(above 50.000 fish annually in Klarälven alone), but decreased during the 1900s to critically low levels in the 1960s, resembling many large rivers around the world (Parrish et al., 1998; Piccolo et al., 2012). Until the days of hydroelectric exploitation, the catches (with far less refined catching methods) of salmonids in Lake Vänern alone were around 100 tons annually. In addition there were catches in several other rivers and tributaries (Ros, 1981). The annual total catch of Vänern salmon therefore then likely exceeded 100.000 fish per year (350 to 400 metric tons). These large, land-locked salmons are known to weigh up to 18 kg (40 lb) (Ros, 1981) in Lake Vänern. The Gullspång variant is now known as the larger and faster growing strain. Although that may have been different in the past, as from Klarälven there is historical information that a large and early-growing salmon stock, whose weight figure was between 8 kg and 17 kg, which it then reached while migrated up to its spawning grounds in the Norwegian tributary of Trysilälven. The world's largest registered landlocked salmon, exceeding 20 kg (44 lb), was also caught in nearby Lake Vättern in 1997, which was documented being of the Gullspång stock. A 23 kg (51 lb) specimen of the related species of brown trout ("Salmo trutta lacustris") has also been reported as being caught in the lake by local commercial fishermen (Ros, 1981). Gullspångsälven had, on the contrary, an early rise of smaller salmon (3–4 kg). This variant, called the “green ones” (“gröningen”), wandered through Lake Skagern up to the spawning grounds in Letälven. Of these 5 differentiated and separate strains of salmon in each of these rivers, both the spring-run fish in Gullspångsälven and the fall-run strain of Klarälven have both disappeared due to habit destruction (Ros, 1981). The early-running strain of large salmon that once spawned in the upper reaches in Norway is also extinct. It is believed that at least 3 other subspecies of landlocked salmon have also previously gone extinct in the lake - mostly due to the construction of hydroelectric power plants and dams. This unique type of freshwater salmon hence also once inhabited Norsälven and its tributaries (the Frykfors power plant was built in 1905, but salmon fishing did not end in the river until 1944 after the obligation to keep the salmon ladders in place was removed and Edsvalla power plant began