The Bothnian Sea is the southern part of the Gulf of Bothnia, and connects the northern most part of the Baltic Sea, the Bothnian Bay to the Baltic Proper. The salinity is the Gulf of Bothnia is relatively low, ranging from 6 psu in the southern part, to 5 psu in the north. The stratification is not as strong as in the rest of the Baltic Proper and the water masses get mixed during autumn and winter preventing the formation of oxygen poor bottoms. Also the nutrient load is smaller in the Bothnian Sea. The mean depth of the Bothnian Sea is 60 m, and the basin freezes over annually during the winter months. Hard bottoms dominate the basin, but soft sediments appear in the deeper parts.
The fauna and flora in the Bothnian Sea are a mix of marine and freshwater species, the latter of which are more abundant towards the north. Some marine creatures, like eel grass (Zostera marina), brown shrimp (Crangon crangon), and Baltic prawn (Palaemon adspersus) reach their limits of distribution in the Bothnian Sea. The benthos of the Bothnian Sea is characterized by a limited number of species, the most common of which is a glacial relict, the Baltic isopod (Saduria entomon). Other common species include Monoporeia affinis, a small amphipod, and Baltic clam (Macoma balhtica). The Bothnian Sea boasts many spawning and nursery areas for several species of fish, including herring, sprat, flounder, river lamprey and freshwater species, like grayling, vendace and whitefish. Salmon and sea trout used to be more plentiful in this sub-basin, but as is the case elsewhere else, they have declined severely in the last century because of the destruction of hatching rivers by damns and dredging. Many river stocks are now extinct and overfishing has continued to keep the rest down.
Sweden does not have plans to protect this area. But new opportunities might come as Sweden aims to protect 10% by 2020 of its marine waters.
