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. The Site is the most important breeding area for seabirds in Nordland County. Bird cliffs on several islands harbour nationally red-listed breeding populations of Atlantic puffin Fratercula arctica (650,000 birds, constituting 3% of the global population), black-legged kittiwake Rissa tridactyla, razorbill Alca torda and common guillemot Uria aalge. On the skerries are breeding colonies of the great cormorant Phalacrocorax carbo, common shag Phalacrocorax aristotelis and black guillemot Cepphus grylle. The Site has a stable population of the nationally-threatened European otter Lutra lutra and common seal Phoca vitulina. It is 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.