Lake Vanern

The Lake Vänern (Swedish pronunciation: [&# 39;vɛːnɛɳ]) is the largest lake in Sweden, Scandinavia and the third largest in Europe, with a surface area of 5648 km² and located 44 m a.s.l. no. m.. The average depth is 27 m and the greatest depth is 106 m.

Lake Vänern is part of the Göta Canal and is connected to the North Sea/Kattegat along with Gothenburg on its west side and to Lake Vättern by the Göta Canal.

Etymology

The origin of the name is unclear, and subject to various hypotheses. One of them states that Vänern comes from Mar (Væni in transcripts from the 1100s, in documents called Lacus Wener from 932).

On the other hand, Venir is considered to be an interpretation of the old Swedish word vænir, with links to the words “friend hope" and 'trustworthy', 'beautiful' friend. Another possibility is that vænir was associated with an old name for the Göta river, Van "hope".

In general, interpretations are uncertain and the name may be several thousand years old, and linked to the now infamous words.

History

The southeastern part of Vänern is a depression that seems to have arisen from the erosion of Paleozoic-age sedimentary rock during the Quaternary glaciation that reached the area. This erosion would have reexposed parts of the Subcambrian peneplain. Because the southern and eastern shores are parts where the Subcambrian peneplain dips gently to the north and west respectively, the lake is fairly shallow in these places. The western shore of the lake largely follows a fault scarp associated with the Vänern-Göta Fault.

The modern lake was formed after the Quaternary glaciation about 10,000 years ago; when the ice melted, the entire width of Sweden was covered in water, creating a strait between the Kattegat and the Gulf of Bothnia. Because the subsequent postglacial rebound exceeded the simultaneous rise in sea level, Lake Vänern became part of Lake Ancylus which occupied the Baltic basin. Vänern was connected to Lake Ancylus by a strait at Degerfors, Värmland. Further uplift caused lakes such as Vänern and Vättern to be cut off from the Baltic. As a result, there are still ice age species not normally found in freshwater lakes, such as the amphipod Monoporeia affinis. On May 6, 2009, a Viking ship was found at the bottom of the lake.

A story told by Icelandic mythographer of the 13th century Snorri Sturluson in his Prose Edda about the origin of Mälaren was probably about Vänern: the Swedish king Gylfi promised a woman, Gefjon, as much land as four oxen could plow in one day and one night, but she used oxen from the country of the giants, and also uprooted the land and dragged it out to sea, where it became the island of Zealand. The Prose Edda says that "the inlets of the lake correspond to the headlands of Zealand"; since this is much more true of Vänern, the myth was probably originally about Vänern, not about Mälaren.

The battle on the ice of Lake Vänern was a battle of the VI century recorded in the Norse sagas and referred to in the Old English epic Beowulf. In Beowulf, it is stated that Vänern is near the location of the dragon's mound in Earnaness.

Geography

The lake is relatively shallow and covers a slightly oval area of 5,655 km². It has a glacial origin and in its interior there is a small archipelago.

The average depth of the lake is 27 meters and the maximum depth is 106 meters. Vänern shares a strait between Kållandsö in the south and Värmlandsnäs in the north in a western and an eastern part. The western part of the lake is called Dalbo Sea, and the eastern part is called Värmland Sea.

Vänern is a part of the Göta river waterway—Vänern- the canal and the closest links to the North Sea/Skagerrak at Gothenburg, by the Göta river on the southwest side and Karlsborg by Vättern via the canal.

Fish

Vänern has many different species of fish. Locals and government officials try to enforce fishery preservation projects, due to threats to fish habitat. These threats include water culture in tributaries, pollution, and M74 syndrome. Sport fishing in Vänern is free and unregulated, both from shore and from boats (with some restrictions, eg a maximum of three salmon or trout per person per day). Commercial fishing requires a permit.

