Juha Jurvelius

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All sampling methods give selective or biased estimates of fish species abundance, distribution and size structure. This creates problems, e.g. in regard to the Water Framework Directive of the European Union, which demands evaluation of the quality and status of fish stocks in lakes. We compared fish sampling by means of Nordic multimesh gillnets, seining,(More)
Short-term streamflow regulation (hydropeaking) affects the ecology of regulated rivers. We examined the longitudinal and temporal changes occurring in fish assemblages in a hydropeaking single river reservoir between two power plants by using electrofishing along the shoreline, hydroacoustics and test fishing in the open water. A longitudinally changing(More)
A large scale biomanipulation of pelagic fish by trawling was started in the eutrophic Enonselkä basin (26 km2) of Lake Vesijärvi to improve the water quality which had remained poor in spite of the termination of nutrient loading. The distribution and density of the fish were studied by hydroacoustics before and during the removal. The initial annual fish(More)
To evaluate the consistency of mobile and vertical echosounding results from the 1980s to the 2000s, fish density (fish ha−1) and target strength (TS, dB) estimates of single (70 and 200 kHz) and split (38 and 120 kHz) beam echo sounders were compared under varying light conditions. Acoustic estimates were compared with trawling results. During daytime(More)
The post-war fishery of Lake Ladoga can be divided according to its catch level into four periods. In the years 1945–1954 the total annual catch increased, and reached the level of 4000 tonnes. In this period the fish stocks that had increased during the war years were intensively exploited. However, this fishery was not in balance with the stocks during(More)
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