Little dart fish habitat survey 2017

Westcountry Rivers Trust Rain-Charm House Kyl Cober Parc Stoke Climsland Callington Cornwall PL17 8PH Telephone: Email: Web:

LITTLE DART CATCHMENT FISH HABITAT SURVEYS ALONG THE RIVERS:

LITTLE DART & STURCOMBE WATER 2017

A REPORT TO River Taw Fisheries Association â„… Blakewell Fisheries Muddiford Barnstaple Devon EX31 4ET Report prepared by: P. Turnbull BSc. (Hons.) & A. Dowding BSc. (Hons)

Report: Surveyors: Completed on: Authorised by:

Little Dart Catchment Fish Habitat Surveys 2017 Phil Turnbull BSc. (Hons.)

30/06/2017 Adrian Dowding

+44 (0) 1579 372 140 info@wrt.org.uk www.wrt.org.uk

Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017

EXECUTIVE SUMMARY Westcountry Rivers Trust was commissioned to conduct rapid walkover surveys along appropriate lengths of the Little Dart and the Sturcombe Water. The Little Dart was divided into three main sections: the lower Little Dart, upper Little Dart and Sturcombe Water. A total of 31.7km was walked, with fish habitat and associated river protection issues noted during the surveys in order to primarily assess spawning gravel condition for salmon and the connectivity of the river corridor for migrating salmonid fish.

The fish habitat is recorded and advice given on the present state of the fishery.

Recommendations and suggestions are provided for improvement if appropriate. A summary of the statistics gathered are displayed in the tables below.

The lower Little Dart presented two potential challenges to migration in the form of woody material accumulations: SS 71248 13646, and SS 72448 12939. The upper Little Dart presented six more significant potential migration barriers: four debris dams, a weir structure at SS 84814 16961, and a piped road bridge culvert at SS 85143 17620. The Sturcombe Water presented multiple debris dams, further details can be found in the report.

Throughout the Little Dart catchment sediment loading of the river bed, particularly within spawning gravels, is a major problem. This may be attributed to a wide range of land management techniques, including but not limited to: planting and harvesting of crops close to marginal habitat, bankside trampling from livestock access, unchecked contaminated runoff directly entering watercourses, excessive erosion of unstable and shaded banks. It is necessary to address such issues to ensure spawning gravels become or remain loose for effective spawning redd construction, and subsequent oxygenation of eggs within gravel nests. However, reducing sediment input into the Little Dart catchment requires continuous campaigning for and delivering of improvement works on the small scale, in order to have large scale positive impacts. Gravel cleaning in key areas, coupled with sensitive coppicing and habitat enhancement, may help in protection and bolstering of existing salmonid stocks.

Of particular note was the recording of what appeared to be an overflow pipe discharging directly into the lower Little Dart, at SS 68711 13867. The source of this overflow is unknown, however the close proximity to the Chulmleigh sewage treatment works raises concern as to the possible organic content of the discharge, and therefore requires investigation.

Riparian tree management was highlighted as a frequent factor regarding habitat degradation.

Large sections of the Little Dart catchment were heavily shaded with resultant lack of bank stabilising marginal growth, particularly in the upper reaches and throughout the Sturcombe Water. Where the river corridor is heavily shaded from dense, less mature specimens, minor coppicing to produce dappled shade on riffle and glide sections, and ~80% shading on pool areas will help increase productivity within shallow habitats traditionally inhabited by high densities of young salmonids, and increase holding area cover for returning adults. Elsewhere, a 50:50 shade to direct sunlight is recommended. Areas shaded from larger specimens may require more specialist attention if deemed a priority.

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Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017 Evidence of nutrient input was apparent throughout the survey, with dense algal growth in areas of sunlight and slow flows. Although a natural part of riverine ecosystems, excessive algal growth may increase risk of redd suffocation, and reduces available habitat for key invertebrate species. Therefore, any attempt to improve light penetration to the channel must coincide with works to reduce nutrient/sediment input. It is believed that the exclusion of livestock and sensitive management of arable soils would contribute significantly to improving the Little Dart fishery.

Table (i): Summary statistics for the River Little Dart catchment fish survey, 2017.

Little Dart River Habitat Fry Parr Glide Pool Modified Bedrock Chute Clean Spawning Silted Spawning Surveyed Length

Lower

3949.36 6824.40 3053.76 1715.36 224.25 137.94 22.65 218.90 1088.79 17097.47

Total Surveyed River Protection Bank Erosion/Direct sediment input Fenced bank Bank revetment Shaded Tunnelled Man-made fish migration obstacle present Natural/temp fish migration obstacle present Invasive plant species present on bank

Upper (m of river bed) 1741.75 3326.74 76.44 604.04 68.53 26.80 0.00 6.89 341.07 6165.46

Sturcombe River

2300.02 4759.13 36.07 633.19 92.48 75.74 9.80 0.00 638.85 8469.54 31732.47

(m of river bank) 2644.06

611.24

2020.86

11297.80 0.00 8401.37 2416.43

1984.99 0.00 4670.64 1792.60

4364.73 18.38 5396.36 1285.88

Yes, 1

Yes, 2

Yes, 2

Yes, (2) - see report

Yes, 4

Yes, multiple

Yes, extensive

Yes, extensive

Minimal

This survey is presented in G.I.S. (Geographical Information Systems – ArcView 10.2.2) format which accompanies this report. The report is supplied with a disk containing all the surveyed rivers electronically mapped.

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Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017

Sturcombe Water Lower Little Dart

Upper Little Dart

Figure (i): The Little Dart catchment rivers surveyed in 2017. Rivers surveyed to map fish habitat and associated river protection matters.

Table (ii): Recommended immediate actions for fish habitat improvements, 2017.

Location

Action

Priority

Lower L. Dart

Debris dam removal/realignment – 2 sites (Aug/Sept 2017)

1

Sturcombe

Debris dams removed/realigned – 6 sites (Aug/Sept 2017)

1

Upper L. Dart

Debris dam removal/realignment – 2 sites (Aug/Sept 2017)

1

Lower L. Dart, Sturcombe

Spawning gravels cleaned for 2017 season (Sept 2017)

1

Sturcombe, Lower L. Dart, Upper L. Dart

Selective Coppicing (Oct 2017 – Mar 2018)

2

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Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017 Location

Action

Priority

Sturcombe, Upper L. Dart

Debris dams removed/realigned – 8 + 2 further sites

2

Lower L. Dart Upper L. Dart

Man-made fish migration barrier assessment / easement (3 sites)

2

Sturcombe, Upper L. Dart

Stock exclusion fencing / buffer zone creation / alternative drink points

2

Sturcombe, Upper L. Dart

Wetland attenuation / buffer

2

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Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017

Contents Little Dart Catchment Fish Habitat Surveys, 2017

1. Introduction ................................................................................................................................. 1 2. Methodology ................................................................................................................................ 2 2.1 Fish Habitat Survey ................................................................................................................ 3 3. Results and Observations ............................................................................................................. 4 3.1 Lower Little Dart Fish Habitat Survey .................................................................................... 4 3.2 Upper Little Dart Fish Habitat Survey .................................................................................. 11 3.3 Sturcombe Water Fish Habitat Survey ................................................................................. 16 Anaerobic Digestion Plants .................................................................................................... 19 4. GIS results .................................................................................................................................. 20 5. Conclusions and Recommendations .......................................................................................... 21 5.1 Lower Little Dart .................................................................................................................. 21 5.2 Upper Little Dart .................................................................................................................. 24 5.3 Sturcombe Water ................................................................................................................. 26 References ..................................................................................................................................... 29 Appendices ..................................................................................................................................... 30 1.

