CONTAMINANT LEVELS IN ST. LAWRENCE RIVER YELLOW PERCH (PERCA-FLAVESCENS) - SPATIAL VARIATION AND IMPLICATIONS FOR MONITORING

Yellow perch (Perca flavescens) (n = 50) were collected from five geog raphic sectors between 1991 and 1992 to assess the spatial variability in trace metal and PCB (10 congeners) levels along the SC. Lawrence R iver. Spatial differences among the five sectors were analyzed using t wo-way ANOVA and were significant only for PCBs. Both Hg and total con gener concentrations were significantly and positively correlated with fish age, but not with mass or length. The relative proportions of th e PCB congeners did not vary among sites. The bioaccumulation factor ( BAF) of 3700 for total congeners compared favourably with previously r eported results. Since 1975, Hg and PCB levels in St. Lawrence River y ellow perch have decreased by factors of 2-3 and 30, respectively. Pow er analyses revealed that future monitoring studies may require large sample sizes to successfully detect the small spatial differences foun d for many contaminants. For example, to detect, at a power level of 9 0%, a 33% difference in Hg levels in yellow perch (i.e., the maximum d ifference found in this study) among the five sectors, 80 fish per sec tor would be required.