Suomussalmi’s mussel destruction|Raakku also helps other species to get stronger. It needs salmon or trout to reproduce.
Suomussalmi the destroyed river pearl mussel lives in only about 120–150 rivers in Finland. More than 90 percent of them are located in North Ostrobothnia and Lapland, according to the 2022 update by the Finnish Environment Agency (Syke) about species presentation.
In recent decades, the species has only been able to reproduce in 48 rivers, and even in most of them the level of reproduction is not sufficient to maintain the population, states the biologist published in 2015 Panu Oulasvirtan doing in the report.
The exact number of raakkujoki is not known, because not all rivers and streams have been examined to see if they have raakkujoki. Raakku lives only in flowing water, i.e. rivers and streams. It does not live in a lake, for example.
The populations of the river pearl mussel have declined strongly in all areas where it occurs in Finland, even though it was pacified as early as 1955.
Breeding has stopped in the majority of rivers
Especially in the southern rivers, the natural reproduction of the bream has stopped. Crayfish can stay in the river for a long time, even if they do not reproduce, because it is a very long-lived species.
Ministry of the Environment brochure according to the rakku can live to be over 200 years old. Metsähallitus according to today’s majority of the raw in almost all raw deposits are old individuals.
The roach reproduces by parasitizing the fish
The reproduction process of the wrasse is multi-stage, and it requires not only male and female wrasse but also just the right kind of fish population.
The raccoon becomes sexually mature at around 15–20 years of age and reproduces once a year in August–September, according to the ely center’s raccoon protection project in the publication.
Reproduction begins when the raw male drops sperm into the water. After they travel with the water to the female’s gill cavity, they fertilize the eggs. When the eggs have developed into small larvae in the fall, the female places them in the water.
The development of the larvae can only continue if they manage to find a suitable host fish and attach to its gills. Only salmon or trout are suitable as fish, as other fish species are immune to the larvae. Even salmon or trout may have to be of a certain age, as it is possible that even these fish develop immunity with age.
During the winter, the raw larvae that live in the gills of the fish undergo a metamorphosis, after which they detach and fall to the bottom of the river or stream as small clams. If the landing site happens to be suitable, the mussel lives hidden in the gravel for several years, until they appear as shells measuring a centimeter or two, says Metsähallitus.
A full-sized raw is usually about 10-12 centimeters long.
The key species cleans the water
The river pearl mussel takes food from the water by filtering about 50 liters of water per day. Filtration cleans the water.
A single filter still does not clean an entire river, but if there are, for example, a hundred thousand filters in the river, they filter a total of about five million liters of water per day.
Due to the water purification activity, the existence of the raw also improves the living conditions of other species living in the same water. That’s why it’s called a key species.
Raakku is also a so-called top indicator, i.e. an exemplifier species. A vigorous roach population indicates that the water is in good condition. The water has to be in good condition for the raw to be viable.
Before, the threat was pearl fishing
As the name suggests, the river pearl mussel produces pearls, just like an oyster, for example.
Rakui have almost no other enemy species than humans, who threatened the raku populations already at the beginning of the 20th century, when pearl fishing was practiced. According to biologist Panu Oulasvirta’s report, hundreds of clams had to be killed to find a pearl, and up to ten thousand to find a champion pearl.
Finding a high-quality pearl could mean wealth for the pearl hunter. The value of the top pearls could be as much as one hundred thousand euros in today’s money, according to the 2006 publication of the Pohjoisten virtorto raakut mapping project in the publication.
Pearl fishing, which has been practiced for hundreds of years, was very effective in 1955, when legal pearl fishing was put to rest. At that time, for example, compressed air devices were in use, which made diving easier.
Today, the biggest threat to wild animals is the deterioration of habitats.
Traditionally, it has been thought that the mussel forms a bead around a grain of sand or other impurity that has entered the mussel. According to current knowledge however, the pearl is formed in molluscs as a result of tissue damage, and does not require grains of sand or other foreign objects.
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