Sturcombe Water Debris Dams .......................................................................................... 30

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Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017

Appendices

Appendix 1 – Sturcombe Water Debris Dam Photographs ...............................................................

Appendix 2 – Lower Little Dart ..........................................................................................................

Appendix 3 – Upper Little Dart ..........................................................................................................

Appendix 4 – Sturcombe Water .........................................................................................................

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Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017

1. Introduction Westcountry Rivers Trust was employed by partners including the River Taw Fisheries Association to investigate and present the state of fish habitat in the River Little Dart catchment.

The primary objective for the walkover survey was to locate and identify areas that may support successful Atlantic salmon (Salmo salar) spawning, either in current state or potentially, and note any connectivity issues that may act as physical barriers to migration of fish species.

Other key objectives for the survey were to provide information on how to reduce pressure on water quality through practical suggestions, relating to physical river protection measures and surrounding land use, and addressing issues and potential impacts on instream and marginal habitat.

The surveys were allocated a budget which dictated the length of river channel to be assessed.

The river basins chosen for walkover surveys included the Lower Little Dart (from the River Taw confluence upstream to West of Drayford), the Upper Little Dart (from confluence with the Sturcombe Water upstream to East of Rakenford), and the Sturcombe Water (from the confluence with the Little Dart upstream to Hares Down). A map of the surveyed rivers is presented in Figure 1.

Sturcombe Water Lower Little Dart

Upper Little Dart

Figure 1: The Little Dart catchment rivers surveyed in 2017. Rivers surveyed to map fish habitat and associated river protection matters.

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Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017 All rivers were surveyed during the late Spring of 2017, in good weather conditions, post a dry period to ensure adequate visibility of the river bed and habitats, and safe access throughout.

This also ensured continuous and efficient surveys were possible, maximising use of the available budget.

The aim of the walk-over survey was to gather information about the location and extent of various physical fish habitat features present in channel and the immediate surrounding area, to allow for assessment of habitat quality and quantity for salmonid fish species. Of particular interest was suitable habitat for salmon spawning and subsequent fry survival. The gathered information was then used to identify potential productivity limiting factors affecting salmon recruitment, informing recommendations for habitat protection and/or restoration measures.

2. Methodology The walkover surveys were conducted by Phillip Turnbull (Assistant Rivers Officer).

Access to the riparian habitat from landowners was obtained before commencement of surveys, through a system of cold-calls to farms and estates, followed by telephone conversations and various other forms of communication, to establish permissions. The River Taw Fisheries Association provided valuable help in establishing blanket permissions from their members.

The river survey was conducted by rapid walkover survey, undertaken primarily along the river banks and occasionally from in-channel, noting fish habitat types and associated river protection concerns.

The Lower River Dart section identified for surveying in 2017 was surveyed from the confluence with the main River Taw, upstream to Have’s Hill road bridge West of Drayford, surveyed over three consecutive days. The Upper Little Dart section identified was surveyed from the confluence with the Sturcombe Water to Lower Bulkworthy Farm East of Rackenford, completed as a one day survey. The Sturcombe Water section identified was surveyed from the confluence with the Little Dart to a point within Hares Down approximately 0.5km North of the A361 road bridge, surveyed over two consecutive days following the Upper Dart survey.

Fish habitat was recorded in accordance with the Westcountry Rivers Trust Survey Manual, which is based on the techniques outlined in the Environment Agency manual Restoration of Riverine Salmon Habitats – A Guidance Manual (Hendry and Cragg-Hine, 1997).

The presence or evidence of invasive plants species (Japanese knotweed, Himalayan balsam, giant hogweed and montbretia) was recorded. These species are an indicator of poor habitat management, requiring removal and controlled disposal. Positive habitat indicators were recorded, including presence or evidence of protected species and higher food chain predators.

Species such as otters (Lutra lutra), kingfishers (Alcedo atthis) and dippers (Cinclus cinclus) indicate good quality habitat and biodiversity.

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Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017

2.1 Fish Habitat Survey A suitably qualified officer visually assessed the watercourse for desirable habitat for Atlantic salmon (Salmo salar) and related anadromous species, sea trout (Salmo trutta), as well as other protected species associated with lotic systems.

The information gathered during rapid walkover assessments is used to identify river habitat diversity for fish, and subsequently inform selection of representative habitat for second phase fish surveys.

Habitat was recorded as per the criteria specified in Table 1. Non-differential GPS was not available for use during these surveys, however the scale used for the survey maps allowed for confident accuracy regarding manual recording of features. An online grid reference finder with detailed mapping was used for reporting purposes.

Table 1: Habitat type classification criteria

HABITAT TYPE

DESCRIPTION

Spawning Habitat & Silted Spawning Habitat

Ideally stable but not compacted, easily workable with a boot without generating excessive silt release, a mean grain size of up to 80mm for salmon. ‘Fines’ (<2mm grain size) to be less than 20% by weight.

Fry Habitat

Shallow = or <20cm deep, fast-flowing (50-65cm/s), with surface turbulence and a gravel (size range 16-64mm) and cobble (size range 64-256mm) substrate.

Parr Habitat

20-40cm deep, fast-flowing (60-75 cm/s), surface turbulent, with gravel/cobble/boulder (size > 256mm) substrate.

Glides

= or > 30cm deep, moderate velocity in range 10 – 30 cm/sec, surface smooth and unbroken, relatively even substrate of cobbles with finer material.

Pools

= or >40 cm deep, no visible flow, surface unbroken, substrate with a high proportion of sand and silt.

Bankside/Tunnel Vegetation

Riparian vegetation should ideally provide a mixture of open and closed canopy throughout the reach. Tunnel vegetation forms a complete closed canopy for extensive lengths. Where this occurs, evidence of past coppicing (multi-stems) or standards should be recorded

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Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

Macrophyte Beds

Extensive submerged and emergent macrophytes providing localised hydraulic diversity.

Obstructions to Migration

Impassable falls, weirs, bridge, sills etc. shallow braided river sections preventing upstream migration during low flows.

Modified Channel

Where the bank has been artificially modified, straightened, reinforced or reprofiled, for example to accommodate flood flow (includes culverts, concrete revetment, gabions, sheet piling etc.).

3. Results and Observations 3.1 Lower Little Dart Fish Habitat Survey A fish habitat walkover assessment of the lower Little Dart was conducted from the confluence with the main River Taw, to the road bridge West of Drayton. A reach of approximately 15km.

