Covariation in year-class strength of perch, Perca fluviatilis L and pikeperch, Stizostedion lucioperca (L)

Covariation in the year-class strengths of perch, Perca fluviatilis L., and pikeperch Stizostedion lucioperca (L.), were studied among ten populations in Baltic coastal areas and three pikeperch populations in lakes. Within the studied periods in 1974-1981 and 1980-1987 the covariations in the year-class strength were similar between populations of the same species and between species. When the variations in year-class strength in several populations were compared annually between species no statistically significant differences were found during the 16 examined years. Despite the covariations, correlation coefficients in year-class strength between populations were lower for greater distances. About half (18 cases out of 35) of the correlation coefficients were statistically significant when the distance between populations was less than 300 km. Some rather high correlation coefficients were also found at distances between 300 and 900 km, but only one was statistically significant.