suitable for salmon spawning or to support juvenile fish. This includes areas of the river upstream of Ennerdale Bridge, which may be armoured due to dirth of coarse sediment supply (until Ben Gill was reconnected in 2014). Several major weirs on the Ehen still exist which affect fish movement and habitat availability. Supporting Biological Restore free movement of Freedom of movement throughout the river system is critical to all life stages habitat: connectivity Atlantic Salmon through the of salmon. Barriers to fish migration have cumulative effects on the ability of structure/ SAC. individuals to reach spawning grounds and need to be considered in function combination.
Removal of barriers to fish migration are to be encouraged, such as the Page 25 of 36
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) removal of Ennerdale Mill Weir at Egremont in summer 2018. This not only helps upstream salmonid migration but connects previously separated areas of the lower Ehen to improve fry and parr movement within this reach, as well as improving movement of young salmon out to sea. Removal of these significant barriers also reduces the opportunity for illegal poaching of fish stocks and improves the hydrology of the river in this reach and further downstream. This in turn has the potential to improve and increase the distribution of suitable spawning habitat and habitat for young fish.
Remaining significant weirs and blocks to fish migration are the main dam between Ennerdale Water and the river Ehen, Hartley’s weir and the EA gauging weir at Bleach Green. There is a fish pass on the weir at Ennerdale Water which was installed in the 1990’s. It is accepted that the passage of fish past this weir is not as effective as it could be and several attempts have been made to improve the design in recent years. United Utilities have made some modifications to the fish pass to improve passage in late 2018. In line with the river Ehen Compensatory Measures package negotiated by United Utilities in partnership with the Environment Agency and Natural England, initial research is being carried out focussing on the removal of abstraction-related infrastructure at the top of the river Ehen in order to return the system to a hydrologically naturally functioning system. These studies will be further developed as part of environmental assessments required in support of any future applications for consents to remove abstraction related infrastructure at Ennerdale following abstraction licence revocation.
Other weirs below the SAC which may affect fish passage are Hartley’s weir in Egremont and the gauging weir at Braystones. Fish are able to pass these weirs in the right flows but they do represent blocks which will slow fish passage. Ennerdale Mill weir in Egremont was removed in 2018 and the river returned to a riffle habitat. Supporting Biotope Restore the extent and pattern of Within the river, a characteristic habitat mosaic shaped by natural processes habitat: mosaic in-channel and riparian biotopes provides the diversity of water depths, current velocities and substrate types structure/ (habitats) to that characteristic of necessary to fulfil the spawning, juvenile, adult and migratory requirements of function natural fluvial processes. salmon as well as other characteristic species. Some river sections will be naturally sub-optimal for some salmon life stages, and this is just a characteristic of the river. The species requires adult holding areas (generally pools of at least 150 cm depth, with cover from features such as undercut banks, vegetation, submerged objects and surface turbulence), spawning habitat (stable, clean gravel/pebble-dominated substrate without an armoured
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) layer and with <10% fines in the top 30cm, and with 15-75cm of overlying water), nursery habitat (for fry, water of <20 cm deep and a gravel/pebble/cobble substrate; for parr, water 20-40 cm deep and similar substrate). Close juxta position of biotopes is needed to allow easy movement of individuals between suitable areas of the channel under different flow conditions and with age.
Several improvements have been made to the catchment in recent years including removal of barriers to fish migration (and return of this area to riffle habitat), reinstatement of coarse sediment delivery from Ben Gill, and establishment of a more suitable flow regime under the new compensation flow regime. These changes go some way to restoring natural process in the catchment so that the biotope mosaic is enhanced, and degraded areas have started to improve. Armouring of mussel and fish gravels upstream of Ennerdale Bridge is being addressed by the reintroduction of coarse sediment delivery from Ben Gill, but this will naturally take some time to re-establish this following over 40 years of coarse sediment starvation. Challenges are still present, one of the major ones being upstream migration of salmon past Ennerdale Water but strategies are being implemented to investigate and address these challenges in the near future. It is noted that United Utilities have implemented some improvement measures to the existing fish pass at Ennerdale Water weir in 2018.
