A strategy for baseline monitoring of estuary Special Protection Areas

Intertidal estuaries in north-west Europe provide essential feeding grounds for internationally important numbers of overwintering shorebirds. Monitoring of the food supply available in these intertidal habitats is central to shorebird conservation strategy. In this paper, we describe the methods used to do a baseline survey of the Exe estuary Special Protection Area, south-west England. A grid system of sampling, linked to the Ordnance Survey National Grid, was used to ensure a systematic and repeatable coverage of the whole estuary. Cluster analysis was used to classify sites according to their invertebrate biomass densities. Classification of sites into groups was verified using environmental correlates. Results from these analyses were used to map habitat patches for the whole estuary. We show how, once a baseline survey such as this has been undertaken, monitoring of shorebird food supplies over time should be achievable with reduced sampling effort.