Bleka is a very special Atlantic salmon. It and the Namsblanken are Norway's only surviving relict salmon strains.
The Bleka was almost extinct in the late 1960s, but much has been done to save it.
What is a relict salmon?
A relict salmon never goes to sea, but lives its entire life in fresh water. Bleka is a relict Atlantic salmon.
Photo: Bjørn Barlaup, NORCE
Byglandsfjorden. By Store norske leksikon/Statens kartverk. License: NLOD (Norwegian license for public data)
In the south of Norway, we find Byglandsfjorden, a lake in the municipalities of Evje and Hornes and Bygland in Agder. This is where the bleak live.
The lake is part of the Otra watercourse, which stretches from Vassenden in the south to Ose in the north. Until the 1960s, the bleka was found in large parts of the Otra watercourse. Now it lives mainly in the elongated Byglandsfjorden, which has an area of 40 km2.
Bleka rarely lives more than five or six years and does not grow larger than 30 cm. It has a slender body shape and a long, narrow tail root. It often has only one to three black dots on each gill cover.
In 1926, Professor Dahl, a Norwegian zoologist, described the bleka as "a breathtaking beauty". He was the first person to mention the bleke. Previously thought to be a separate species of fish, the bleke is an Atlantic salmon - just like the migratory salmon.
because it is only found in the Byglandsfjord in southern Norway.
because there are few left. Bleka has little variation in its genetic material and is not very tolerant of changes in the environment in which it lives. Bleka has been isolated for about 9500 years.
because over the past 100 years, we humans have destroyed large parts of the bleak's habitat.
because the bleak is unique. If the bleak disappears, we can't replace it with other salmon.
For the first two to three years of its life, the bleak lives in running water or near the water's edge in Byglandsfjorden. As it grows, it migrates further out into the lake.
Bleka eats mostly zooplankton, such as copepods and copepods.
Like sea migrating salmon, bleak change their appearance when they migrate into the lake. They become silvery and slimmer. Some bleak develop a red edge on their tail fin as the spawning season approaches. No other salmon strains change the color of their tail fin.
Bleka reaches sexual maturity when it is three to four years old. The spawning season is in December, and it is the female fish that selects a suitable spawning ground. Bleka spawns both in the lake and in running water. It buries the roe 3-6 cm into the gravel, where it remains protected until the summer. Only then do the fry emerge from the gravel in search of food. Each female has an average of 248 eggs.
Photo: Bjørn Barlaup, NORCE
Bleka are adapted to a life in freshwater and feed mainly on small zooplankton. It does not have access to as much and varied food as the sea-going salmon find in the sea. Bleka therefore do not grow much larger than 30 cm.
The development of hydropower and acid rain were the two main reasons why the bleak almost became extinct in the late 1960s. A small number of bleak were found and preserved in fish farms. This was the start of a major rescue operation to preserve the bleach.
A fish farm is a kind of factory for producing fish. Here, people ensure that eggs from the female fish and milk from the male fish are mixed so that the eggs are fertilized. The eggs are placed in tanks with clean running water and eventually hatch into fry. Humans monitor the water temperature and conditions in the tanks. This is called hatchery operation.
Since the late 1970s, 2.2 million fry have been released from the fishing facilities at Byglandsfjorden. More recently, fertilized eggs have also been released in suitable spawning areas.
Now bleak spawn naturally in several spawning areas, and fry and eggs are no longer released here.
Picture of the Byglandsfjorden dam. Photo: Anders Martinsen
Acid rain means that pollutants in the air come down to earth along with rain or snow. When it ends up in rivers and lakes, the water becomes more acidic - and toxic to bleach and other species.
During the first half of the 20th century, hydroelectric power was developed in several places in the Otra watercourse. This damaged the environment, and several of the spawning and living areas for the bleak were drained. This led to the death of eggs and fry.
Commercial fishing for trout was carried out in Byglandsfjorden. Fishing was done with large traps, a tool that catches the fish alive. The fishermen also caught bleke, and the stock was reduced. Small squid that could not be used as food fish were released.
The earwig is one of our most common carp fish, but it does not naturally belong in Otravassdraget. How it got there is somewhat uncertain. For example, it may have been used as live bait. The population of earwigs is increasing, and they feed on the same food platter as the bleak. Earwigs often have parasites that can easily infect the bleak.
Several places in the Otra watercourse are limed to counteract the effects of acid rain. Liming improves water quality, increases fish production and creates a richer biodiversity.
To strengthen the bleaching, fish fry have been stocked and fertilized roe has been placed in suitable spawning areas.
There used to be bleke in the river Otra upstream of Byglandsfjorden. Here, fertilized eggs are placed in the old habitats in the hope that the bleak will re-establish themselves.
Bleka needs gravel to bury the roe. New gravel has been added to create new spawning areas and to repair damaged ones.
Rules have been introduced for how the power plants are to be operated. They are not allowed to draw so much water that the spawning and living areas of the octopus are dried up.
Commercial fishing for bleak is no longer allowed. Hobby fishermen can still fish for bleak.
To help the bleka past a stretch of river below Hekni power station, a separate river course has been created. This makes it easier for the bleka to swim upstream when conditions in the main river prevent it. In addition, the bleak run is a new and important spawning and living area.
Liming can be done by boat. Photo: Franzefoss Minerals
