The estuaries and shallow embayments of Britain and Continental western Europe lie in the migration path of about 25 million waterfowl which breed in northern Europe, western Siberia, Spitsbergen, Iceland, Greenland and parts of the Canadian Arctic. Most depend in varying degrees on the rich food resources of the intertidal and shallow sublittoral zones. In mid-winter the estuaries support 3-4 million waders, 250,000 Shelduck, Tadorna tadorna, and a high proportion of the 3.3 million ‘dabbling’ ducks present in north-west Europe.