YEAR-CLASS FLUCTUATIONS OF PERCH (PERCAFLUVIATILIS) IN LAKE PYHAJARVI, SOUTHWEST FINLAND

Year-class variation of perch (Perca fluviatilis), a potentially impor tant predator of larval and juvenile vendace (Coregonus albula), was a ssessed in Lake Pyhajarvi, based on a two-stage sampling of the winter seine net catches in 1989-1995. From these data, we could estimate re lative abundances of perch year-classes for the years 1986-1993. Durin g this period, the year-classes of 1988 and possibly 1992 were strong. The year-class 1988 dominated numerically in catches from 1990 to 199 3 and the year-class 1992 in 1994 and 1995. Year-class strength of per ch was positively associated with the June-August temperature sum.