Analysis of fin clips as a nonlethal method for monitoring mercury in fish

Monitoring of mercury in fish typically involves removal of individuals from the sampled population and subsequent analysis of fillets. This study assessed whether the analysis of fins, structures routinely clipped to mark released fish in population studies, could provide a nonlethal approach for estimating mercury concentrations in axial muscle (fillets). We analyzed fillets and selected fins from 401 northern pike (Esox lucius) and 79 walleye (Sander vitreus) from 21 lakes in Minnesota and Wisconsin, 19 Arctic grayling (Thymallus arcticus) from Toolik Lake, Alaska, and 14 winter flounder (Pseudopleuronectes americanus) from Long Island Sound, New York. On average, 83% of mercury in fins was methylmercury, and concentrations in the proximal portion were about half-those in the distal portion in pelvic fins. Mean concentrations of mercury in fins, averaged by species and fin type, ranged from 2.7 to 8.9% of those in fillets. Coefficients of determination (r2) for linear regressions of mercury concentrations in fillets against those in fins of individual fish ranged from 0.04 to 0.96 among species and water bodies (median r2 = 0.52). The concentration in fin clips was a better predictor of mercury in fillets for individual Arctic grayling (r2 = 0.65, n = 12 and r2 = 0.84, n = 8) and winter flounder (r2 = 0.94, n = 14) than for individual northern pike (median r2 = 0.56) or walleye (median r2 = 0.22) from a given lake. In northern pike in the 400-500 mm total-length interval, the mean concentrations of total mercury in caudal fins and fillets, averaged by lake (n = 12), were strongly correlated (r2 = 0.95). The analysis of composited samples of fin clips from fish within a restricted length interval could, therefore, be a useful screening tool for assessing the relative mercury contamination of fish among different water bodies.