Retention of large woody debris is a balancing act with considerations for the mussel population but proper pinning of trees/large boughs is occurring which will provide refuges for young salmonids. The continued presence of in-river roots from trees also provides protection to young salmonids so care should be taken to maintain this. Supporting Flow regime Restore the natural flow regime The natural flow regime is critical to all aspects of the salmon life cycle, habitat: of the river within the SAC, with including migratory passage through the estuary and up the river to spawning structure/ daily flows as close to what grounds, egg incubation in redds, fry and parr habitat quality and extent, and function would be expected in the downstream smolt migration. absence of abstractions and discharges (the naturalised flow). Flow in the upper Ehen, downstream of Ennerdale Water is affected by the weir at the outfall of Ennerdale and is subject to staged compensation flows during dry weather (Atkins & Gosselin, 2013) when the lake is below the weir crest level. Under the Water Framework Directive, the river Ehen (upper including Liza) is classified as a Heavily Modified Waterbody. Removal of the infrastructure at the top of the river Ehen would support a more natural
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) hydrograph and should lead to improvements in the river habitat and natural processes in the river. Any development which would alter the flow regime of the river or its tributaries would need careful consideration and design. Supporting Riparian zone Maintain a patchy mosaic of Dappled riparian tree cover is beneficial to salmon, in terms of physical habitat: natural woody and herbaceous habitat provision from roots encroaching in to the channel and combatting structure/ (tall and short swards) riparian excessively high temperatures caused by climate change. However, the function vegetation extent of tree cover needs to be optimised to provide suitable conditions for the whole characteristic biological community.
The Ehen has a good variety of riparian tree cover. The first few km downstream of the weir at Ennerdale Water are flanked by almost unbroken woodland on both banks. This gives rise to patchier overhanging tree distribution downstream of Ennerdale Bridge. It is believed that the current tree extent is suitable to provide a mosaic of habitats in the Ehen for both salmonids and mussels.
Over-grazing of riparian areas can have a dramatic effect on salmon habitat through nutrient enrichment and soil inputs to the river. Where removal of livestock is not an option, wide buffer strips should be fenced next to the river so there is more chance of sediment/nutrient capture before it reaches the river. Drained land allows water to enter rivers quicker meaning faster and more pronounced peak flows during rainfall events, usually with associated sediment and nutrient inputs. Supporting Sediment Restore the natural supply of Natural levels of coarse sediment supply are critical to the maintenance of habitat: regime coarse and fine sediment to the high quality juvenile and salmon habitat, maintaining spawning gravels and structure/ river within the SAC characteristic biotope mosaics. Excessive delivery of fine sediment, from the function catchment or artificially enhanced bank erosion, can damage gills, impair vision and cause siltation of spawning and nursery areas.
Coarse sediment delivery in the upper reaches of the SAC (between Ennerdale Water and the confluence with Croasdale Beck) was severely limited until the reconnection of Ben Gill in 2014. The reinstatement of coarse sediment delivery to this reach will help increase the quantity and quality of suitable spawning areas for salmonids. Ben Gill is an ephemeral stream so reconnection of this will also help to slightly improve the natural flow regime of the river during high flows. Sediment delivery from Ennerdale Water is still affected by the dam, and will continue to be until this and other infrastructure is removed from the top of this section. Any activity which seeks to remove coarse gravel or affect coarse sediment delivery to the river Ehen will require
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) consultation. Supporting Soils, Restore the properties of the The Ehen catchment is primarily farmed for cattle and so soil inputs likely to habitat: substrate and underlying soil types, including be prevalent within this catchment include slurry, fertiliser, medications structure/ nutrient structure, bulk density, total including antibiotics and chemicals such as sheep dip and herbicides. Much function cycling carbon, pH, soil nutrient status of the land is also drained to make it more productive leading to decreased and fungal: bacterial ratio, within water retention. In addition, urban areas within the catchment are relatively typical values for the supporting rural meaning a high incidence of septic tanks with the potential for organic habitat waste to infiltrate soils. Furthermore, compaction of soils from heavy farm machinery also has the potential to lead to a hard pan layer which stops water from infiltrating leading to increased surface run-off. None of these parameters are measured consistently throughout the catchment but are highly likely to be outside the natural values found in an unimproved catchment. Supporting Thermal Maintain a natural thermal Water temperature can affect egg development, fish survival, feeding and habitat: regime regime to the river subject to a growth. Dissolved oxygen becomes limiting at high temperatures, particularly structure/ changing climate, ensuring that where there are additional pressures such as siltation and nutrient enrichment function water temperatures should not which may lead to low dissolved oxygen conditions within gravels. This affects be significantly artificially the egg and alevin stages. Any activities which have the potential to change elevated the thermal regime of the river are discouraged.