The surveys took place on the 17th, 18th and 19th of May 2017.

Silted Spawning Spawning 7% 1% Pool 10%

Fry 23%

Modified Channel 1%

Glide 18%

Parr 40%

Figure 2: Fish habitat percentages for the surveyed reach of the Lower Little Dart, 2017.

The primary factor considered for this section of the Little Dart was whether any significant migration barriers exist, in the form of woody material accumulations. Two areas were noted as presenting possible migration challenge. The first was a large windblown tree across the channel (SS 71248 13646) (Plate 1). Water levels were not notably different upstream and downstream of the apparent barrier, and therefore it is thought that ample space is available 4

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 underneath for water passage and subsequent fish passage. However, further investigation would clarify this, and may require removal action.

Plate 1: Large windblown tree at SS 71248 13646. May require removal or manipulation to a stable position that allows unhindered migration.

The second potential obstruction was located where the river channel divides in two around a small island, downstream of the bridge at SS 72462 13012. The obstruction is located within the left-hand channel (SS 72448 12939) (Plate 2). The right-hand channel is unblocked and provides an accessible migration route. The point where both channels re-join is marked as a pool, with no notable attraction flow either way during the assessed conditions. Increased flows, such as those that encourage upstream migration, may attract fish to the left-hand channel, and therefore may produce significant support for the removal of this material.

Some accumulations of woody material were noted, although not currently acting as any form of migration barrier and appeared stable. As part of a natural process woody material should remain in the channel unless causing flooding to property or blocking migration.

Small bedrock steps/ridges were noted, although these are not considered a migratory challenge for Atlantic salmon or trout, evidenced by historic spawning success throughout the catchment. A historic weir structure was found at SS 76745 13403, and appears to be broken through on the LHB (Plate 3). This structure is not thought to be a migration barrier in the current state, however if ever repaired, the structure would require assessment for fish passage.

A currently intact small weir structure was found at SS 77961 13607 (Plate 4). Although successful spawning has been recorded upstream of this structure, indicating increased flows ensure upstream passage over the weir, it may be worth surveying for ease of passage. The purpose of the structure is unclear, and is therefore thought to be historic use. Therefore, with correct agreement from all interested parties, it is recommended that the weir be dismantled in the future.

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Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017

Plate 2: Accumulation of woody material in the left-hand channel at SS 72448 12939. Requirement for removal dependant on attraction flows at point where channels merge downstream of blockage.

Plate 3: Weir structure at SS76745 13403. Left – the red box indicates part of structure presenting a migratory challenge. Right – the yellow box indicates where the structure is broken through, allowing passage in low flows. Higher flows would provide ample passage past this structure.

Plate 4: Small weir structure (purpose unknown) at SS 77961 13607

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Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 The in-channel habitat was diverse throughout the surveyed reach, with pool-riffle sequencing frequently encountered. Gravel riffles (Plate 5) suitable for Atlantic salmon (Salmo salar) spawning generally contained high levels of sediment. Concretion of gravels was rare, allowing for redd cutting by adult fish, however sedimentation was high enough to invoke concern over the survival of eggs and newly hatched fry. Brown trout (Salmo trutta) were observed throughout the survey, ranging from 1-6â&#x20AC;?, indicating successful recruitment of this sensitive salmonid species.

Exposed bedrock was notable in areas marked as parr habitat during the survey. The current gravel riffles are abundant, and dry gravel bars were frequent throughout the channel, however replenishment of these gravels in the future may be impeded by the apparent relatively rapid channel incision from high flows, and consequent reduction of adequate gravel recharge. This is not considered an immediate threat to recruitment, but is worth noting for future management options if future observations show increased bedrock patches and therefore decreased natural river bed recharge and gravel conveyance.

Plate 5: Gravel riffles suitable for spawning and fry habitat. Left: SS 69039 13717. Right: SS 69537 13590.

Of particular note was the colour of the river after a short period of rain (Plate 6). The second day of surveying (18th May) revealed a high sediment load after a relatively small amount of rainfall, evidenced by little to no change in flow. Although perception may be impacted by the contrast of bright and direct sunlight reflecting from suspended particles, compared to the

Plate 6: Indication of high levels of sediment input through increased turbidity post-rainfall.

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Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 previous day of cloud cover, the significantly increased turbidity of the water indicated high levels of sediment input.

Sediment input is a catchment-wide issue throughout the River Taw, and is related to a wide range of inputs. The Little Dart catchment walkover survey indicated various points for potential sediment input, primarily erosion of banksides and activity related to livestock farming. The soft clay banks of the Little Dart catchment are vulnerable to erosive pressure of increased flows, exacerbated by extensive land drainage and recent meteorological patterns of more extreme weather events. Erosion of banks is a natural process, however where bankside vegetation is either not allowed to establish through poaching by livestock, or left unmanaged and therefore over-shades and reduces vegetation of slumped banks, rapid erosion and consequent sediment input can cause in-channel habitat degradation. Due to the incision of the river channel, preliminary recommendations to reduce the rate of erosion include protection of banks with woody material structures and/or allowing slumped banks to vegetate by reducing shade and livestock access at key areas (Plate 7).

Plate 7: Top â&#x20AC;&#x201C; livestock access and over shading reducing marginal vegetation and increasing erosion vulnerability. Bottom â&#x20AC;&#x201C; restricted livestock access allows marginal and in-channel vegetation to establish, increasing bankside habitat for fish and invertebrates, and stabilising slumps to a more resilient vegetated slope.

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Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 Of further note was an overflow at SS 68711 13867 (Plate 8). The source for the overflow is unknown, however the water entering the river channel at this point was highly turbid, and is located next to the Chulmleigh sewage treatment works. Further investigation may be required to ascertain whether this input contains harmful effluent.

Plate 8: Overflow/input of high turbidity from unknown source SS 68711 13867.

Animal access was frequent throughout the survey. Several livestock/vehicle crossings were observed, with clear input of sediment at these points (Plate 9). Often cattle and sheep had free access to the river, and where fields were fenced drinking areas have become devoid of vegetation and provide an open route for contaminated run off. The nature of the poorly vegetated clay banks makes any animal access a potential input for sediments. Pasture pumps, gravity fed pipes from tributary streams, ram pumps or mains supply are valuable methods of reducing the impact of livestock grazing next to rivers. Due to the extensive nature of animal access and erosion throughout the survey, it is suggested that this is a major contributor to the sediment input witnessed.

Large sections of the reach surveyed were shaded by riparian tree growth, to the point of tunnelling over key fry recruitment areas. Shading is required to help with thermal regulation of flowing water, and is considered good cover for adult fish in pool habitat. However, extensive shading will reduce primary productivity and may impact fish populations through reduced trophic diversity. Management plans should include coppicing programs along riparian land, particularly focusing on allowing adequate light penetration on riffle habitat. Westcountry Rivers Trust recommends the 80:20 rule: 80% light and 20% shade on riffle habitat; 20% light and 80% shade on pool habitat. A general rule of 50:50 for reaches in between is thought to help with thermal regulation (Broadmeadow et al., 2011). Areas where the bank has slumped provide good potential for varied marginal species growth, and should therefore be managed to allow light penetration for natural stabilisation.

