THE INCREASE OF COINCIDENCE IN RELATIVE YEAR-CLASS STRENGTHS OF COASTAL PERCH (PERCAFLUVIATILIS L) STOCKS IN THE BALTIC SEA

The year-class strengths of four perch populations (Perca fluviatilis L.) in the Northern Quark of the Baltic Sea were compared using a rela tive year-class strength index. As a result of this it was found that, of the four coastal populations, the three that were reproducing in r ivers or estuaries tended to have coinciding year-class fluctuations. Concerning the river and estuary spawning populations, it was discover ed that acidification overrules the temperature conditions normally af fecting the year-class formation of perch. In the estuaries of the Nor thern Quark the year-class strengths were more extreme and diverged fr om the general pattern in the Baltic Sea. In recent years of less acid ified conditions, the year-class strength of estuarine perch correspon ded more closely to the general pattern in the Baltic Sea.