In the open waters of the Vänern, the most common fish is the honeyfish (Osmerus eperlanus), which dominates in the eastern Dalbosjön, where the average is 2,600 smelts per hectare. The second most common is the Vendace (Coregonus albula), also more prominent in Dalbosjön, with 200-300 fish per hectare. Populations can vary greatly between years, depending on the temperature, level and quality of the water.

Salmon

Lake Vänern supports two subgroups of ground salmon Atlantic salmon (Salmo salar), known locally as Vänern salmon ("Vänerlax&# 3. 4;). Both are indigenous to Lake Vänern and all parent fish must spawn in the adjacent running waters to ensure their survival and produce offspring. The first subgroup is named after an eastern tributary of the lake, Gullspångsälven, hence the name Gullspång salmon ("Gullspångslax"). The second variety is the Klarälv salmon ("Klarälvslax"), which spawns mainly in the drainage system of the Klarälven River, which is more than 500 km long. Historically, Klarälv salmon migrated up to 400 km upstream towards Norway to spawn in the northernmost reaches of the river.

These two salmonid subgroups are more closely related to Baltic populations than to North Sea populations (Palm et al., 2012), and both, in isolation, have developed distinctively in Lake Vänern during more than 9,000 years (Willén, 2001). They are also very remarkable in that they have never entered the ocean and instead followed the deglaciation of Sweden's inland watersheds at the end of the Last Glacial Period. In the 1800s, the annual catches in both the Vänern and the Klarälven were high (more than 50,000 fish per year in the Klarälven alone), but they declined during the 1900s to reach critically low levels in the 1960s, which which resembles many great rivers in the world (Parrish et al., 1998; Piccolo et al., 2012). Until the time of hydroelectric exploitation, the catches (with much less refined catching methods) of salmonids in Lake Vänern alone were about 100 tons per year. In addition, there were captures in other rivers and tributaries (Ros, 1981). Therefore, the total annual catch of salmon from the Vänern was probably in excess of 100,000 fish per year (between 350 and 400 metric tons).

These large ground salmon have been known to weigh up to 18 kg (40 lb) (Ros, 1981) in Lake Vänern. The Gullspång variant is now known as the largest and fastest growing strain. Although it may have been different in the past, since there is historical information from Klarälven that a large and early-growing salmon population, whose weight figure was between 8 kg and 17 kg, which it reached when it migrated to its homelands spawning in the Norwegian tributary of Trysilälven. The world's largest recorded landlocked salmon, over 20 kg (44 lb), was also caught in nearby Lake Vättern in 1997, and was documented to be from the Gullspång stock. A 23 kg (51 lb) specimen of the related species of brown trout ("Salmo trutta lacustris") has also been reported taken from the lake by local commercial fishermen (Ros, 1981). In Gullspångsälven, by contrast, there was an early increase in smaller salmon (3-4 kg). This variant, called the "greens" ("gröningen"), wandered across Lake Skagern to spawning grounds in Letälven. Of these 5 distinct and separate strains of salmon in each of these rivers, both the Gullspångsälven spring strain and the Klarälven autumn strain have disappeared due to habit destruction (Ros, 1981). The early-running strain of salmon that once spawned in the upper reaches of Norway is also extinct.

It is believed that at least 3 other subspecies of freshwater salmon also previously became extinct in the lake, mostly due to the construction of hydroelectric power plants and dams. Thus, this unique type of freshwater salmon once inhabited Norsälven and its tributaries (the Frykfors power station was built in 1905, but salmon fishing did not end in the river until 1944, after it was removed the obligation to maintain the stops for salmon and the construction of the Edsvalla power station began), Byälven and its tributaries (which became extinct in the 1950s due to the construction of the Jössefors power station and the absence of the obligation construction of fish ladders) and at Borgviksån (a new power station was built next to the upper Borgviksån falls in 1939, without a fish ladder being built, thus blocking access to upstream spawning grounds).