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Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017

Plate 9: Top – fenced livestock access points, indicating lack of vegetation and subsequent sediment input.

Bottom – livestock crossing points, highlighting traversal along the river channel in some areas, and high potential for heavy sediment loading.

Himalayan balsam (Impatiens glandulifera) was found throughout the survey of the Lower Little Dart. There were few large areas of Himalayan balsam growth, however frequent pockets of clumps were extensive. Woodland away from the river was often found to contain H.balsam, providing evidence of the significant challenge removal of this invasive plant species from the Taw catchment will be. Concentration of H.balsam growth reduced as the survey progressed upstream. Areas of livestock grazing access to the river bank edge had a clear effect on reduction of H.balsam growth. However, the extensive erosion and habitat degradation this can cause greatly limits the use of grazing as a control method. Furthermore, plants were still found where livestock has access, reducing the evidence of grazing as an effective method. Heavily poached ground was often found to be colonised by H.balsam.

On a more positive note, king fishers (Alcedo atthis), dippers (Cinclus cinclus), sand martins (Riparia riparia), and grey wagtails (Motacilla cinerea) were all observed along the lower Little Dart, as were brown trout of a range of sizes, indicating a functioning ecosystem. Hatching fly life was witnessed, with the associated flurry of rising trout in the evenings.

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Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

3.2 Upper Little Dart Fish Habitat Survey A fish habitat walkover assessment of the upper Little Dart was conducted from the confluence with the Sturcombe brook, to the East of Rackenford; a reach of approximately 5km. The survey commenced on the 23rd of May 2017.

Modified Channel 1%

Silted Spawning 6% Pool 10%

Glide 1%

Spawning 0% Fry 28%

Parr 54%

Figure 3: Fish habitat percentages for the surveyed reach of the Upper Little Dart, 2017.

The primary reason for conducting this survey was to locate and record fish habitat types, with special focus on spawning habitat. Gravel accumulations suitable for salmonid spawning were observed at regular intervals throughout the survey. Exposed bedrock became more common further upstream, however gravel riffles (albeit mostly dry) and berms existed all through the surveyed reach of the upper Little Dart. However, as with the lower Little Dart, gravels were sedimented. Concretion was rare, but high sediment loads were evident when gravels were disturbed. Pool habitat was present, as was an abundance of parr habitat; however, exposed bedrock substrate was common in areas marked as parr, with a few bedrock steps located inchannel. These were not noted as migration barriers. Brown trout were observed throughout the survey, in the range of 1-6â&#x20AC;?. Low flow conditions impact the availability of spawning gravels in many areas. The presence of frequent gravel berms provides evidence of some gravel movement, which may increase availability of viable spawning gravels after high flow events.

Migration barriers exist in the form of woody material, and historic constructed weirs. Debris dams were located at, in order from downstream: Downstream of Bradford Moor Hill bridge (SS 81959 16225), Upstream of Crow Lane bridge (SS 84107 16649), and two upstream of Springhill Down Hill bridge (SS 85274 17855, SS 85389 18057) (Plate 10). Significant potential spawning habitat exists upstream of the two dams most downstream, and therefore it is recommended that action be taken to ensure fish passage is not impeded by these accumulations. There was a weir 11

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 structure located upstream of Queen Dart Hill bridge, at SS 84814 16961 (Plate 11). Through visual inspection only, this structure is thought to be a significant challenge to upstream migration in low flow conditions. Due to the presence of potential spawning habitat upstream of this weir, 1

2

3

4

Plate 10: Debris dams located during walkover survey of the upper Little Dart. In order from downstream.

it is recommended a survey be undertaken with the aim to modify/remove the structure.

Plate 11: Weir structure located at SS 84814 16961. This structure is thought to be a significant challenge in low flows.

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Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

The road bridge where Springhill Down Hill crosses the Little Dart is constructed over a multiple pipe culvert (SS 85143 17620) (Plate 12). This structure is considered a potential complete blockage for upstream migrating Atlantic salmon and adult brown trout under the observed conditions. With increased flow, due to the funnelling effect of the piped culvert, and the enclosed nature, this structure will likely be a large deterrent for upstream migration. Although high up the catchment, and therefore upstream of abundant potential spawning habitat, increasing connectivity of catchments is important where fish stock recruitment has reduced to ensure maximum habitat is available. Therefore, future assessment may be necessary for appropriate action.

Plate 12: Piped culvert under the road bridge on Springhill Down Hill, SS 85143 17620. This structure is regarded a potential complete blockage to upstream migration of Atlantic salmon and adult brown trout, in conditions observed.

The sedimentation evident through the survey may source from erosion of exposed clay banks, and frequent livestock access (Plate 13). Erosion was frequently encountered, due to channel incision. Although an important natural process, providing channel morphological heterogeneity and exposed banks for species such as kingfishers, destructive access from livestock and overshading from unmanaged riparian tree growth often leads to excessive erosion with limited marginal vegetation regeneration. The result is unstable banks and poor riparian habitat, reducing species richness. Where bankside fencing exists, it was often erected too close to the river channel, restricting potential for riparian regeneration. Furthermore, livestock passage between unfenced fields has often created muddy quagmires next to the channel, creating the same sedimentation input as though access to the river was unimpeded. It is the assessment of this report, based on the evidence observed throughout the reach surveyed, that sediment input from accumulated land management practices is a major contributor to the sedimentation of fish habitats and requires addressing on a catchment scale. Buffer zones are a highly important method of reducing the impact from livestock on river channels, and increasing species richness throughout a catchment.

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Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

Plate 13: Examples of livestock access, and damage to riparian habitat leading to sediment input and reduced species richness.

However, in areas without livestock access erosion was still abundant, due to the nature of the incised clay channel. Sediment input is a natural process, and may be exacerbated by recent climatic changes to more extreme weather events. It is important to allow for bank slumps to vegetate and stabilise, creating low vegetated marginal habitat (Plate 14).

Large sections of the surveyed reach were over-shaded by riparian tree growth. However, in open areas there was evidence of nutrient input through filamentous algal growth on substrates in slow flow areas. Therefore, increasing light penetration at shallow areas may increase algal growth.

Furthermore, hemlock water dropwort (Oenantha crocata) growth was extensive in places, which can act to bind gravels and reduce spawning habitat. Any work to reduce canopies for light penetration should coincide with work to reduce nutrient input, and encourage land owners to manage potential spawning habitat if at risk of encroachment from hemlock.

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Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

Plate 14: Examples of regenerating marginal habitat. Left: vegetated and stabilising back slump. Right: Low bank with increasing species richness, in a field with evidence of historic grazing/current light grazing.

