| Summary: | Lake Vortsjärv is a large (area 270 km2), shallow (maximum depth 6.0 m) and turbid eutrophic lake in which eel Anguilla anguilla (L.), pikeperch Sander lucioperca (L.), northern pike Esox lucius L. and bream Abramis brama (L.) are the main commercial fishes.High water level of the lake has a strong positive influence on the abundance and total catches of fish. Constant low water level and severe winters cause hypoxia and consequent fish kills.The present investigation shows that the CPUE decreases rapidly when the oxygen 1 m below the ice falls to below 4 mg O2 dm3. In winter, eel moves out of the bottom mud before the oxygen level falls below 0.3 mg O2 dm3 near the bottom. It either emigrates from the lake or else can be easily preyed upon by pike. Due to the extremely low water level in 1996-1997, the southern end of L. Vortsjärv was full of macrophytes. Therefore, the normal migration and spawning of pikeperch, which prefers open water, was seriously hindered. JRC.H.5 - Rural, water and ecosystem resources
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