The large and unique populations of lake brown trout found in Lake Vänern, which are also extinct, include populations originating from drainage systems arriving via Norsälven, Byälven, Upperudsälven, Åmålsån, Borgviksån, Lidan, and at the outlet of the lakes the rapids near Vargön (such as a very special type of trout that spawns downstream and is locally called "Vänerflabben). Only in Gullspångsälven and Tidan are small populations of self-sufficient migratory salmonids from Vänern confirmed (Ros, 1981). Klarälven populations are artificially maintained by human transport to spawning grounds above 9 power stations and the migratory brown trout population here is nearly extinct. However, most of these once unique landlocked salmon subspecies found in Lake Vänern have disappeared forever from the face of the earth due to human incursions. There are also other species of salmonids (common char, arctic char, and grayling) found in the lakes, rivers, and streams that connect them. Some of these lake brown trout isolates are large and genetically unique, although they are also severely threatened today (Ros, 1981).

Negative environmental changes to waters that support juvenile salmon (which have specific demands for clean, running water in their "pre-lake stage", which lasts from 1 to 3 years) have had an unintended effect on the production of natural smolts which now enter the lake. This is especially true of the Gullspång River, where less than 1% of the natural smolt-producing habitat is thought to remain in the surrounding catchment drainage system (Ros, 1981). Both salmon and trout are also highly dependent on being able to reach their spawning grounds, which is currently very limited following the construction of numerous dams in both river systems. Other factors contributing to habitat deterioration are forestry and logging, agriculture, water acidification, pollution, road construction, fishing pressure, predators (mainly mink and cormorant - which are introduced species accidentally) and climate change ([Nordberg 1977] and [Piccolo et al. 2012]).

Therefore, it is believed that the global production of natural smolts is today well below 10% of the previous production and capacity of Lake Vänerns ([P.O. Nordberg, unpublished data], [Christensen 2009], [Runnström 1940] and [Ros 1981]). Therefore, the lake's salmon and trout populations are today largely dependent on smolt farming, which are also released into the lake and some of its tributaries each year ([Swedish Fisheries Council (Fiskeriverket)], [Fortum (the hydropower operating company)], [Värmland County Administrative Council (Länsstyrelssen I Värmland)] and [Statistics Sweden (SCB, http://www.scb.se)]. this procedure has not been found to be at all suitable to replace the previous natural production capacity of these waters, which has caused a decrease both in the volumes and in the general quality of the remaining wild stocks.

The proportion of wild salmon and trout combined in the commercial catch in Vänern has increased from a peak of 5% in 1997 (Fiskeriverket and Länsstyrelsen i Värmlands län, 1998) to 30-50% in 2008 (Degerman, 2008; Hallén, 2008; Johansson et al., 2009). The increase in the proportion of wild fish in the lake could be the result of (1) increased natural production and/or protection of wild fish, and (2) decreased numbers and/or decreased availability. survival of hatchery smolts (Eriksson et al., 2008). Since the current Lake Vänern fisheries are completely dependent on hatchery production, improving hatchery smolt survival rates could increase catch rates. However, recently declining catch rates of hatchery-raised salmon and trout across the country have raised concerns about the condition, or 'quality', of the smolts that are released (Eriksson et al. al. 2008; Swedish Board of Fisheries 2008). Power companies, bound by clearing duties due to licensing verdicts, have also struggled to release a higher percentage of one-year-old fish, as opposed to the more natural two-year cycle. All this prevailing situation has also caused a negative impact both on the genetic diversity of the remaining populations (Ros, 1981) and on their unique, albeit poorly preserved, traits, which has led to their current endangered status.

Other fish

The most important large fish in the lake are brown trout (Salmo trutta) and walleye (Sander lucioperca). The most important small fish is the stickleback.

In Vänern there are five species of white fish: <It is necessary to find the correct scientific names for these species! -->

• Coregonus pallasii (also common in the Neva, Gulf of Finland, Baltic Sea)
• Lacustre white fish (white fish)Coregonus megalops)
• Coregonus maxillaris (population known mainly in the vicinity of Sweden)
• Coregonus nilssoni
• White fish of Valaam (Coregonus widegreni)
• Coregonus maxillaris