Dynamics of the numbers and distribution of juvenile pikeperch in the Szczecin Lagoon and Pomeranian Bay in 1995-1996

Abstract

Seasonal migrations and preliminary assessment of the numbers of pikeperch fry are presented for the Oder River estuary (Szczecin Lagoon and Pomeranian Bay). The data were obtained using the computer programme „Surfer for Windows”. Observations embraced fish generation born in 1995, represented by age groups 0 and 1, and that born in 1996, represented as age group 0, and were carried out in summer and autumn of the two years. Fish numbers differed considerably depending on the generation: 1995 generation was very numerous, so that 1996 one was only 4 % of the 1995. Juveniles of numerous 1995 generation showed strong tendency to migrate to Pomerania Lagoon, while no such trend was observed in the case of 1996 generation. The materials suggest that more numerous generation was born at higher water salinity, while weak generation of 1996 was born at high nitrogen content in water. Also average water temperature in May-June was a little lower in the case of strong generation than of the weak one. Weak generations of 1993 and 1996 resulted in low pikeperch catches and pessimistic outlook as regards pikeperch landings until 1999.