Aquatic Survey Results

Aquatic Invertebrate Survey at River Wye SSSI, Symonds Yat, Herefordshire (June 2005)

The view looking up the Rapids

The view looking up the Rapids

Introduction

This report has been prepared following instructions received from Mr M Tyers, representing the British Canoe Union (BCU).

The BCU has recently purchased the section of the River Wye which includes a historic man-made island and adjacent rapids, the latter being utilised for canoeing activities.

The river is well-known for its dynamic character, with sharp fluctuations in level often occurring. The island is consequently undergoing constant erosion and it is therefore the intention of the BCU to compassionately restore its boundaries and allow sedimentation in order to restore plant growth and increase biodiversity. It is also proposed to divert more of the flow of water along the east side of the island, thereby allowing a more sedentary flow to the west.

A previous survey undertaken in September 2000 recorded fourteen species of aquatic coleoptera which included six species of Elmidae (Riffle Beetles). Of the six species, Macronychus quadrituberculatus and Normandia nitens are of Red Data Book classification, whereas Oulimnius troglodytes is Nationally Notable. A further Nationally Notable beetle, Pomatinus substriatus was also recorded from the west bank of the river.

Methodology

The recent survey was undertaken by Ron Carr and Garth Foster on 18th and 19th May 2005. Specimens were collected utilising a similar methodology to that employed during the 2000 survey, but adopting a quantitative rather than qualitative approach. A standard hand net of 20 apertures per 25mm was employed in bursts of approximately 30 seconds to 2 minutes. Three transects were carried out to include the banks of the main channel and the banks of the island, with two samples being obtained from the centre of the channel on either side of the island. Specimens were collected by kicking submerged gravel where possible in order to disturb resting invertebrates and netting around mossy boulders located at the water’s edge. Each site was sampled for thirty minutes by both recorders. A search for the white clawed crayfish Austropotamobius pallipes was also undertaken by turning over stones, though this proved unsuccessful.

Contained within this report are details of aquatic invertebrates recorded within the survey, particular attention being paid to the presence of Riffle Beetles (Coleoptera, Elmidae), Mayflies (Ephemetoptera) and Caddisflies (Trichoptera) several nationally important species of which are known to occur within the River Wye.

An inspection was also undertaken for accumulations of silt suitable for supporting colonies of the Depressed River Mussel Pseudanodonta complanata. Although an area of silt is present alongside the west bank of the main channel opposite the south end of the island, this proved to be only a few millimetres in thickness overlying a layer of cobbles, therefore not sufficient to support mussels. Dead shells of Pseudanodonta were recorded from two of the sampling sites, though these had probably been washed downstream from more suitable habitats.

Presentation of Results

A list of the surveyed sites together with brief descriptions is presented in Table 1. The approximate positions of the sites are denoted on Figure 1 and a list of the total number of species recorded in the survey is presented in Table 2.

The view below the Rapids

The view below the Rapids

Discussion

The survey has revealed that a diverse invertebrate fauna exists in the vicinity of the island and the margins of the adjacent river. Although the fauna of aquatic beetles is somewhat impoverished, the microhabitats provided within the immediate area have been found to support at least four Beetle species, one Mayfly and one Caddisfly of national importance.

Due to the naturally occurring, dynamic character of the river, it is considered unlikely that recreational canoeing activities are likely to have an adverse effect on the immediate environment and its associated invertebrate species.

Careful consideration should of course be given to the proposed restoration of the island, particularly with regard to accidental hydrocarbon pollution from contractors plant during the course of the work.

It is understood that stone gabions are being considered as a method of bank stabilisation, the utilisation of which would provide refugia for the invertebrate species.

Encouragement of sedimentation in local areas would also increase the possibility of colonisation by the mussel Pseudanodonta complanata and the beetle Oulimnius troglodytes. Of particular importance to the beetle population is the preservation of exposed root systems on the banks of both the island and the river, together with the inclusion of submerged, untreated timber in order to encourage larval development of such species as Machronychus quadrituberculatus and Pomatinus substriatus.

R.Carr BA (Hons) FRES.

Acknowledgements

I am indebted to Prof. Garth Foster, not only for his assistance with the survey itself but for his useful contributions in the production of this report. Sincere thanks are also conveyed to Craig Macadam, who identified the Mayfly larvae, Dr Ian Wallace for his determination of the Caddis larvae, and Thomas Huxley for confirming the Heteroptera identifications.

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