January

Food to be found in the winter river

Is there really any food to be found for the young salmon in winter? The cold river may seem completely lifeless, but even in January the young salmon find food. On the bottom - between and on top of rocks, in the river gravel and buried in the silt - the benthic animals live during the winter. Due to the low water temperature, they are more or less dormant. Many flying insects spend the larval stage in the river. While adult life on the wing can last a few hectic weeks, the larval stage in the river can last two to three years. This means that the young salmon have food all year round. The largest juvenile salmon eat a lot of caddisfly, stonefly and mayfly larvae. For the smallest, feather mosquito larvae are important food.

After around 100 years of power development, a third of our salmon rivers are now affected by river regulation. Regulation can lead to changes in ice formation, temperature, water flow and water quality. This affects life in the river and can have negative consequences for both salmon and benthic animals. For example, regulation can make the river warmer in winter, when warmer water is drained from the bottom of the reservoirs. This can cause salmon eggs to develop faster than normal, resulting in premature hatching. As a result, the salmon fry may emerge from the gravel at an unfortunate time in terms of flooding, temperature or the presence of benthic animals.

An ice-covered river is the best thing for young salmon. The ice acts as a protective cover that provides stable conditions, less visibility and less stress. Under such conditions, half or more of the fry that survive the first summer will also survive the winter.