This report is based on experiments carried out in Lake Tegel, Berlin (West) in November 1985 under the auspices of the European Inland Fisheries Advisory Commission (EIFAC).
The plans for the present work were discussed in Aarhus in May 1984, during the 13th session of EIFAC and at a meeting of the Steering Committee in Hamburg on 6 June 1985 by Prof. Dr. Tiews, Dr. Lindem, Dr. Hartmann, Dr. Löffler, Dr. Dahm, Dr. Burczynski, (BioSonics), Dr. Grosch (Fischereiamt Berlin), Mr. Doering, and Mr. Völzke.
The exercise followed the 1980 exercise in Konnevesi (Bagenal et al., 1982), during which the number of fish and the size distribution as assessed by echo sounder were compared with assessments based on trawl catches. It followed also the 1983 exercise in Lake Constance (Dahm et al., 1985), during which the acoustic assessment was compared with that obtained from Virtual Population Analysis determined from commercial catches.
The intention of this exercise was to compare different acoustic methods of pelagic fish stock assessment in a shallow inland water by comparing assessments made by different echo sounders with those based on mark-recapture experiments. Although there exist a large number of papers on acoustic fish population estimating techniques, such a comparison of the results of various acoustic methods with those of a nonacoustic method are rare (Mulligan and Kieser, 1986).
This exercise took place in Lake Tegel, Berlin (West), 52°35' N/ 13°15'E) (Figure 1) from 11 to 15 November 1985.
Lake Tegel is a eutrophic lake, which is linked at its south-western part to the river Havel and separated by small islands. Lake Tegel has a surface area of 4 km2, a mean depth of 6 m, and a maximum depth of 16 m. The experiment was carried out in the main basin within an area of 3 km2 and a depth of 8 m. Total water volume of Lake Tegel is 32 x 106 m3, with a volume of 10.35 x 106 m3 in the part deeper than 5 m (Table 1).
In the North of Lake Tegel there are two draining creeks, the Tegeler Fliess and Nordgraben.
Fifteen oxygen aerators (LIMNO units, Atlas Copco) have been working in the lake to supply oxygen to the hypolimnion (10 m3 / min).
The phosphate elimination plant, Berlin-Tegel, was installed in 1986 with the intention of improving the water quality of the Lake.
Further limnological details are given in Senator für Stadtentwicklung und Umweltschutz (1984), Kloos (1978), Böcker and Sukopp (1985) and Franke (1973).
A commercial fishery in Lake Tegel and in the upper Havel produced a total catch of 72 t in 1985 using seines and two-boat trawls. No data exist on the catches of the 5 000 anglers. The commercial catch corresponds to 100 kg fish/ha/a and includes 84 % coarse fishes (Blicca björkna and Abramis brama). Details of yield and stocking are shown in table 2.
Further details of Lake Tegel's fish population are given in George (1985) and Grosch (1980).
Participants from outside the Federal Republic of Germany were Dr. T. Lindem, Institute of Physics, University of Oslo, Norway; Prof. Dr. P. Tuunainen and Dr. J. Jurvelius, Finnish Game and Fisheries Research Institute, Helsinki and Enonkoski, Finland; Mr. G. Raemhild and Mr. J. Dawson, BioSonics Inc., Seattle, U.S.A.; Mr. F.H. Kristensen, SIMRAD Subsea A/S, Horten, Norway; Dr. J. Vostradovsky, Fishery Research Institute, Reservoir and River Laboratory, Libcice nad Vltavou, CSSR.
German personnel included Dr. E. Dahm from the Institut für Fangtechnik, Bundesforschungsanstalt für Fischerei, Hamburg; Dr. J. Hartmann and Dr. H. Löffler of the Institut für Seenforschung und Fischereiwesen, Langenargen; Mr. P. Doering and Mr. V. Völzke, Freie Universität Berlin; Miss S. Jürgensen and staff of the Fischereiamt Berlin.
Dr. T. Brenner, Landesanstalt für Fischerei Nordrhein-Westfalen, Albaum joined the exercise as an observer.
