The Gullspång salmon are a relict, landlocked population of Atlantic salmon, trapped in Lake Vänern for about 8,000 years. They are fast growing and the largest of present landlocked salmon in the world and can grow to weights of over 20 kg. The Gullspång river also accommodates a lake-migrating trout, which can grow to the same maximum weight as the salmon. However, human activities and the damming of the river for hydropower have caused their populations to decline. The only remaining spawning areas are on the last 5 km of the river, close to lake Vänern. Before the damming the migrating fish could spawn more than 70 km from Vänern.
To protect the fish and the environment, a nature reserve was established here in 2006. Other measures have been taken including improved water regulating regime, restored spawning habitats, and regulations of the fisheries in lake Vanern. To provide the fisheries, significant quantities of farmed (adiposal fin clipped) salmon are released into Lake Vänern each year. Efforts are also being made to preserve the genetic material through captive breeding.
The Gullspång salmon and trout live as parr in the river for 1-3 years before migrating to Lake Vänern to grow and mature. They leave the river in spring at a water temperature around 10°C (50 F). 2-4 years later they return to spawn in october and november. The population size are very low for salmon (20-40 pairs) and low for trout (60-100 pairs). Ongoing monitoring includes electrofishing for parr, smolt traps and counting of returning spawners. Every year, results are presented in reports and published on the webpage www.gullspångslaxen.se.