Himalayan balsam was still present, but noticeably less than in the lower Little Dart walkover survey. Growth was generally restricted to small clumps sporadically spaced throughout the reach surveyed. Having observed large, dense clumps in sloped woodland >20m from the river channel during the previous survey, this is not conclusive evidence of the limit of spread of this invasive species. H.balsam is often observed exploiting poached ground where native species struggle to colonise. Therefore, reduction of livestock access may result in colonisation of H.balsam if present in a catchment, and requires monitoring by land owners to ensure effective control is administered as part of any livestock restricting works.

An organic odour was noted from a muddy drainage ditch (SS 81915 16215), highlighting the potential input from land drainage that is not necessarily indicated as surface water on maps.

Ditches with exposed banks were observed throughout the surveys, acting as small but cumulative sediment inputs. These small sources were numerous, and have been marked on walkover survey maps. Surface water from such sources should ideally be drained into constructed wetlands to minimise sediment and organic input. Furthermore, a pipe with an adhoc join over a riffle was observed at SS 84393 16862, and may require investigation (Plate 15).

Plate 15: Left: muddy ditch with organic odour. Right: Unidentified pipe across riffle.

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Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

3.3 Sturcombe Water Fish Habitat Survey A fish habitat walkover assessment of the Sturcombe Water was conducted from the confluence with the Little Dart, to Hares Down, North of the A361; a reach of approximately 10km. The survey commenced on the 24th and 25th of May.

Modified Channel 1%

Pool 8%

Silted Spawning 8%

Spawning 0% Fry 27%

Glide 0%

Parr 56%

Figure 4: Fish habitat percentages for the surveyed reach of the Sturcombe Water, 2017.

The reasoning for the survey was as the upper Little Dart, to further identify viable spawning habitat in the higher catchment of the Little Dart river. Potential spawning gravels and fry habitat were found regularly spaced along the entire reach surveyed. Dry gravel berms were observed along most reaches, indicating good gravel movement through this part of the catchment.

However, as with the Little Dart, sedimentation was a frequent issue. The Sturcombe had a more uniformly wide channel than the upper Little Dart, with a number of significant pools interspersed by riffle and parr habitat. Thus, holding potential for upstream migrating adult salmonids is potentially higher in the Sturcombe than the upper Little Dart. Bedrock was exposed in many areas marked as parr habitat, however in-channel habitat diversity was generally of good quality.

General bankside erosion was more apparent in the Sturcombe Water than the upper Little Dart, indicating periods of high energy flows (Plate 16). Bank incision was fairly constant, with the majority of outside bends showing evidence of regular erosion. Exposed clay was frequent along the banks. Where banks were lower and light penetration allowed, riparian growth ensured more robust banks (Plate 17). There was extensive shading along the channel from riparian tree growth, which appeared denser than that encountered in the upper Little Dart. Opening of the canopy would benefit primary production at key riffle areas. Brown trout of 1-6â&#x20AC;? were observed throughout most of the survey, indicating sustained production within the system.

16

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

Plate 16: Regular exposed clay banks prone to erosive energy from high flow events. Though a naturally occurring morphological feature, excessive erosion can significantly increase sediment input to a system.

Plate 17: Example of light canopy and lower banks providing low growing riparian vegetation, with resulting more stable banks.

A number of potential migration barriers were recorded, primarily consisting of woody material dams, and one rock revetment (SS 83997 21320, photo ID SD11) past which brown trout were no longer noted during visual observation. The locations of the dams have been listed in Table 2, with corresponding photographs found in the appendices. Though all relatively small, the size of the channel means moderate accumulations can have significant impact. The priority has been allocated according to basic assessment of severity to migration in the encountered and estimated slightly increased flows. The last three obstructions were located North of the A361 in Hares Down, where viable spawning habitat appeared to reduce, and therefore are considered of low priority.

17

Westcountry Rivers Trust – Little Dart Fish Habitat Surveys 2017

Table 2: ID, location and priority of woody material dams encountered during the survey.

Photo. ID

Grid reference

Priority

Photo. ID

Grid reference

Priority

SD1

SS 81196 17942

High

SD8

SS 83050 20282

Med

SD2

SS 81366 18528

Med

SD9

SS 83556 21006

Med

SD3

SS 81413 18607

High

SD10

SS 83780 21219

Med

SD4

SS 81833 19542

High

SD11

SS 83887 21320

Med

SD5

SS 82041 19690

High

SD12

SS 84275 21513

Low

SD6

SS 82153 19785

High

SD13

SS 84401 21650

Low

SD7

SS 82402 19906

Med

SD14

SS 84447 21712

Low

Other potential obstructions include two hanging gates found at the downstream and upstream end of a deer fenced enclosure (Plate 18) (SS 83292 20706, SS 83432 20898). The downstream gate appeared to be of reasonable height from the river bed to allow for minimal impact on upstream migration. However, the upstream gate appeared very low and may provide a significant challenge for upstream migrating adult salmonids. The gravel accumulation on the left-hand bank may suggest this is due to the dynamic bed morphology, indicating the necessity to monitor all structures within a river channel in reference to migration blockage potential.

Plate 18: Hanging gates encountered during the Sturcombe brook walkover survey. Left: downstream of enclosure, looking upstream – gate height allowing fish passage. Right: upstream of enclosure, looking downstream – gate height may restrict upstream migration.

18

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 Animal access was frequent throughout the reach surveyed, and at times causing severe bankside erosion and sedimentation of local gravels. Large areas with no bankside fencing allowed unimpeded access with resulting extensive degradation of bankside habitat and stability, for example downstream of Crowdhole Hill road bridge (SS 81214 18098). Tracks and crossing points/fords with soft and vulnerable entry points will act as sediment inputs during crossing or rainfall events (Plate 19). Animal access in some form is inevitable, as a vast amount of deer crossing/access points were observed in wooded areas â&#x20AC;&#x201C; the extensive nature of shading from riparian trees makes traversal via the river corridor by large mammals likely, creating extra pressures from trampling. Therefore, it is important to keep livestock away from the river where possible with fencing and managed buffer zones of width >2m, with incorporated reinforced drinking areas where necessary.

Plate 19: Animal access and crossing points act as significant cumulative sediment inputs. Fencing with buffer zones >2m, light penetration for vegetation growth, and a hard substrate for drinking/crossing areas helps to reduce the impact from necessary land management practices.

The short section surveyed North of the A361 on Hares Down presented extensive riparian erosion and animal damage. The shading of the channel has restricted vegetation growth, and thus acts to intensify the issue. Significant sediment input at the upper reaches of a catchment may impact the whole system, and therefore it may be worth investigating further the state of the moor regarding sediment input to help protect valuable spawning habitat in the upper reaches.

Anaerobic Digestion Plants The presence of anaerobic digestion plants within the Little Dart catchment may signify a potential source of sediment input, through the growth of late harvested crops, such as maize or root vegetables. The late harvest of such crops can often coincide with wet weather events, therefore exacerbating sediment loss to water courses. Furthermore, late harvest without planting of an over-winter cover crop leaves large areas of exposed soil in the rainy season, with subsequent risk of erosion highly likely.