Supporting Invasive non- Ensure any non-native species Species such as signal crayfish can have a serious effect on salmon habitat habitat: native species categorised as 'high-impact' in and can predate heavily on salmon juveniles if present at high densities. structure/ the UK under the Water Chinese mitten crab has the potential to migrate long distances up rivers and function Framework Directive are either damage marginal habitats used by both adult and juvenile salmon. rare or absent but if present are causing minimal damage to the Japanese knotweed (Fallopia japonica) and Himalayan balsam (Impatiens feature glandulifera) are both present within the catchment and can lead to increased bare ground and therefore sediment delivery to the river. These species, along with any other invasive non-native species present should be controlled to reduce this pressure on interstitial habitat quality. Supporting Water quality Maintain levels of acidity to those Salmon are highly sensitive to acidification stress. There are large blocks of Maberly et al. habitat: - acidification which reflect un-impacted coniferous forestry within the catchment but these are being managed (2016) structure/ conditions sensitively for wildlife. The Forestry Commission are part of the Wild function Ennerdale partnership and measures are being taken to replace coniferous stands near to the river Ehen with mixed-broadleaved habitat which is more natural to this sensitive area.
pH in the river Ehen appears to be rising slightly since 1976 (Environment Agency spot sample data); this may be due to sources of acidification from air Page 29 of 36
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) pollution falling (Maberly et al., 2016). Supporting Water quality Restore the natural nutrient In addition to the wider ecosystem effects of eutrophication that have a habitat: - nutrients regime of the river, with any detrimental effect on salmon habitat, enrichment can place salmon at a structure/ anthropogenic enrichment above competitive disadvantage, for instance relative to brown trout. Salmon are function natural/background efficient foragers that are adapted to low productivity environments, and concentrations limited to levels at increased productivity makes efficient foraging obsolete. Having a healthy which adverse effects on the salmon population in the Ehen is vital to Margaritifera margaritifera but an feature are unlikely. increased fish biomass beyond what an oligotrophic system should be able to sustain is a sign of excess nutrient enrichment.
Eutrophication and episodic pollution causes direct mortalities, whilst chronic pollution affects substrate condition through the build-up of excessive microbial populations. Salmon are particularly sensitive to reduced dissolved oxygen levels in the water column and within the gravel substrate of spawning redds (nests). Any activities which are likely to increase nutrient inputs to the river are to be discouraged. Supporting Woody debris Maintain the presence of coarse Woody debris is an important component of river habitat for salmon as well as habitat: woody debris within the structure the wider biological community. Woody debris provides shelter from high structure/ of the river channel flows and cover from potential predators, as well as changing gravel function distribution around the debris. Retention of woody debris in the river is encouraged, as long as it is securely pinned. Supporting Adaptation Restore the feature's ability, and As above in Table 1. Environment processes and resilience that of its supporting habitat, to Agency (2016); (on which the adapt or evolve to wider Some spawning habitat within the Ehen is still detrimentally affected by an British Standards feature and/or environmental change, either unnatural flow regime resulting from impoundment at Ennerdale Water, as Institution (2017) its supporting within or external to the site well as significant nutrient and silt inputs from agricultural and forestry land. habitat relies) The river Ehen salmon population is classed as “Probably at Risk” and will remain that way until at least 2021 (Environment Agency, 2016). Establishing whether salmonids are present in the densities expected in a sustainably recruiting mussel river in an oligotrophic system (British Standards Institution, 2017) would provide more confidence in our ability to assess whether the salmon population was sustainable or whether it might be vulnerable to loss of resilience in a changing environment. There needs to be enough available habitat in good condition to support the various salmonid life history stages to provide conditions suitable to support resilient populations. Supporting Air quality Maintain or, where necessary, The supporting habitat of this feature is considered sensitive to changes in air More information processes restore concentrations and quality. Exceedance of these critical values for air pollutants may modify the about site-relevant (on which the deposition of air pollutants to at chemical status of its substrate, accelerating or damaging plant growth, Critical Loads and feature and/or or below the site-relevant Critical altering its vegetation structure and composition (including food-plants) and Levels for this SAC Page 30 of 36
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) its supporting Load or Level values given for reducing supporting habitat quality and population viability of this feature. is available by habitat relies) this feature of the site on the Air using the ‘search Pollution Information System Critical Loads and Levels are recognised thresholds below which such by site’ tool on the (www.apis.ac.uk). harmful effects on sensitive UK habitats will not occur to a significant level, Air Pollution according to current levels of scientific understanding. There are critical Information System levels for ammonia (NH3), oxides of nitrogen (NOx) and sulphur dioxide (www.apis.ac.uk). (SO2), and critical loads for nutrient nitrogen deposition and acid deposition. There are currently no critical loads or levels for other pollutants such as Halogens, Heavy Metals, POPs, VOCs or Dusts. These should be considered as appropriate on a case-by-case basis.
