The Site is a representative North European coastal archipelago formed by 360 islands and islets with shallow marine waters, which provides an important breeding location for large numbers of seabirds and waterfowl. The Site supports nationally-threatened species such as the common tern Sterna hirundo, the black guillemot Cepphus grylle and the common guillemot Uria aalge, and there is also a considerable breeding population of the great cormorant Phalacrocorax carbo and of the European shag Phalacrocorax aristotelis. Other species that regularly use the site are the Eurasian otter Lutra lutra and the harbour seal Phoca vitulina. The vegetation on the main islands has been shaped by traditional grazing and harvesting, and the ceasing of these activities is very likely to trigger vegetational succession. The islands are also used for recreation and tourism. When they were inhabited, there was a strong traditional practice of collecting seabird eggs and eider down. Common eiders were provided with homes, often made from old boats turned upside down. Even though the islands are vacated today, this is still practiced to some extent, partly in order to preserve the character of the Site.