19

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

4. GIS results This survey is also presented in ArcView v.9.3 G.I.S. (Geographic Information Systems software) format and a disk containing all the surveyed rivers electronically mapped accompanies this report.

Table 3: Summary statistics for the fish habitat survey, Little Dart catchment 2017.

Little Dart River Habitat Fry Parr Glide Pool Modified Bedrock Chute Clean Spawning Silted Spawning Surveyed Length

Lower

3949.36 6824.40 3053.76 1715.36 224.25 137.94 22.65 218.90 1088.79 17097.47

Total Surveyed River Protection Bank Erosion/Direct sediment input Fenced bank Bank revetment Shaded Tunnelled Man-made fish migration obstacle present Natural/temp fish migration obstacle present Invasive plant species present on bank

Upper (m of river bed) 1741.75 3326.74 76.44 604.04 68.53 26.80 0.00 6.89 341.07 6165.46

Sturcombe River

2300.02 4759.13 36.07 633.19 92.48 75.74 9.80 0.00 638.85 8469.54 31732.47

(m of river bank) 2644.06

611.24

2020.86

11297.80 0.00 8401.37 2416.43

1984.99 0.00 4670.64 1792.60

4364.73 18.38 5396.36 1285.88

Yes, 1

Yes, 2

Yes, 2

Yes, (2) - see report

Yes, 4

Yes, multiple

Yes, extensive

Yes, extensive

Minimal

The fish habitat definitions are explained in Table 1 in the methodology section.

River protection issues are presented in the GIS package. Bank erosion was noted as banks with bare earth from recent slumping or wash away. Where areas are marked as unfenced, this generally depicts unfenced pasture where new fencing is likely to improve river protection by excluding livestock and consequently improving bank stabilisation through vegetation growth.

20

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 Man-made migratory obstacles are weirs which are primarily assessed to be impassable to any fish species at the low river flows encountered during the survey.

Fish migration is generally thought of as salmonid migration; however eel and lamprey migration was also considered. Natural/temporary migratory barriers to fish are mostly debris dams.

5. Conclusions and Recommendations A total of approximately 30km of river was walked during the Little Dart walkover surveys, 2017.

This distance is divided into three main sections; the lower Little Dart (15km), the upper Little Dart (5km), and the Sturcombe Water (10km). The range of potential impacts on migratory salmonid spawning was the same for each stretch surveyed, and therefore the recommended actions will be similar throughout the Little Dart catchment. The main focus of the surveys was to advise on the viability of migratory salmonid spawning. And highlight issues that adversely impact the longterm survival of resulting populations. The main issues identified were often directly related, and included: sediment input, bank erosion, migration barriers, unfenced river channel, unmanaged riparian trees and over-shading, and the invasive plant species Himalayan balsam.

For protection and enhancement measures to have a long term positive impact, it is important to engage with and support local land managers to accommodate fundamental river protection measures. A focus on reducing sediment input, and systematic riparian management, would significantly help in producing the desired outcomes, while also having the benefit of increasing flood water attenuation, improving livestock health, reducing land loss and erosion control costs.

5.1 Lower Little Dart The section of the lower Little Dart surveyed is located within a topographically varied valley, where the lower section consists primarily of wide and open farmland, which becomes significantly steeper with a much higher percentage of woodland further upstream.

Consequently, the Little Dart is prone to high energy spate conditions during periods of heavy rainfall, with flow conditions varying considerably even with short rainfall events. The steep-sided valley coupled with extensive woodland creates high risk of migration barriers in the form of woody material accumulations. >15 such barriers have been removed/manipulated in the last 3 years through Westcountry Rivers Trust and project partners and this survey shows the extent needs further attention to bring the woody debris back into good management.

Spawning Gravel riffles were noted at regular intervals throughout the Lower Little Dart survey, with good in-channel habitat diversity. Many riffles were situated up and downstream of pool habitat, increasing the holding potential for returning adult salmon and trout, and improving the hydraulic potential through the riffle â&#x20AC;&#x201C; an important factor when considering water flow penetration through spawning redds. However, gravels were generally sedimented, some significantly, from 21

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 catchment scale inputs. Concretion was not noted, with potential spawning gravels appropriately loose for redd cutting. Gravel cleaning operations â&#x20AC;&#x201C; use of jetted water to remove sediment and improve interstitial water flow for oxygenation â&#x20AC;&#x201C; may benefit in historically identified successful spawning areas, however with adequate rivers flows it is suggested that with reduced sediment input, current gravels could sustain successful spawning due to lack of concretion.

Areas of exposed bedrock were evident, suggesting evidence of more extreme weather events causing movement of gravels without effective recharge, however the frequency of encountered riffles and gravel berms give some confidence that spawning gravels are available to fish. It may be worth monitoring the movement of gravels to ensure observations match scientific data, however addressing sediment input is of higher value and suggested to be a more effective use of resources than gravel cleaning in the Little Dart catchment.

Connectivity Two potential woody material blockages were noted. The large tree across the river at SS 71248 13646 requires further assessment. Water is currently not backed up behind the tree, suggesting clear passage is possible under, around or through the bulk. Currently, the tree may be providing good habitat for a range of fish, invertebrates, birds and mammals, and unless causing a migration blockage, should be left in place due to clear stability. The material is at risk of accumulating and causing a blockage downstream over time, but reduction of the bulk to reduce potential for blocking migration may cause the tree to become dislodged. However, it may be prudent to address the tree sooner; proactively managing the woody debris, and use the material to create controlled local habitat features.

The debris dam downstream of Leigh bridge at SS 72448 12939 is currently blocking one of two channels, and therefore is not a total migration barrier. However, if the blocked channel is preferred by migrating fish through attraction flows, then this material should be removed. The local land owner on the left-hand bank has expressed interest in removal, and therefore may be able to mechanically assist for rapid removal.

A broken historic weir at SS 76745 13403 is not considered a migration barrier in current state.

This structure would require fish passage options if ever to be repaired.

A currently intact small weir structure was found at SS 77961 13607. Although successful migratory salmonid spawning has been historically recorded upstream, the purpose of this structure was not obvious, and therefore it is recommended for future removal.

Bank protection measures The lower Little Dart presented extensive areas of erosion, due to the incised nature of the clay banks. Livestock access was a regular occurrence, with large areas either unfenced or presenting broken/inadequate fences no longer restricting access. Areas with livestock access would benefit from fencing with >2m buffer strips, allowing stabilisation of banks from vegetation growth. A larger buffer zone is recommended in areas of severe erosion and high banks, to give allowance for future slumping and subsequent marginal vegetation growth. Protection of slumped banks 22

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 will increase the sustainability of field boundaries. Purpose built drinking points restricts bank damage by livestock, and controls access location; preferably away from potential spawning or steep, soft banks.

Some exposed vertical clay banks are important habitat for kingfishers and sand martins, and part of the natural environment in clay soil areas. Thus, in areas of less pressure where one high bank is opposite a low bank where high energy flows can dissipate, careful management to retain such habitat is possible. Protection of the bank toe, e.g. with woody material, may allow for reduction of banks side erosion while retaining some exposed clay banks. This should be coupled with good sized buffer zones with high light penetration for established rank grass growth, and managed low coppice, will help protect excessive erosion.

