A multi-level biological approach to evaluate impacts of a major municipal effluent in wild St. Lawrence River yellow perch ( Perca flavescens )

Mercury (Hg) contamination of the St. Lawrence River along the Cornwall waterfront is the result of over a century of industrial inputs. Yellow perch (Perca flavescens) are contaminated above the consumption guidelines deemed safe by Health Canada in one of three contaminated depositional zones. Amphipods are crustaceans that play an important role in aquatic food webs, and a recent study of the diet of yellow perch showed that amphipods were the primary food source of yellow perch in these zones and that amphipods showed similar patterns of Hg contamination. However, not all Hg taken up by amphipods is bioavailable. That is, not all Hg is incorporated into the tissues and available for uptake by yellow perch. To determine if Hg analyses of amphipods are biased by Hg present in their gut contents, the rate of Hg loss was measured from the gut and tissues. Amphipods were collected in the field using artificial substrates. A sample was frozen immediately upon retrieval, and the remaining amphipods were kept in a sieve in a basin of filtered river water. Amphipods were then sampled over 16 days to compare Hg concentrations in gut contents and tissues before and after they were removed from the Hg source in the field. The data were used to estimate the portion of Hg bioavailable to yellow perch. This enables us to more accurately estimate the extent of Hg contamination that is moving through the Cornwall food web, leading to elevated concentrations in top trophic fish species.

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Contaminant levels in St. Lawrence River yellow perch (Perca flavescens): spatial variation and implications for monitoring

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f97-198 ◽

1997 ◽

Vol 54 (12) ◽

pp. 2930-2946 ◽

Cited By ~ 14

Author(s):

J Ion ◽

Y de Lafontaine ◽

P Dumont ◽

L Lapierre

Keyword(s):

Trace Metal ◽

Yellow Perch ◽

Power Level ◽

Perca Flavescens ◽

Bioaccumulation Factor ◽

Maximum Difference ◽

Pcb Congeners ◽

Spatial Differences ◽

Power Analyses ◽

St Lawrence River

Yellow perch (Perca flavescens) (n = 50) were collected from five geographic sectors between 1991 and 1992 to assess the spatial variability in trace metal and PCB (10 congeners) levels along the St. Lawrence River. Spatial differences among the five sectors were analyzed using two-way ANOVA and were significant only for PCBs. Both Hg and total congener concentrations were significantly and positively correlated with fish age, but not with mass or length. The relative proportions of the PCB congeners did not vary among sites. The bioaccumulation factor (BAF) of 3700 for total congeners compared favourably with previously reported results. Since 1975, Hg and PCB levels in St. Lawrence River yellow perch have decreased by factors of 2-3 and 30, respectively. Power analyses revealed that future monitoring studies may require large sample sizes to successfully detect the small spatial differences found for many contaminants. For example, to detect, at a power level of 90%, a 33% difference in Hg levels in yellow perch (i.e., the maximum difference found in this study) among the five sectors, 80 fish per sector would be required.

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