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METHYLMERCURY BIOACCUMULATION DEPENDENCE ON NORTHERN PIKE AGE AND SIZE IN TWENTY MINNESOTA LAKES
Glass, G E., J. A. Sorensen, AND G. R. Rapp Jr. METHYLMERCURY BIOACCUMULATION DEPENDENCE ON NORTHERN PIKE AGE AND SIZE IN TWENTY MINNESOTA LAKES.
Mercury accumulation in northern pike muscle tissue (fillets) was found to be directly related to fish age and size. Measurements were made on 173 individual northern pike specimens from twenty lakes across Minnesota. Best fit regressions of mercury fillet concentration (wet wt.) vs. length, weight and age were found using power (log-log transforms) as compared with exponential or linear forms. The resulting equations (after averaging the individual equations for the 20 cases) are: ]Hgl], ppb fillet = 0.50(length, cm)2.17 = 7.3(weight, g)0.68 = 110(age,yr)1.00, with r2 = 0.76, 0.72, and 0.76 respectfully. Lengths, weights, and ages ranged over 22-110 cm, 60-7,500 g. and0.3-11 yr., respectively, and [Hg} ranged from 50 to 2,000 ppb. For the purposes of making interlake comparisons, computations of mercury levels for standard length, weight and fish age were made for each of the 20 lakes studies. Age based comparisons were found to correlate with methylmercury concentrations in lake water, and total mercury concentrations in lake plankton. Methyklmercury bioaccumulation factors (BAFs, total mercury in fillets divided by total methylmercury in lake water) ranged from 0.3 - 14 x 10 6 for individual specimans. Methylmercury BAFs showed a similar dependency on fish size and age as [Hg] in fillet, i.e., methylmercury BAFs = 3,030 (length, cm) 2.17 = 47,100 (weight, g) 0.68 = 752,000 (age, yr.) 1.00, where values represent the means of twenty different lake equations. Fish mercury levels indicate that each lake differs in its own characteristics controlling bioaccumulation processes and transport through the aquatic food chain. Assuming no age or size dependency of fish mercury contentrations and BAFs may result in impact overestimates for younger fish and underestimates for older fish from mercury contamination in aquatic ecosystems.