In areas of extensive shading, a decrease of the riparian canopy will encourage low vegetation growth to stabilise banks. Shade on pools is recommended, however shade from large trees may block light from the banks too. Suggested management for both objectives includes regular systematic coppicing of bankside trees by pools, allowing for young growth to shade the pools, while ensuring good light on the bank top, and fibrous root growth to hold the clay together.

Biodiversity Large and coarse woody debris structures act not only as bank protection, but increase available habitat for various fish cohorts, invertebrates, small mammals, and birds. In wide, straight sections where flow diversity is limited, large woody debris can be utilised to manipulate flows and increase heterogeneity. Careful placement of woody debris groynes can add to flow diversity, and protect vulnerable exposed banks. To avoid increasing potential flood risk, woody debris should be secured to the river bed or bank. Naturally accumulated woody debris should be assessed and either removed or secured, to ensure flow direction is managed to increase habitat, and simultaneously reduce flood risk.

Tree coppicing to increase light on riffle areas should be prioritised to increase primary production, and therefore support a higher density of migratory salmonid fry. Furthermore, site won woody material can be used to create habitat features in and around recruitment areas, increasing the juvenile habitat and consequently chances of survival to smoltification. Increasing bank side vegetation growth for stability will provide added riparian habitat for a range of animal species, and help reduce the impact of eutrophication.

Invasives Himalayan balsam was found throughout the lower Little Dart survey, sometimes in extensive clumps, particularly in wet woodland adjacent to the river. H.balsam was also noted in woodland 200m from the main channel (e.g. SS 71764 13284), indicating the extent of spread and difficulty in eradication. Concentration of H.balsam reduced further upstream, however it was often found colonising heavily poached ground.

Due to the nature of plant species categorised as invasive, growth and distribution can be rapid through a system, particularly where constant flowing water is involved. Therefore, the only 23

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 effective way to control invasive plant species is to coordinate a catchment scale management plan involving all affected parties, starting at the top of a catchment and working in a downstream, systematic manner. Although not guaranteeing total eradication, due to methods of dispersal including avian and anthropogenic transportation, working together in a logical fashion can significantly reduce the speed of spread to a much more controllable level.

Education is incredibly important, to ensure all affected landowners can recognise, and therefore treat before establishment, important invasive species in the area. The extent of the issue requires the involvement of the community, as tackling invasive plant species can be highly expensive in terms of resources and time. Angling associations and volunteer groups can be a highly valuable resource in combatting invasive species. Not only is the potential workforce significantly increased, eyes on the ground during the height of the growing season (e.g. during summer angling sessions) can provide important observations and reporting of where plants are growing.

However, it is worth stressing that some species, especially Japanese Knotweed, are classed as controlled waste, and therefore must only be tackled by authorised handlers and disposed of in the correct manner to ensure effective removal. Therefore, identification is imperative before any work commences, and further identifies the importance of working together with relevant authorities to tackle this ever-growing problem. The Devon Invasive Species Initiative has become the Non-Native Species Secretariat Local Action Group for the area, providing opportunity for national funding sources and engagement on a large scale. Westcountry Rivers Trust is committed to working with groups and communities to advise best course of action, and provide resources where possible to improve the habitats of West Country rivers.

Specific measures The overflow located at SS 68711 13867 requires investigation as a priority, due to the possibility of connection to the sewage treatment works (STW) on the RHB, South of Chulmleigh. Any input from the STW could have negative impact on water quality downstream of this point, impacting the local ecology, and potentially discourage upstream migration of sensitive fish species such as Atlantic salmon and brown trout.

5.2 Upper Little Dart The section of the upper Little dart surveyed is located within a more even valley that is much wider and consists of grazed farmland and woodland. Livestock access was a wide scale issue, as was over-shading from riparian tree growth. Consequently, erosion of banks was observed to be a major sediment input.

Spawning Similar to the lower Little Dart, the upper Little Dart presented frequent gravel riffles of good length and potential spawning habitat. Pool habitat was present to hold upstream migrating adults. Brown trout were observed from 1-6â&#x20AC;? throughout, in low density, indicating successful 24

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 spawning from a salmonid fish species. Gravel sizes were assessed as adequate for salmon spawning, with frequent gravel berms indicating a level of recharge through the system.

Sedimentation was again an issue, and appeared to be of similar scale than lower in the catchment, indicating sediment input is extensive throughout the system. As with downstream, gravels were not noted as concreted, and therefore likely to allow for redd cutting and subsequent local cleaning from the process. The colour of the river water post rainfall indicates high sediment loading from multiple sources, suggesting that efforts be made to reduce input above gravel cleaning operations, as any cleaned gravel is likely to become sedimented again quickly. However, trial areas may be a good way to test effectiveness for the future.

Connectivity Four debris dams require attention to ensure free passage and connectivity with the rest of the system. Location details can be found in section 3.2. The two furthest downstream are a priority due to significant potential spawning upstream.

A weir was located upstream of Queen Dart Hill bridge, at SS 84814 16961. It is recommended that this structure be assessed for fish passage in the future, with the aim to modify or remove to ease fish passage.

The piped culvert under the road bridge at (SS 85143 17620) is suggested to be a total blockage/severe impact to upstream migration. As part of catchment improvements, this structure should be assessed and appropriate action taken through the correct authorities.

Bank protection measures A level of erosion is essential to the natural functioning of river ecosystems, providing a source of nutrient and substrate for sediment inhabiting invertebrates and fish (e.g. brook lamprey, Lampetra planeri). However, it was noted that excessive erosion within the upper Little Dart catchment is contributing to habitat degradation. The main issue is uncontrolled livestock access, both into and close to the river channel. As stated above in section 5.1, bankside fencing in good repair that incorporates a buffer zone of at least 2m will help vastly reduce the impact of livestock on river banks, incorporating riparian tree/scrub management. Education on techniques and reasons is important, and continued engagement with land owners is necessary to promote the importance of riparian habitat, in light of ecosystem services (e.g. water quality) and protection of boundaries.

Working with local land owners to produce examples of good working practice, with the possibility of using funding from appropriate grants, may help show the long-term benefits of investment. Due to the catchment scale of the issue, advisory workshops with good working examples will hopefully help in the large-scale improvement of riparian management in the Little Dart catchment.

Biodiversity

25

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 As with the lower Little Dart, riparian tree growth is causing over-shading along large sections of the upper Little Dart, and it is therefore advised that selective coppicing be employed to improve in-channel production and thus species abundance. This should primarily be focused at areas of severe erosion, and fry riffle habitat.

Reduction of sediment input from riparian damage will improve in-channel habitat with expected subsequent increase in species abundance. Furthermore, woody material should be left inchannel, unless causing blockage to migration. In which case, the aim should be to retain woody material where possible, securing for use as habitat and possible use as flow deflectors to guide flow away from vulnerable banks â&#x20AC;&#x201C; this should only be attempted with proper consent and guidance from specialists. Westcountry Rivers Trust aim to provide advice regarding in-channel habitat manipulation.

