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Diurnal and seasonal fish horizontal migrations in the Sulejów reservoir, Poland

Wojtalik J., Godlewska M., Frankiewicz P., Zalewski M.

Hydroacoustics

2006

Vol. 9

217-226

Horizontal fish migrations in the Sulejów reservoir were studied acoustically. The SIMRAD EY500 echo sounder was used with transducer looking horizontally at three sites of the reservoir located along its longitudinal axis. Fish began to migrate horizontally in June and stopped in October. The diurnal cycle was very well pronounced, with fish going to open water at night and coming back to littoral in early morning. The timing of migrations was correlated with light conditions; the longer were nights the longer fish stayed off shore. Starting from August, apart from diurnal migrations between pelagial and littoral also some movement of fish towards the upper part of the reservoir was noted. It has been hypothesised that it was caused by unfavourable environmental conditions in the lower part of the reservoir, where the Microicystis aeruginosa bloom was observed, and the oxygen concentrations were much lower than in the upper part. These observations confirm that acoustics provides a good tool for controlling behaviour of fish, that are essential indicators of the water quality.

Pattern of spatial fish distribution in the sulejow reservoir monitored by horizontally beaming echosounder and by gill netting

Frankiewicz P., Świerzowski A.

Hydroacoustics

2004

Vol. 7

37-45

The Sulejów reservoir situated on the Pilica River in Central Poland serves as an important source of drinking water for the Lodz Agglomeration. Precise knowledge on fish abundance, community structure as well as spatial and temporal changeability is crucial for proper fishery management (biomanipulation) in order to slow down the reservoir eutrophication and prevent toxic algal blooms. As the reservoir is very shallow (average depth is 3.3 m) it was necessary for fish distribution monitoring to apply, first time in Poland, horizontally looking split beam echosounder (Simrad EY-500 with elliptic transducer ES 120-4x10). Simultaneously, to collect fish for verification of acoustic data and determination of fish species composition, multimesh gill nets were used in representative parts of the reservoir. Prepared maps showing both spatial fish distribution and their density suggest that used methods were suitable for identification of specific areas characterized by different quality of environmental conditions.