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Using “River Habitat Survey” to Plan Habitat Improvements for Fish
Mark Diamond, Marc Naura, Helena Parsons and Jim Walker
Environment Agency, PO Box 12, Warrington WA4 1HG, U.K.
Abstract
“River Habitat Survey”(RHS) is a standard method for capturing data on the physical habitat of rivers. It has been applied to in the order of 20,000 sites in the United Kingdom and elsewhere. It is accepted as a standard method for assessing “hydromorphology” to support the European Water Framework Directive.
This paper describes three examples that employ RHS as an aid to planning river habitat improvements for fish. The first two illustrate how RHS methods can be used to assess the needs of riverine habitat improvements for fisheries at different catchment scales and in different environments. The third example shows how RHS methods can then be used to assess the habitat improvements required for the management of different species communities.
The first example is the case study of the Sankey Brook, describing how RHS has been used to select coarse fisheries habitat improvement sites at the scale of a small urban catchment. Habitat modification, stream energy, geomorphological diversity and water quality were analysed during this site selection, and complementary geomorphological methods were used to design and implement appropriate habitat improvements.
The second example is a case study describing how RHS has been applied to plan where habitat improvements should be undertaken, and what those improvements should be, on the River Eden in North West England. The ultimate purpose of these habitat improvements was to increase the stocks of salmon and trout. Habitat modification, habitat quality and geomorphology were analysed to produce practical guidance on reach scale management options in the context of wider catchment objectives.
The third example describes the development, and subsequent application, of prototype broad-scale models that predict whether 500m sections of river will contain habitat suitable for target fish communities, such models may then be used to develop diagnostic tools for improving habitat for fish.
Introduction
There has been a rapid growth in the number of projects that aim to rehabilitate rivers and their corridors for fish and wildlife. In England and Wales, the Environment Agency alone invests in the order of £10 million per year on physical habitat creation and mitigation works intended to benefit fish and wildlife. With a few exceptions, these works are site-specific and involve relatively short sections of rivers (< 500 m) where land, funding and public support are available. The projects generally rely on intuitive, expert judgement to ensure that the design of the new habitats, and the techniques used, are appropriate in hydrological, geomorphological and ecological terms (Ward et al., 1994). Such tactical reach-based actions are rarely part of a catchment scale, ecologically sound, conservation strategy and therefore, there is some doubt that the actions significantly benefit the target species at a catchment scale (Frissell, 1997).
River Habitat Survey (RHS), (Raven et al., 1997; Fox et al., 1998), was developed to describe and evaluate physical habitat at national, catchment and lesser scales in England, Scotland, Wales and Northern Ireland. The analysis of RHS data has been used to support rationales for systematically selecting sites for rehabilitation at a catchment scale.
The aim of this paper is to describe three case studies that employ RHS as an aid to planning river habitat improvements. The first two case studies describe methods of using the RHS to identify appropriate locations for undertaking habitat enhancement. These examples contrast the selection of single sites (500m reaches) for localised but intensive habitat improvement in a small, low-lying urban catchment, with the identification of sub-catchments which will benefit from wider land use improvements at the scale of a large, upland rural catchment. The third case study shows how RHS methods can then be used to assess the habitat improvements required for the management of different species communities.
The first case study was undertaken on the Sankey Brook where RHS has been used to select coarse fisheries habitat improvement sites. Habitat modification, stream energy, geomorphological diversity and water quality were analysed during this site selection, and complementary geomorphological methods were used to design and implement appropriate habitat improvements. The second case study is on the River Eden, where catchment-wide evaluation has been used to produce suggestions for improved habitat management practises with the ultimate aim of increasing trout and salmon stocks. The third case study describes the development, and subsequent application, of broad-scale models that predict whether 500m sections of river will contain habitat suitable for target species of fish, and the potential development of prototype models to develop diagnostic tools for improving habitat for fish.
Case Study One: The Application of RHS to select sites for Fisheries Habitat Enhancement on the Sankey Brook
Introduction
This RHS application, described in Walker et al (1998), was undertaken as part of the 'Sankey Now Project'. This venture is a collaboration between local people, the Environment Agency, local government bodies and regional charitable bodies, focusing on the River Sankey and its tributaries (approx. 200 km of watercourse) which form a sub-catchment of the River Mersey in North West England. This small, low-lying catchment is dominated by urban and agricultural land use and has a history of poor water quality. It is currently of limited value as a recreational fishery, although the extensive urban context and good access to watercourses in many places means that there is strong local support for fisheries habitat improvements.
