| Abstract [eng] |
The population of Atlantic salmon (Salmo salar L.) and Sea trout (Salmo trutta trutta L.) in Lithuania used to be much bigger. But by the beginning of this century due to the increased water pollution and dam construction improvement stocks of these species almost reached the level of extinction. That is why some measures where taken to save the population. In 2005 fish ladder was built in Siesartis river providing fish access to extra 25 km of the rivers respectively. In Siesartis River distribution of redds bellow and above dam varied significantly over monitoring area. The biggest increase of redds above dam was in 2007-2008, 2-3 years after fish ladders construction.. In 2008 relative abundance of redds above the dam was significantly greater than bellow the dam and mean values of relative redds abundance, area and mean size over all monitoring period were also greater for river stretch above the dam. From radio tagged 18 salmonid specimens in Siesartis river 13 (10 females and 3 males) were registered very close (<50 m) to fish ladder. Of those registered 9 fishes ascended fish ladders and 6 of them passage. Movement analysis through fish ladders revealed that most time fishes spent in the middle of fish ladders. Fish ladders passage time did not depend on sex neither on fish size (Mann-Whitney U test p>0.05). Radio tracking studies revealed that Valtūnai hydropower plant fish ladders efficiency was 66 % - two thirds of salmonids ascending fish ladders actually passed it. |
