River Ehen SAC Conservation Objectives Supplementary Advice
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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 Page 1 of 36 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] Page 2 of 36 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. Page 4 of 36 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