Methods
A comparison of RHS data for the Sankey with the national database identified that the catchment was severely degraded with extensive habitat modification and low habitat quality and was a priority catchment for rehabilitation. RHS data was then used to target such works effectively, producing a suite of possible rehabilitation sites. This acted to support the decisions of catchment managers on focusing rehabilitation in two ways; firstly, in identifying sites where enhancement was most needed, and secondly, in selecting sites where works would create optimum habitat benefits.
The targeting process comprised a catchment-wide assessment of existing geo-morphological diversity, stream power, water quality and habitat modification scores (HMS) based on RHS data. The criteria for site selection was high modification, low geomorphological diversity (and therefore low habitat diversity), fair water quality and moderate stream power (and thus adequate energy for natural development to occur after rehabilitation works had initiated change).
Results
A suite of six potential sites that fulfilled the criteria above were selected and after discussion with local Environment Agency Fisheries Officers a site on the Black Brook (a tributary of the Sankey) was chosen. Works undertaken at this site were designed and implemented using geomorphological assessment that complemented the RHS work. The enhancements at the site comprised relatively low cost rehabilitation works including the instatement of riffles, deflector and drop-weirs to encourage scour pool development and planting, (examples of features introduced are shown in figure 1 below). These introductions provided substrate, bedform and channel-margin habitat improvements. Roach were stocked at the site by Environment Agency Fisheries Officers, and subsequent monitoring has observed not only the bedding-in of the rehabilitation works, but also the maintenance of a developing fish community around the introduced habitat features.
Figure 1: Examples of Habitat rehabilitation undertaken at
the Black Brook
Case Study Two: The Application of RHS to Assist the Planning of Habitat Improvements on the River Eden
Introduction
The aim of this study was to assess whether habitat on the Upper River Eden and its tributaries needed to be improved and, if so, where habitat improvements where required and what form these improvements should take.
The River Eden, Cumbria, rises on limestone fells, flowing over calcareous limestone and sandstone before entering the Irish Sea at the Solway Firth. River water quality is high throughout the catchment and the Eden provides excellent salmon fisheries. The Eden and sub-catchments are designated as a candidate Special Area for Conservation (SAC) for salmon and other species.
This paper reports on the initial study and that included a 10km reach of the River Eden (between Appleby and Kirkby Stephen) and the following tributaries: Hilton Beck, Belah, Scandal Beck, River Eamont and River Lowther.
Methods
The main river and all tributaries were divided for sampling into 500m long sections and a stratified random sample of RHS sites was selected. The number of RHS sites sampled represents 57% coverage of the study area.
A geomorphological audit (Walker, 2001) was applied to the whole study area (excluding the Eamont). The geomorphological audit records the variety, extent and stability of depositional features and sources of erosion. Barriers to migratory fish, artificial features and floodplain land use were recorded. Fencing, livestock access, grazing pressure, shading of channel and evidence of pollution and siltation were also recorded. All surveys were undertaken in August-September 2000.
RHS summary statistics for the Eden were compared with summary statistics from the RHS database for Cumbria County, North West of England and the UK. RHS indices for assessing habitat quality, habitat modification and an overall index of river habitat quality were also calculated (methods described in Raven et al., 1998 and Parsons et al 2000a).
The extent of erosion and deposition recorded by the geomorphological audit was summarised into three classes (low, medium, high). The extent of different types of erosion, natural and accelerated, were investigated within the study area. Pressures within the study area were investigated by examining causes of accelerated erosion, land use, grazing pressure, pollution and modification to the channel and banks.
Results
This section describes a selected sub-set of results; a full description can be found in Parsons et al (2001a).
Is the habitat of the River Eden in need of improvement?
Habitat Quality Assessment (HQA) (Raven et al., 1998) is derived from RHS data and can be used to compare habitat quality on the River Eden with other sites. The distribution of HQA scores of the Eden sites in relation to a sub-set of sites from rivers similar to the Eden, sites within NW region and the baseline network (6,000 sites distributed across the UK) are presented in Figure 2. The surprising finding (given its cSAC status) is that habitat quality on the River Eden compares poorly with the other data sets. The River Eden distribution is skewed towards low HQA scores whereas the other datasets are skewed towards high HQA scores. It can be concluded that the habitat of the River Eden is in need of improvement.
Habitat quality Assessment Scores
Where are habitat improvements required?
A further analysis of HQA reveal a striking contrast in the level of habitat quality between the Lowther and Eamont sub-catchments and the main stem Eden, Scandal Beck, Hilton Beck and the Belah.
· HQA is predominantly classes 1 and 2 within the Lowther.
· Habitat quality is predominantly fair to poor in the Eamont.
· All sites on the Eden main stem have very poor habitat quality (HQA class 5).
