Piotr Margońskii
Sea Fisheries Institute, Kołłątaja 1, 81-332 Gdynia, Poland

Key words: smelt, larvae, juveniles, spatial distribution, wind velocity, wind direction, seiche, Vistula Lagoon.

Abstract.
The potential impact of meteorological and hydrological parameters on the distribution of zooplankton and smelt larvae and juveniles in the Polish part of the Vistula Lagoon was analysed at 15 stations during four subsequent cruises with different distribution patterns (17-18 June, 1-2 July, 15-16 July, 29-30 July 1998). The results of larvae distribution analysis were compared with rotifer abundance and biomass data obtained from 5 main stations.
Meteorological data (10 minutes of mean wind velocity, wind gust and momentary values of wind direction) were collected in Tolkmicko Harbour about 15 meters above sea level using an automatic weather station. The water current was measured using S4 Current Meters at two locations: at the Russian-Polish border and in the western region of the Polish part of the Vistula Lagoon.
The spatial distribution pattern of zooplankton and smelt larvae and juveniles was influenced mainly by the direction and velocity of winds and by the movement of large water masses. During calm weather (low wind velocity and variable wind direction) smelt gathered in the central part of the investigated area. Gentle winds blowing in a stable direction several days prior to sampling pushed the zooplankton and smelt larvae to the opposite site of the lagoon. Strong winds especially caused juvenile fish to seek calm and shallow waters at the side from which the wind was blowing. The movement of large water masses along the lagoon significantly affected the horizontal distribution of zooplankton and smelt juveniles by dragging or pushing them from one site to another.