This report is based on a series of experiments carried out in Konnevesi, Finland, in 1980 under the auspices of the European Inland Fisheries Advisory Commission (EIFAC). It was intended that the experiments would test the precision and accuracy of acoustic methods of pelagic fish stock assessment, by comparing assessments made by an echo-sounder with those based on trawl catches. The assessments were to be of the number of fish and their size distribution. The numbers were to be estimated from capture-mark-recapture experiments and the size distributions from measurements of the trawl catches. Although the capture-mark-recapture estimates of population size were unsatisfactory, comparisons could be made from the volume filtered by the trawl. The comparison of size distributions could be carried out as planned.
The exercise followed on from the Intercalibration Exercise carried out in Finland in 1976 (Bagenal, 1979) in which seven different conventional fishing gears were found too unsatisfactory for stock assessment on account of the great variability in the catches. At its tenth session in Hamburg, EIFAC decided that these experiments should be continued (Recommendation 78/3).
The original plans for the present work were drawn up by a preparatory group which met in Hamburg on 23–24 January 1979. The group consisted of Prof. Dr K. Tiews (Chairman) of the Institut für Küsten und Binnenfischerie, Federal Republic of Germany; Dr T.B. Bagenal (Rapporteur) of the Freshwater Biological Association, the United Kingdom; Dr E. Dahm of the Institut für Fangtechnik, Federal Republic of Germany; Dr J. Kapetsky, FAO Secretariat, Rome, Italy; Dr T. Lindem of the Institute of Physics, Oslo, Norway; Mr R. Mitson, Ministry of Agriculture, Fisheries and Food, Lowestoft, the United Kingdom, and Dr P. Tuunainen. Finnish Game and Fisheries Research Institute, Helsinki, Finland.
Further details were discussed at a meeting in Stavanger on 31 May 1980 during the eleventh session of EIFAC.
The exercise took place at Konnevesi, Finland (Figure 1), from 1 to 10 September 1980. Konnevesi is a lake of 188 km2 divided into two parts by two islands. Northern Konnevesi (68.51 km2) has mean depth of 7.5 m and max depth of 44 m, while southern Konnevesi is 119.45 km2 and has a mean depth of 12.5 m and a max depth of 56 m. The largest channel between north and south parts of the lake is 80 m wide and 13 m deep, and the other two channels are 5 m and 10 m wide and about 4 m deep. Papers describing the chemical and physical hydrography, phytoplankton, zooplankton as food for vendace, bottom fauna and fish fauna were published in Suomen Kalatalous, Volume 46, pages 1–44, 1972.
The work was concentrated on an area in north Konnevesi marked on Figure 2. The depth in the area reaches 44 m and echo-grams of a north-south traverse is shown in Figure 3.
From outside Finland, the people taking part in the exercise were Dr E. Dahm, Mr E. Möthe and Mr A. Schulz from the Institut für Fangtechnik, Hamburg; Mr H. Löffler of the Institut für Seenforschung und Fischereiwesen; Dr Torfinn Lindem from the Institute of Physics, the University of Oslo; and Dr T.B. Bagenal from the Freshwater Biological Association, Windermere Laboratory. The Finnish personnel consisted of Dr P. Tuunainen and staff of the Fishery Division of the Finnish Game and Fishery Research Institute, Helsinki. Much of the success of the exercise depended on the day-to-day arrangements and excellent organization of Mr Juha Jurvelius.