· Very poor habitat quality (HQA class 5) is dominant within Scandal Beck and Hilton Beck and the upper reaches of the Belah.
What habitat management should be undertaken?
An analysis of the sub-scores that make up HQA for the Eden sites compared with other sites is shown in figure 3. The potential need for habitat management is indicated where there are large differences between the sub-scores for the Eden sites and those for similar sites. The largest differences indicated a lack of tree cover and poor bank vegetation structure.
Figure 3: Comparison of HQA sub-scores on the Eden catchment with
sites of similar type, NW region and UK baseline sites.
Analysis of the geomorphological data revealed that ‘natural’ processes were the most significant cause of erosion at all of the catchments, accounting for approximately 90% of erosion across the study area, (as shown in figure 4). However, it is not possible to rule out the impacts of land management on the underlying drivers of erosion e.g. the impact of soil compaction on hydrology. Of the ‘artificial’ processes only poaching contributes to the erosion figures to any real degree.
Management Recommendations
The main management recommendation that came out of this analysis was that the river system should be fenced selectively (largely on Scandal Beck, Hilton Beck and the upper reaches of the Lowther) to exclude livestock. This would lead to assisted natural recovery of within channel habitat, bankside vegetation structure and, if set back from the bank top, tree cover. This treatment may reduce the development of slides, slumps and other forms of bank mass-wasting.
Case study three: the Development and Application of Broad-Scale Models based on RHS to predict the occurrence of fish communities
Introduction
The purpose of this work was to determine whether RHS data could be used to predict the likelihood of specific fish communities being present or absent in standard RHS sites. The ultimate aim was to develop a model that could be used to prescribe how reaches could be modified to favour particular fish communities.
Methods
The methods used are described in detail elsewhere (Bergeron 2001, Naura, et al 2003). Electric fishing surveys and River Habitat Surveys were carried out at 95 sites on rivers in the Severn Catchment in the English Midlands. Correspondence Analysis was used to assign the seventeen species caught into predominant fish communities. Spearman’s rank correlation and binary logistic regression were used to explore which RHS variables were most closely associated with the predominant fish communities. Such data was supplemented with available map derived data (eg altitude, slope, height of source) and chemical and biological General Quality Assessment (GQA) data. These analyses were used to derive the models using methods described elsewhere (Bergeron 2001, Naura et al, 2003).
Certain elements of the broad-scale models were then used to explore a perceived habitat-related problem on the River Aire, North East England. Anglers were concerned that roach and dace fishing was in decline within a 15km section of the Aire. Local Environment Agency officers perceived that this was a habitat problem. A study was undertaken to test this hypothesis. RHS was applied at 15 regularly spaced sites along this section. This was supplemented by map derived data and electric fishing data, as for the Midlands study above. The data collected was then analysed as follows:
RHS summary statistics were used to present a general overview of habitat quality and modification. Discriminate analysis was used to determine which fish community should be present at each site if habitat was unmodified. The logistic model derived for the Midlands fish communities was applied using RHS data from the 15 sites to determine which fish communities the observed “habitat” would be predicted to support. These outputs could then be compared with the observed distribution of fish communities.
Results
Midlands Fish Community Analysis:
The Correspondence Analysis indicated 5 fish community types; these were communities dominated by dace, eel, gudgeon, roach and trout, respectively. Each of the logistic regression models indicated a significant association between RHS variables and the presence or absence of the fish communities. The features most closely associated with the presence of the dace community were weirs, submerged tree roots, and ripple flow. Features associated with the absence of this community were reinforced bank, steep bank profile, shallow river gradient and the presence of reeds. The gudgeon / chub community was most positively associated with GQA biology and improved grassland and negatively associated with gentle bank profile, vertical undercut and GQA chemical. The roach community was most positively associated with glides, runs, GQA chemical and silt and negatively associated with exposed boulders, riffles, submerged tree roots and GQA biological. The presence of the trout community was strongly associated with pools and riffles and its absence was associated with GQA chemical, extensive filamentous algae and smooth flow.
Management Application: the River Aire
Analysis of RHS statistics demonstrated that the majority of sites on the River Aire were of poor quality with high modification. The entire length showed evidence of re-sectioning with reinforcement on 50% of the banks. The occurrence of positive and negative features associated with the fish communities (as demonstrated by the logistic regression analysis) was abstracted from the RHS data and is illustrated in Figure 5. The highest probability of occurrence would be were 100 % of the positively associated features were found and none of the negatively associated features. On that basis it can be seen that the river is fairly unsuitable for trout communities, is highly suitable for gudgeon communities with no obvious pattern in suitability for the other two communities.
