Opinion|Reader’s opinion
The number of trout rising into the river can easily be increased by deepening and widening the neck of the side channel, so that a larger part of the total flow is directed to the side branch.
Discourse The demolition of the Old Town Dam has been very emotional and political. It is therefore worth bringing to the debate the facts about the reproductive biology of salmon and trout.
First of all, Vantaa is not a salmon river but a rising fish is a sea trout. The species affects the uplift of fish in the river. Salmon rises begin around the spring flood and continue until spawning time in October. Some sea trout rise in late winter and early spring and continue to rise until autumn. In addition, some sea trout remain in the river and participate in spawning with fish rising from the sea.
The area of the juvenile production areas, ie the rapids, determines how much the river can produce juveniles migrating to the sea and thus also the fish returning to the river. The chicks take over the territory from the rapids and defend it. Therefore, the addition of fish can only increase juvenile production if the number of spawning fish is not sufficient to fill the rapids in the juveniles. Over the past five years, chick production has been about 80 percent of production capacity.
The number of trout rising into the river can easily be increased by deepening and widening the neck of the side channel, so that a larger part of the total flow is directed to the side branch. The fishing road in the side channel is being improved and the ascent itself is being facilitated. These measures alone should be sufficient to provide enough spawning fish to fill the rapids in the juveniles. In normal years, the dam is dry for part of the year, so mother trout can always go up to Vantaa.
Vantaa can be improved as a trout river by improving spawning grounds and increasing gravel-rich spawning grounds and improving water quality so that roe does not suffocate due to gravel siltation. In addition, trout fishing in the sea can be restricted. However, the most important thing is to remove the last obstacles to hiking in Vantaa, as it would increase the number of chicks by more than a quarter.
Improving the seedling stock in Vantaa should focus on these measures and stop hate speech about the demolition of the protected dam in Vanhankaupunginkoski.
Olli Sumari
fish biologist, former director of the State Central Fish Farm, Helsinki
The reader’s opinions are the speeches written by HS’s readers, selected and delivered by HS’s editorial staff. You can leave a comment or read the principles of writing at www.hs.fi/kirjtamielipidekirjoitus/.
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