Ground level ozone is regionally important as a toxic air pollutant but flux- based critical levels for the protection of semi-natural habitats are still under development. It is recognised that achieving this target may be subject to the development, availability and effectiveness of abatement technology and measures to tackle diffuse air pollution, within realistic timescales.
The Air Pollution Information System does not provide estimates of critical loads or level values for any of the designated features of the site. The catchment does not support significant heavy industry and air pollution is not thought to be an issue currently. The majority of nitrogen inputs to the river come from agriculture.
Any developments which may increase air pollution significantly would need to be carefully considered by Natural England and any developments which have the potential to significantly increase levels of dust which may settle in to the river should be discouraged. Supporting Conservation Restore the management Active and ongoing conservation management is needed to restore this British Standards processes measures measures (either within and/or feature at this site. There is the feeling that salmon numbers have declined in Institution (2017) (on which the outside the site boundary as the Ehen within living memory but an adequate assessment of fish densities IPENS (2014) feature and/or appropriate) which are necessary is currently lacking for the Ehen. The Ehen does not have a salmon counter English Nature its supporting to restore the structure, functions installed and so the only source of information are data from rod licences. (2004), Views habitat relies) and supporting processes Salmonid density in oligotrophic systems should not be high as this indicates about management associated with the feature enrichment and an ability of the system to support a higher than natural River Eden and/or its supporting habitats. biomass. The CEN Standard (British Standards Institution, 2017) points to densities of between 0.1-0.2 trout per m2 as being suitable in sustainably recruiting mussel populations. Assessments following the CEN guidance should be carried out over a number of successive seasons to assess fluctuations in salmonid populations and evaluate what the system is capable
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Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) of supporting bearing in mind its oligotrophic nutrient status.
Management of other pressures/threats which have the potential to affect salmon in the Ehen include control of invasive species, minimising aggravated sediment and nutrient inputs and reinstating a more natural flow regime with no impediment to fish migration from barriers such as weirs. All of the pressures are currently being managed/investigated.
Supporting Fisheries - Ensure exploitation (e.g. netting Controls on exploitation should include migratory passage within territorial Environment processes exploitation or angling) of Atlantic salmon is waters, including estuarine and coastal net fisheries, as well as exploitation Agency (2016) (on which the undertaken sustainably without within the river from rod fisheries. The Ehen is fished for salmon with a feature and/or compromising any components tendency for a good catch-release percentage (Environment Agency, 2018) its supporting of the SAC population, including due to positive engagement in the area. Poaching is known within the habitat relies) multi-sea winter fish and catchment, some instances resulting in prosecution. Removal of structures seasonal components of the such as Ennerdale Mill Dam in Egremont can remove some poaching adult run. pressure but fishing is likely to have a detrimental impact on salmon numbers in the Ehen, which is considered to be ‘Probably at risk’ (Environment Agency, 2016). Supporting Fisheries - Ensure fish The presence of artificially high densities of other fish creates unacceptably Geist et al. (2006) processes introduction stocking/introductions do not high levels of predatory and competitive pressure on juvenile salmon. The (on which the of fish interfere with the ability of the management aim is to provide conditions in the river that support a healthy, feature and/or species river to support self-sustaining natural and self-sustaining salmon population, achieved through habitat its supporting populations of the feature protection/restoration and the control of exploitation as necessary. Stocking habitat relies) represents a loss of naturalness and, if successful, obscures the underlying causes of poor performance (potentially allowing these risks to perpetuate). It carries various ecological risks, including the loss of natural spawning from broodstock, competition between stocked and naturally produced individuals, disease introduction and genetic alterations to the population.
