In the 1800s, annual catches in both Vänern and Klarälven were high (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).
In the 1800s, annual catches in both Vänern and Klarälven were high (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).
Nordberg, unpublished data],[Christensen 2009], [Runnström 1940] and [Ros 1981]).
In the 1800s, annual catches in both Vänern and Klarälven were high (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).
An increasing level of nitrogen had been problematic during the 1970s through 1990s, but is now being regulated and is at a steady level. Some bays also have problems with eutrophication and have become overgrown with algae and plant plankton. ==Fish== Vänern has many different fish species.
Other factors contributing to habitat deterioration include forestry & logging, agriculture, acidification of waters, pollution, road construction, fishing pressure, predators (mostly mink and cormorant - which are both accidentally introduced species) and climate change ([Nordberg 1977] and [Piccolo et al.
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.
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).
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).
Only Gullspångsälven and Tidan still have confirmed yet small self-sustaining migratory salmonid stocks left remaining coming from Vänern (Ros, 1981).
This is especially true in the Gullspång River - where it is believed that less than 1% of the natural smolt producing habitat remains in the surrounding watershed drainage system (Ros, 1981).
Nordberg, unpublished data],[Christensen 2009], [Runnström 1940] and [Ros 1981]).
This entire prevailing situation has also led to a negative impact on both of the remaining populations genetic diversity (Ros, 1981) and their unique yet poorly preserved traits, leading to their present endangered status. ===Other fish=== The most important large fish in the lake are brown trout (Salmo trutta) and zander (Sander lucioperca).
An increasing level of nitrogen had been problematic during the 1970s through 1990s, but is now being regulated and is at a steady level. Some bays also have problems with eutrophication and have become overgrown with algae and plant plankton. ==Fish== Vänern has many different fish species.
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.
But this procedure has by no means proven to be adequate in replacing the previous natural production capacity held in these waters, leading to a demise in both volumes and the overall quality of the remaining wild strains. The proportion of wild salmon and trout combined in the commercial catch in Vänern has increased from a maximum of 5% in 1997 (Fiskeriverket and Länsstyrelsen i Värmlands län, 1998) to up to 30–50% by 2008 (Degerman, 2008; Hållén, 2008; Johansson et al., 2009).
In the 1800s, annual catches in both Vänern and Klarälven were high (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).
But this procedure has by no means proven to be adequate in replacing the previous natural production capacity held in these waters, leading to a demise in both volumes and the overall quality of the remaining wild strains. The proportion of wild salmon and trout combined in the commercial catch in Vänern has increased from a maximum of 5% in 1997 (Fiskeriverket and Länsstyrelsen i Värmlands län, 1998) to up to 30–50% by 2008 (Degerman, 2008; Hållén, 2008; Johansson et al., 2009).
The Klarälv salmon historically migrated as far as 400 km upstream into Norway to spawn in the northerly sections of the river. These two sub-groups of salmonids are more related to the Baltic stocks than to North Sea stocks (Palm et al., 2012), and have both in their isolation distinctively developed in Lake Vänern for over 9,000 years (Willén, 2001).
In a 2002 report, the data showed no marked decrease in overall water quality, but a slight decrease in visibility due to an increase of algae.
But this procedure has by no means proven to be adequate in replacing the previous natural production capacity held in these waters, leading to a demise in both volumes and the overall quality of the remaining wild strains. The proportion of wild salmon and trout combined in the commercial catch in Vänern has increased from a maximum of 5% in 1997 (Fiskeriverket and Länsstyrelsen i Värmlands län, 1998) to up to 30–50% by 2008 (Degerman, 2008; Hållén, 2008; Johansson et al., 2009).
The increasing proportion of wild fish in the lake could be a result of (1) increased natural production and/or protection of wild fish, and (2) declining numbers and/or decreased survival of hatchery smolt (Eriksson et al., 2008).
2008; Swedish Board of Fisheries 2008).
A Viking ship was found on the lake's bottom on May 6, 2009. A story told by the 13th-century Icelandic mythographer Snorri Sturluson in his Prose Edda about the origin of Mälaren was probably originally about Vänern: the Swedish king Gylfi promised a woman, Gefjon, as much land as four oxen could plough in a day and a night, but she used oxen from the land of the giants, and moreover uprooted the land and dragged it into the sea, where it became the island of Zealand.
Nordberg, unpublished data],[Christensen 2009], [Runnström 1940] and [Ros 1981]).
But this procedure has by no means proven to be adequate in replacing the previous natural production capacity held in these waters, leading to a demise in both volumes and the overall quality of the remaining wild strains. The proportion of wild salmon and trout combined in the commercial catch in Vänern has increased from a maximum of 5% in 1997 (Fiskeriverket and Länsstyrelsen i Värmlands län, 1998) to up to 30–50% by 2008 (Degerman, 2008; Hållén, 2008; Johansson et al., 2009).
The Klarälv salmon historically migrated as far as 400 km upstream into Norway to spawn in the northerly sections of the river. These two sub-groups of salmonids are more related to the Baltic stocks than to North Sea stocks (Palm et al., 2012), and have both in their isolation distinctively developed in Lake Vänern for over 9,000 years (Willén, 2001).
In the 1800s, annual catches in both Vänern and Klarälven were high (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).
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