Spined Loach Survey of the Ouse Washes SAC and SSSI

Project Description

The Ouse Washes Special Area of Conservation (SAC) extends for a length of 63 km and an area of ~311 ha. The site is comprised of two parallel man-made drainage channels, namely the Counter Drain/Old Bedford River (CDOB; 33 km) and the Old Bedford River/River Delph (OBRD; 30 km), and there is also an extensive ditch network. The primary reason for the designation as an SAC is for the representative populations of spined loach (Cobitis taenia) within the Great Ouse catchment. The site is also listed under the Ramsar Convention as a wetland of international importance for a variety of breeding and non-breeding birds. The Ouse Washes SAC acts as a major land drainage for the surrounding area through the storage of flood water. Consequently, the washland is subject to regular flooding in winter and subsequent drainage via the OBRD.

The CDOB and OBRD represent two Site of Special Scientific Interest (SSSI) units and Common Standards Monitoring (CSM) was carried out in 2009, 2011 and 2016. The previous CSM assessments described the condition of the spined loach population in the CDOB as ‘favourable’ and healthy owing to its clear water and abundant macrophytes. Conversely, the condition of the population in the OBRD was assessed as ‘declining’ due to environmental pressures resulting in a lower mean density of fish and an absence of young individuals. Long-standing pressures impacting the site include inappropriate water levels at several times of year and sediment and nutrient pollution, which have had impacts on the extent and composition of vegetation and caused occasional incidences of low dissolved oxygen levels. Given the continuing pressures on the site, it is necessary to conduct a feature assessment for spined loach in the Ouse Washes SSSI/SAC, to inform Natural England’s:

1. Understanding of the conservation status of spined loach at the site, based upon previously monitored locations (CDOB, OBRD) and new areas (ditch network), which have not been surveyed.
2. Understanding of the environmental requirements of spined loach in the context of the operation of the SSSI/SAC as a flood storage area and the impacts of a managed hydrological regime.
3. Condition assessment for the Ouse Washes SSSI and SAC.