MERCURY IN FISH IN THE SMALLWOOD RESERVOIR, LABRADOR, 21 ONE YEARS AFTER IMPOUNDMENT

The elevated mercury (Hg) levels in fish flesh found after impoundment of a reservoir, are predicted to decline as the reservoir ages. The l ength of time required for a return to background levels is dependent on among other things. the trophic status of the fish. Predictions for omnivorous species range between 15 and 20 years while for piscivorou s species they vary from 20 to 30 years. Fish in the Smallwood Reservo ir, Labrador, Canada were sampled 6 years after impoundment when hg le vels were found to be elevated in most species. Selected of the sites were re-sampled after 16 years and again after 21 years. Mercury in th e flesh of omnivorous species such as lake whitefish (Coregonus clupea formis) had returned to background levels after 16 years as predicted. However, hg in the flesh of piscivores such as northern pike (Esox lu cius) and lake trout (Salvelinus namaycush) remained elevated even 21 years after impoundment. While the levels in lake trout have declined somewhat in that time, there is no evidence of decline in the northern pike either within the reservoir or at downstream stations. Models pr edicting decline in hg levels in piscivorous fish in reservoirs must b e re-evaluated in light of this extended data set.