Winter fish kills are observed as a result of both a complete cessation of oxygen supply from the air and a sharp restriction of plant life under the ice. The formation of a solid ice cover and the inability of water to contact air is the main factor that can cause fish kills.
Winter fish kills occur within each individual water body not everywhere, but in separate areas, the size of which varies from year to year. Depending on the duration and stability of the ice cover, water reserves, and fish stocking density, in some winters fish die completely, while in others only individuals most sensitive to oxygen deficiency perish. Sharp fluctuations in water level can cause great harm to overwintering fish, resulting in fish being crushed by ice in the coastal zone of the water body, leading to their death.
The first signs of winter fish kills are the appearance of juvenile fish in ice holes and openings. The water at this time acquires an unpleasant odour and becomes turbid.
In accordance with the Law of the Republic of Belarus "On Wildlife", state bodies, other organisations, and citizens are obliged to take measures to protect wild animals and fish found in emergency situations.
Lessees and users of fishing grounds (in leased fishing grounds or those granted for gratuitous use) and local executive and administrative bodies (in fishing grounds of the reserve fund) are responsible for organising and carrying out measures to prevent fish kill phenomena in accordance with the Rules for Fishery Management and Fishing.
Amateur anglers who visit water bodies should also not remain indifferent. They can help overwintering fish by making ice holes, thereby "introducing" additional oxygen into the water.
What measures should be taken to prevent mass fish deaths during the winter period?
Firstly, timely ice holes should be made in water bodies. Their number depends on the area of the water body and averages 3-5 per hectare. Ice holes are made both in the centre of the water body and along its perimeter, where the depth of the unfrozen layer is 50-60 cm. To prevent ice holes from freezing over, it is necessary to install bundles of reeds, cattails, and other hollow "breathing" plants in them and hang bags of salt.
Secondly, to apply lime to water bodies. Liming promotes the decomposition and accelerated mineralization of organic matter, as well as improves the gas regime and neutralizes the acidic reaction of water. Unslaked lime is applied at a rate of 1-2 centners per hectare; when using slaked lime or ground limestone, the application rates increase by 1.3 and 1.8 times, respectively.
Thirdly, to suspend bags with salt in such ice-holes at a rate of 5 kg per bag. Technical salt, which is used for cleaning boilers in boiler houses, can also be recommended as salt.
The Lepel Inter-district Inspectorate for the Protection of Fauna and Flora requests everyone who visits water bodies to report to the Lepel Inter-district Inspectorate for the Protection of Fauna and Flora at the phone number 8 (02132) 3-43-85 upon the first signs of winter fish kill, or to take the above-mentioned measures independently to save the fish.