The fish fauna of the Baltic Sea reflects its 9 KY history of Arctic and temperate conditions and is a mixture of species that have invaded from the Atlantic and the continental watersheds. In spite of the challenging environmental conditions, such as low salinity in the entire Baltic Sea and varying temperature conditions, limiting the possibilities for successful reproduction, the number of species is comparably high.
Except for the Baltic Ice Lake and certain stages of the cold Yoldia Sea and freshwater Ancylus Lake, the fish fauna of the Baltic Sea, as recorded by archaeological and historical notes, has to a large extent remained unchanged. Some freshwater and cold-water species such as Arctic char may have disappeared while others, such as fourhorned sculpin and eelpout, have adapted and persist as “ice age relicts.” There are few viable introductions of novel species; the round goby may be the most conspicuous invasive species. The extinction rate is still low; the loss of sturgeon and the common skate within the HELCOM (the Helsinki Commission) area is due to fishing, and, for the riverine sturgeon, due to damming.
Since the formation of the Baltic Sea, fishing has played an essential role in supplying coastal settlements and their hinterlands and in trading. The archaeological and historical records have indicated fishing conducted with varying intensity using different methods.
Herring fishing has been a significant economic driver from the Middle Ages onward. Recent archaeological findings indicate that organized fishing was established at the outer archipelagos along the present Swedish east coast on predominately herring and cod archipelagos for self-sufficiency shortly before or during the Viking Age, and later to engage in barter.
The fact that the cod abundance has sometimes been sufficient for letting cod fishing be the most important fishery in the northern Baltic Proper alongside the fishery on herring may indicate that the eastern cod stock had relatively high productivity even when the Baltic Sea was significantly less eutrophic than it has been since the mid-20th century. This preindustrial variability in cod abundance suggests that climatic changes leading to changes in inflows of oceanic water may have affected salinity levels in the Baltic Sea.
Fisheries show substantial variability, especially over the last century. Fish production may have increased due to nutrient enrichment of the Baltic Sea. Higher yields have also been obtained due to higher fishing intensity and technological changes. Fishing has, therefore, become a major driver in shaping fish stocks.
The eutrophication of the Baltic Sea, leading to higher primary productivity and increasing water temperature and reductions in ice cover, may have led to changes in ecosystem structure and productivity. It should be underscored that such changes may also be amplified by the increasing fishing pressure on the cornerstone species such as herring, leading to significant disruptions in the food web.