The Ehen is an oligotrophic system with a wild fishery so fish stocking is prohibited. The system is unlikely to be capable of supporting non-native species due to its low nutrient status. Increases in the non-salmonid biomass is likely to be detrimental for salmon through increased competition (Geist et al., 2006). Supporting Fisheries - Ensure fish The management aim is to provide conditions in the river that support a processes introduction stocking/introductions do not healthy, natural and self-sustaining salmon population, achieved through (on which the of salmon interfere with the ability of the habitat protection/restoration and the control of exploitation as necessary. feature and/or river to support self-sustaining Stocking represents a loss of naturalness and, if successful, obscures the its supporting populations of the feature underlying causes of poor performance (potentially allowing these risks to Page 32 of 36
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) habitat relies) perpetuate). It carries various ecological risks, including the loss of natural spawning from broodstock, competition between stocked and naturally produced individuals, disease introduction and genetic alterations to the population. If salmon from other catchments are introduced via stocking there is also a potential risk that these individuals will not act as hosts for the freshwater pearl mussel (Margaritifera margaritifera), potentially leading to further decline in the pearl mussel population. Supporting Integrity of Maintain any habitats outside of Salmon populations are dependent on the integrity of sections of river processes off-site the site boundary upon which channel, riparian areas, and transitional and marine waters that lie outside of (on which the habitats the Atlantic Salmon population the site boundary. Headwater areas and tributaries do not fall within the site feature and/or may depend boundary, yet salmon use these areas for spawning and juvenile development its supporting and are critical for sustaining populations within the site. Fully developed habitat relies) riparian zones are essential for salmon habitat, yet none of the riparian zone is included in the site boundary, particularly if the river channel is operating under natural processes and moves laterally over time within the floodplain. The conditions experienced by salmon on their marine migration (through the saline transition zone, estuary, coastal waters and into the high seas) are critical to the well-being of populations within the river, and vice versa. Supporting Screening of Ensure any intakes and Salmon can be seriously affected by inadequate screening on their adult and processes intakes and discharges likely to trap a smolt migrations, as well as on their smaller juvenile dispersion movements (on which the discharges significant number of individual between spawning grounds and nursery areas. feature and/or salmon are being adequately its supporting screened. habitat relies) Supporting Cover of Maintain a sufficient proportion of In rivers where it naturally occurs, submerged and marginal vegetation is an processes submerged aquatic macrophytes to allow important element of juvenile salmon habitat. In oligotrophic, fast flowing (on which the macrophytes them to reproduce in suitable systems like the Ehen macrophytes, may not be that prevalent as they may feature and/or habitat and unaffected by river find it difficult to root and grow in these conditions. its supporting management practices. habitat relies) The Ehen does not support large macrophyte beds but small patches are available near suitable salmonid habitat. Supporting Water Restore water quality and Mussels and salmonids have overlapping habitat niches for water quality and processes quantity/ quantity to a standard which quantity requirements so much of the information provided for the ‘Water (on which the quality provides the necessary quantity/quality’ section for Margaritifera margaritifera is relevant to salmon feature and/or conditions to support the Atlantic also. Salmon eggs are particularly vulnerable to smothering by silt and low its supporting Salmon feature. dissolved oxygen levels in gravels caused by eutrophication. As such silt and habitat relies) nutrient inputs to the catchment should be reduced as much as possible.
In addition to allowing good interstitial flow, spawning gravels also need to be Page 33 of 36
Attributes Targets Supporting and Explanatory Notes Sources of site- based evidence (where available) stable so eggs are not displaced during high flow events. The upper Ehen is impacted by an unnatural flow regime because of the main dam at the outflow of Ennerdale Water. When abstraction infrastructure is removed, this will change the flow regime and therefore the gravel distribution within the system leading to a change in areas currently suitable/unsuitable for salmon spawning. This will need careful monitoring to assess if there are sufficient areas for salmon going forward. Version Control Advice last updated: n/a Variations from national feature-framework of integrity guidance: N/A
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