Mercury Uptake by Lake Trout, Salvelinus namaycush, Relative to Age, Growth, and Diet in Tadenac Lake with Comparative Data from Other PreCambrian Shield Lakes

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Abstract
Lake trout, S. namaycush, released into Tadenac Lake as juveniles, showed a pronounced acceleration in growth rate, following a change in diet from benthic invertebrates to rainbow smelt, Osmerus mordax, beginning at age 6yr (> 30 cm). An abrupt increase in the rate of Hg accumulation in white muscle of these fish occurred at the same time. Hg levels in lake trout (.hivin.x [mean] = 0.24-3.44 .mu.g/g) and coresident smelt (.hivin.x [mean] = 0.006-0.48 .mu.g/g) from Tadenac and 8 neighboring lakes revealed maximum levels reaching 10.0 and 0.84 .mu.g/g, respectively. Hg levels in lake trout from Tadenac Lake, an undisturbed PreCambrian Shield ecosystem without detected indigenous sources, exceeded the safe level (0.5 .mu./g) at sexual maturity and at size less than generally acceptable for human utilization. Hg accumulation by the trout was correlated with length (r = 0.92) in each lake population examined, but substantial among-lake differences occurred in fish of comparable ages. As the growth rates were similar in various waters, differences in extent of Hg accumulation was attributed to differences in Hg availability among lakes. In view of a strong correlation (r = 0.96) between Hg levels in smelt and trout calculated at standardized length, it was proposed that the smelt was an appropriate indicator species for the ranking of cold-water lakes relative to the availability of Hg for uptake lake trout and other living aquatic organisms.