Fish stock assessment in dam reservoirs located in the upper Vistula and Warta river catchment areas based on angling catch records
Iwona Psuty, Halina Wilkońska
ABSTRACT. Time-series of the species caught in a complex of four fyke nets that were monitored and recorded by a team of volunteer fishers provided the basis for identifying trends in the changes of fish assemblages during the 1995-2006 period. The fish assemblages exhibited strong seasonality with herring, Clupea harengus L. domination during spring. In the summer season, juvenile pikeperch, Sander lucioperca (L.) and ruffe, Gymnocephalus cernuus (L.), were dominant in number. The relative abundance of eel, Anguilla anguilla (L.) exhibited a clearly decreasing trend due to fishery exploitation and the lack of stocking. The decreased share of the largest pikeperch individuals suggested that this species is being overexploited. Ruffe exhibited a strong decline more probably due to strong impact from numerous black cormorants. Increased abundance was observed in the case of roach, Rutilus rutilus (L.), flounder, Platichthys flesus (L.) and round goby, Neogobius melanostomus (Pall.), a new species in ecosystem.
Key words: herring, bream, eel, pikeperch, round goby, ruffe, fyke net
CORRESPONDING AUTHOR:
I. Psuty [+]
Department of Fishery Resources
Sea Fisheries Institute in Gdynia
Kollataja 1, 81-332 Gdynia, Poland
Tel. +48 58 7356218, fax +48 58 7356110
e-mail: iwcia@mir.gdynia.pl
H. Wilkońska
Department of Ichthyology
The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Poland