Abstract

<jats:p> Lake trout, Salvelinus namaycush, released into Tadenac Lake as juveniles, show a pronounced acceleration in growth rate, following a change in diet from benthic invertebrates to rainbow smelt, Osmerus mordax, beginning at age 6 (&gt; 30 cm). An abrupt increase in the rate of mercury accumulation in white muscle of these fish occurs at the same time. Mercury levels in lake trout ([Formula: see text] = 0.24–3.44 μg/g) and coresident smelt ([Formula: see text] = 0.06–0.48 μg/g) from Tadenac and eight neighboring lakes reveal maximum levels reaching 10.0 and 0.84 μg/g, respectively. Mercury levels in lake trout from Tadenac Lake, an undisturbed PreCambrian Shield ecosystem without detected indigenous sources, exceed the "safe" level (0.5 μg/g) at sexual maturity and at a size less than generally acceptable for human utilization. Mercury accumulation by the trout is correlated with length (r = 0.92) in each lake population examined, but substantial among-lake differences occur in fish of comparable ages. As the growth rates are similar in various waters, differences in extent of mercury accumulation is attributed to differences in mercury availability among lakes. In view of a strong correlation (r = 0.96) between mercury levels in smelt and trout calculated at standardized length, it is proposed that the smelt is an appropriate indicator species for the ranking of cold-water lakes relative to the availability of mercury for uptake by lake trout and other living aquatic organisms.Key words: mercury uptake, lake trout, rainbow smelt, growth rate, diet </jats:p>