Invasives Himalayan balsam was observed throughout the upper Little Dart, however in less densities than observed downstream. The most upstream extent was not identified due to the limitations of the survey, however a collaborative approach would be required to enact effective control. Livestock grazing appears to reduce densities of H.balsam, and may be incorporated as part of a management plan through controlled access to riparian habitat. However, excessive ground poaching enables H.balsam to colonise where native species struggle.

5.3 Sturcombe Water The Sturcombe Water is in many respects very similar to the upper Little Dart, sharing similar surrounding land use, geology and topography. Issues affecting the Sturcombe Water are also very similar to the upper Little Dart, with sediment input, over-shading and livestock access being the main potential factors leading to habitat degradation.

Spawning Potential spawning habitat was frequently encountered during the walkover survey, at regular intervals, with good lengths of fry riffle habitat. However, flows were very low, presenting evidence that the Sturcombe Brook is sensitive to low flow conditions regarding salmonid fry habitat availability. Often flow was restricted to small channels within gravel deposits, reducing the area for fry habitation. Brown trout were observed for the majority of the survey, from 1-6â&#x20AC;?, indicating successful recruitment of a salmonid species. Pool habitat was frequent, with presence of some significant pools suitable for holding of large migratory adult salmonids, next to potentially viable spawning habitat. The Sturcombe brook morphology appeared through visual observation to be highly suitable for Atlantic salmon migration and spawning with increased flows.

However, as with the rest of the Little Dart catchment, sedimentation of gravels was apparent.

Management suggestions mirror above recommendations, focusing on reduction of input over gravel cleaning operations.

26

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

Connectivity There were multiple debris dams located during the survey. Details of the locations can be found in section 3.3, with corresponding photographs in the appendices. It is recommended that these be removed, from the downstream end upwards. Although none of the accumulations are large compared with historic dams removed further own the catchment, they are of significant size when compared to the channel, and currently creating complete blockages to migration. A rock barrier, designed to retain a ford crossing, is providing total blockage to upstream migration (SS 83887 21320). No brown trout were observed upstream of this barrier. However, this is approaching the upper limit of migration in the catchment.

The hanging gates at the upstream point of an enclosure (SS 83432 20898) may cause migration restriction, and therefore it is recommended that the length be reduced. The downstream hanging gate is thought to currently allow passage.

Bank Protection measures The Sturcombe Water presented extensive bankside erosion, with heavy livestock poaching in places. Fencing with managed buffer zones is important to protect the river channel from sediment input, especially in upstream areas favoured by migratory salmonids for spawning.

Heavy local sedimentation was evident where livestock access was severe, indicating the importance of either controlled access through reinforced drinking areas, or pasture pumps and mains water supply. Westcountry Rivers Trust can advise on potential funding avenues for projects that aim to reduce the impact on local ecosystem services e.g. water quality.

As previously stated, continued engagement with local landowners is important to raise awareness of the impacts of river habitat degradation, and potentially work together for win:win situations.

Biodiversity As with the upper Little Dart, the Sturcombe Water was frequently heavily shaded from riparian tree growth. Coppicing would help to increase low level bankside vegetation, and improve production at key areas. Due to the extensive nature of shading in the catchment, the partnership with landowners is essential in improving the overall quality of habitat within the Little Dart catchment. Workshops and work party events would help demonstrate good working practice and methods to protect land, with the large benefits of working with a healthy environment has on livestock health and wellbeing.

Invasives Himalayan balsam was rarely observed along the Sturcombe Water channel, with individual plants identified within the lower reaches (pulled and hung to dry). Although it is unknown whether any further stands of H.balsam are present away from the river channel, visual evidence would 27

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017 suggest that H.balsam growth is currently minimal. Continued highlighting of the damage to ecosystem functions and services caused by H.balsam through networking and events will help reduce the likelihood of the invasive species spreading in the Sturcombe Water sub-catchment.

Although not a non-native invasive plant species, hemlock water dropwort (Oenantha crocata) was extensive in places, and can act to further bind gravel substrates reducing viability for spawning, and establish faster than other more beneficial marginal vegetation. The extensive growth of hemlock may be an indication of sediment and nutrient input, lack of significant increased flow events, and warm winter conditions reducing hard frosts controlling hemlock spread.

Rapid walkover survey techniques are limited to the river channel, and therefore the above is not a definitive list of potential inputs. The gathering of visual data enables further investigations into major or minor input sources to determine if potential sources identified are a significant risk.

28

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

References Armstrong, J.D., Kemp, P.S., Kennedy, G.J.A., Ladle, M. and Milner, N.J. (2003). Habitat requirements of Atlantic salmon and brown trout in rivers and streams. Fisheries Research. 62(2): 143-170 Broadmeadow, S.B., Jones, J.G., Langford, T.E.L., Shaw, P.J. and Nisbet, T.R. (2011). The influence of riparian shade on lowland stream water temperatures in southern England and their viability for brown trout. River research applications. 27(2): 226-237 Crisp, D.T. (2000). Trout and salmon ecology, conservation and rehabilitation (1st ed.). London: Blackwell Science Hendy and Cragg-Hine (1997).

Environment Agency

Restoration of riverine salmon habitats: A guidance manual.

Nislow, K.H. and Armstrong, J.D. (2012). Towards a life-history-based management framework for the effects of flow on juvenile salmonids in streams and rivers. Fisheries management and ecology. 19: 451-463 Pavlov, D.A., Emelâ&#x20AC;&#x2122;yanova, N.G. and Novikov, G.G. (2009). Reproductive dynamics. In T. Jakobsen, M.J. Fogarty, B.A. Megrey and E. Moksness (Ed.), Fish reproductive biology: Implications for assessment and management (pp. 48-90). Chichester: Wiley-Blackwell Pettine, M., Ruhhiero, A., Fazi, S., Buffagni, A., Anderson, J.M., Roncak, P. and Friberg, N. (2005). Organic pollution in rivers. In A.G. Solimini, A.C. Cardoso and A. Heiskanen (Ed.), Indicators and methods for the ecological status assessment under the Water Framework Directive: Linkages between chemical and biological quality of surface waters (pp. 99-116). Luxemburg: European Commission Directorate-General Joint Research Centre; Institute for Environment and Sustainability

This report has been produced in good faith with all reasonable skill, care and diligence based on the information provided and accessible at the time of its preparation and within the scope of the work as agreed with the client.

We disclaim any responsibility to the client and others in respect of any matters outside the scope of the above.

The report is provided for the sole use of the named client and is confidential to them and their professional advisors.

29

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

Appendices 1. Sturcombe Water Debris Dams SD1

SD2

SD3

SD4

SD5

SD6

30

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

SD7

SD8

SD9

SD10

SD11

SD12

31

Westcountry Rivers Trust â&#x20AC;&#x201C; Little Dart Fish Habitat Surveys 2017

SD13

SD14

32