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Surveys of Falmouth Bay to St Austell Bay Special Protection Area (SPA) Winter 2020/21 (NERR111)

The Falmouth Bay to St Austell Bay Special Protection Area (SPA) is a large site covering a large marine area as well as shallow sandy bays, an estuarine area and part of a tidal river. The site was first designated in 2017 with qualifying interests for the site including wintering populations for black-throated diver, great northern diver and Slavonian grebe.

APEM Ltd were commissioned by Natural England to undertake two high-resolution digital aerial surveys of the open sea area of the SPA to monitor the populations of the qualifying features in February and March 2021. The survey design included 32 transects spaced 1 km apart and covered approximately 60% of the sea surface of the survey area.

The two surveys recorded a total of 6,719 and 7,149 birds and 77 and 65 marine mammals. Population estimates of the qualifying features were produced including apportioned individuals identified to relevant species groups (e.g. unidentified diver species) and peak counts from the last five years of Wetland Bird Surveys in the estuarine/creek areas of the SPA (made available by the British Trust of Ornithology). The peak population estimate was 27 for black-throated divers, 395 for great northern divers and 12 for Slavonian grebe/black-necked grebe. No Slavonian grebe individuals could be differentiated from black-necked grebe and these were only recorded in the February aerial survey.

Black-throated divers were observed in low numbers in this study compared to previous shore-based counts, although previous studies indicate how variable the population size is within and between seasons.

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NERR111 Edition 1 Surveys of Falmouth Bay to St Austell Bay SPA Winter 2020/21, PDF, 9.6 MB 2022/10/04