Røstøyan is a large archipelago with hundreds of islands, islets and skerries surrounded by shallow marine waters. Vedøya and Storfjellet are the two largest islands. There are bird cliffs located on several islands, with breeding populations of Atlantic puffin (Fratercula arctica), black-legged kittiwake (Rissa tridactyla), razorbill (Alca torda), common guillemot (Uria aalge) and northern fulmar (Fulmarus glacialis). On the skerries are breeding colonies of great cormorant (Phalacrocorax carbo), European shag (Phalacrocorax aristotelis) and black guillemot (Cepphus grylle). The Site has a stable population of harbour seal (Phoca vitulina). It is traditionally used for collecting seabird eggs, and is also popular for sports, fishing and boat tours. The area has three protected archaeological and cultural heritage sites such as Skomvær lighthouse. A long-term research project on seabirds led by the Norwegian Institute for Nature Research has been ongoing for 40 years in the research station at Hernyken.