Further analysis indicated that the most likely communities to occur at each site was as follows: dace communities at the upstream and downstream limits (site 20783 & 22120), roach community at 22119 and the gudgeon community at all other sites. This matches the anglers perception that fishing was poor for roach and dace between the limits of the 15 km section.
It is speculated on the basis of the available evidence that following re-sectioning a number of decades ago and following a more recent reduction in channel maintenance, habitat is recovering naturally. It is predicted that as river recovers trout will become the dominant community.
Positive and Negative Habitat Features for Fish Communities in the River
Aire
Discussion of Case Studies
The methods incorporated in all three case studies described above incorporate either directly or indirectly two scoring systems based on expert judgement; Habitat quality assessment (HQA) as used on the Eden and Habitat Modification Index (HMI) as used in the Sankey application and indirectly in the Broad-Scale Fisheries Model. The criticisms of these two scoring systems and others like them are well rehearsed, (Kondolf 1995; Raven et al., 1998). While we acknowledge these criticisms as valid, their significance depends to an extent on how the scoring system is applied. The scoring system is neither used to set the objectives nor is it used to decide upon the prescription for habitat improvements. It is merely used to assist in the setting of reach scale objectives that can be used as a driver for physical habitat management on a catchment scale. The objectives would be set according to careful consideration of the RHS data and other information in the context of a rationale or strategy. In the case of the Eden analysis RHS was supported by geomorphology data and the rationale for habitat improvement was provided by the salmon action plan. Therefore the criticism of the scoring system per se while valid is not significant.
The use of livestock exclusion, as recommended for the Eden, is an approach to river habitat management that is widely reported (eg Evans 1993, Trimble, 1994, Environment Agency 1998). It has previously been applied on the Eden with mixed success. The benefit of the analysis using RHS has been that the problem can be quantified in terms of extent and precise location. To support the River Eden Salmon Action Plan (Environment Agency, 2000),the Lowther will be given priority as this is the most important tributary for the spawning of Spring salmon.
In terms of all three of the case studies discussed above, it should be emphasised that RHS samples are 500m reaches. Therefore, it was recognised that if the methods worked they would predict whether the 500m contained suitable habitat rather than developing a precise definition of habitat suitability.
There is a need to develop many more catchment ecological strategies that can be tested by application taking corrective action as knowledge and experience builds. While case studies one and three are aimed at improving coarse fisheries habitat, the second case study represents the largest investment of the three examples described above and this is targeted at the improvement of habitat for salmonids. It is also noted that the strategies of this kind currently applied in the UK are aimed at the conservation of the Atlantic salmon, (Milner et al., 1998 and Milner et al., 2000). Catchment ecological strategies from elsewhere are also aimed at the conservation of economically important salmonids.
In summary the three case studies described show that RHS methods can be used to locate suitable areas for habitat improvement at a catchment or sub-catchment scale, to identify (albeit coarsely) fisheries communities that are likely to occur and to suggest whether habitat improvements are appropriate at those locations. The case studies could be used to suggest the first two stages in a ‘3-stage model’ for fisheries habitat enhancement that is illustrated in figure 6 below, i.e. the identification of areas for habitat improvements and the determination of appropriate methods of improvement. The logical ‘3rd stage’ in this model is a strategy for implementation. In both the cases of the Sankey and the Eden this was either undertaken by liasing with local Environment Agency Fisheries Officers, or presenting the findings of the RHS analysis to the Environment Agency Area Office to support their existing management strategies. However, there is a need to develop such strategies at a national scale for fisheries enhancements and other habitat improvements, and this work is currently being undertaken as the development of Physical Quality Objectives for all rivers in England and Wales, (Walker et al 2002). PQOs are an Environment Agency Corporate Target that are being developed by the River Habitat Survey team.
| Stage 1: Identify areas in which to focus habitat improvements. |  Example
1: Sankey – Single sites within a small catchment |
|
 Example
2: Eden – reaches and sub-catchments within a larger area. |
||
| Example
1. Sankey - Complementary geomorphological design |
||
| Stage 2: Determine what sort of improvements should be implemented. |  |
|
 Example
3: Broad-Scale Model – Assess ‘missing’ and ‘impacted’ habitat features
for different fish communities. |
||
| Stage 3: Develop a strategy for implementing habitat improvements. | ||
Figure 6. A proposed ‘3-stage Model’ for Fisheries Enhancement.
References
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Raven, P.J., Fox, P.J.A., Everard, M., Holmes, N.T.H.and Dawson, F.H. 1997. ‘River Habitat Survey: a new system for classifying rivers according to their habitat quality’, in Boon, PJ and Howell, D.L.(Eds), Freshwater Quality: Defining the indefinable?, The Stationery Office, Edinburgh, 215 – 234.
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