HYDROACOUSTIC MONITORING OF VENDACE IN SELECTED MAZURIAN LAKES
Lech Doroszczyk, Bronisław Długoszewski, Ewa Kanigowska, Małgorzata Godlewska
The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Poland
ABSTRACT. Hydroacoustic monitoring (SIMRAD EY 500 split beam echosounder, 120 kHz) was performed in four coregonid lakes in which commercial catches of vendace, Coregonus albula (L.) decreased dramatically over the last decade. It has been shown that in two of the lakes the hypolimnion, which is the natural habitat of vendace, is devoid of fish. In another the fish is abundant, but its body size is too small to be caught. In yet another there is a healthy population of vendace, but the abundance of cyprinid fishes is ten fold higher than that of vendace. The competition for food probably limits natural reproduction, and thus the biomass of adult vendace. Oxygen deficits in deeper layers, especially during fall, are responsible for the disappearance of the fish from the lakes.
Key words: VENDACE, HYDROACOUSTICS, FISH BIOMASS, LAKE QUALITY
CORRESPONDING AUTHOR:
Małgorzata Godlewska, Instytut Rybactwa Śródlądowego, Zakład Rybactwa Rzecznego, ul. Główna 48, Żabieniec, 05-500 Piaseczno, Tel./Fax: +48 (22) 7562044; +48 (22) 7562088; e-mail: margogod@wp.pl