| Abstract [eng] |
Researches on salmon (Salmo salar L.) adults and juveniles are important for the estimation of these fish stocks. The growth of individuals varies temporarily and spatially, relatively to abiotic and biotic factors. The aim of this work is to estimate a peculiarity and density of salmon population and define ecological conditions - dependent growth of salmon juveniles in Lithuanian rivers. Investigations were carried out in different salmon rivers sampling stations in 2000 – 2006, in pursuance of programme of salmon fish abundance monitoring in investigated water bodies by Institute of Ecology of Vilnius University, and in pursuance of programme of releasing cultured salmon juveniles into rivers by Lithuanian State Pisciculture and Fishery Research Centrum. Data for the overview of Žeimena, Vilnia and Šventoji river‘s hidrological regime was collected from Lithuanian Hydrometeorological Service under the Ministry of Environment for year 2000 – 2006. In 1999 – 2006 about 715560 individuals of cultured salmonids were released at all life stages, i.e. as fry, juveniles and smolts. 39 % of it‘s hatchery production comes for Neris river basin, 34 % - Šventoji river basin, 11 % – Šventoji (seabord) river basin, 10 % – Dubysa and 6 % Minija river basin. According to research and experimental assessment potential salmon smolt production in Lithuanian rivers amounts to 137 000 individuals. However, the actual annual wild salmon smolt production makes only 25.6 – 26 % of that potential. Most of the salmon smolt production has been recorded in Žeimena, Šventoji, Vilnia and Siesartis rivers. Estimating the ecological condition of Žeimena, Vilnia and Šventoji rivers has been recorded light changes since 2002: rised temperatures, water level and stream flow. Studies proved, that better abiotic conditions for salmon are in Šventoji river, where water temperature, water discharge are higher and water level lower. Biological indices of juveniles both parr 0+ both 1+ smolt in this river are higher: 0+ age individuals L=11,26 cm, l=9,89 cm, Q=13,85 g; 1+ age individuals - L=11,78 cm, l=10,37 cm, Q=32,81 g. Accomplished studies presented that, hidrological regimes parameters, especially water level, influence 0+ age indivuduals than 1+ age individuals. Elder salmon juveniles (1+) are mostly affected by dissolved oxygen concentration. The results show a significant dependence of Vilnia river ecological condition on salmon individual growth of parrs (rL=0,90; rl=0,90; rQ=0,84; p<0,05). A significantly negative correlation was determined between biological indeces of 1+ age indivuduals of Žeimena river and dissolved oxygen concentration (rL=-0,89; rl=-0,89; rQ=-0,90; p<0,05). |
