MERCURY ACCUMULATION AND BIOMAGNIFICATION IN OSPREYS (PANDION HALIAETUS) IN THE JAMES BAY AND HUDSON-BAY REGIONS OF QUEBEC

Mercury exposure was examined in adults and nestlings of ospreys (Pand ion haliaetus) from lakes, rivers, and hydroelectric reservoirs in nor thern Quebec between 1989 and 1991 by assessing the amount of mercury transferred from fish to ospreys, which are voracious fish-eaters. The high mercury concentrations detected in adult feathers and tissues (f eathers, blood, liver, kidneys, muscles, brain) of nestlings indicate an increase in mercury availability at recently constructed hydroelect ric reservoirs (10-12 years for the La Grande-2 Reservoir). With mean total mercury levels of 37.3 mg/kg and 1.9 mg/kg in feathers (dry weig ht) and in blood (wet weight), respectively, contamination rates were, in both tissues, five times higher for chicks born near the La Grande Reservoirs (western sector) than in those oared in natural habitats. Furthermore, the mean quantity of total mercury in 40-day-old chicks r eared near a reservoir was 10.5 mg, compared with to 1.6 mg for those reared in a natural environment. Modeling of mercury transfer from fis h to osprey nestlings showed that the mercury level in chicks' blood p rovides a good estimate of mercury concentrations in ingested food. In addition, the relationship between mercury concentrations in the bloo d and that in feathers indicates that substantial biomagnification of mercury occurs from the ingested dose to the feathers. The intensity o f this biomagnification varies with the age of the chicks and reaches a maximum value as the flight feathers start to form (at 20-25 days of age) declining thereafter until the bird is 45 days old and growth of those feathers is complete. Nevertheless, the mean number of young fl edged on reservoirs where mercury exposure is greatest (>40 mg/kg of H g in chicks' feathers) did not differ (1.6 +/- 0.7) from that observed elsewhere in built-up environments (1.9 +/- 0.7) or in natural habita ts (2.0 +/- 0.7) (H = 4.39; p = 0.11). Storage of mercury in growing f eathers (86% of all mercury in osprey) prevents accumulation in living tissues, thereby protecting the chick from related toxic effects. How ever, toxicological problems may arise after fledging. In particular, attention should be paid to postfledging survival before concluding th at mercury exposure is insufficiently high in Osprey young reared at r eservoirs.