Spatial heterogeneity of mercury bioaccumulation by walleye (Stizostedion vitreum) in Lake Roosevelt, Washington

Mercury bioaccumulation was examined in muscle tissue of walleye (Stizostedion vitreum) from Lake Roosevelt, a large (80,000 acres) reservoir receiving metal contaminated wastes from mining and associated processing activities. Walleye were collected from three spatially segregated reaches distributed along the relatively narrow axis of the reservoir to investigate whether regional differences in mercury bioaccumulation could be predicted by spatial patterns of mercury in bed sediment. Mercury concentrations in surficial sediments ranged from < 0.05 to 2.70 mg/kg, and generally decreased from the upper to lower reaches in an incremental fashion. Mercury in bed sediments was positively correlated with sediment organic carbon content; however, differences in organic carbon content accounted for only 15 percent of the variability observed in sediment mercury concentrations among reaches. Overall, mercury concentrations in muscle tissue ranged from 0.11 to 0.44 mg/kg wet weight and was positively correlated with age, weight, and length of walleye. Mercury concentrations of walleye varied spatially within the reservoir, with the highest concentrations occurring in fish from the lower and middle reaches. Condition factor (k) of fish was inversely related to tissue mercury concentration, and was significantly lower in fish collected from the lower and middle reaches compared with fish in themore » upper reach. Spatial patterns in mercury bioaccumulation could not be predicted by regional differences in sediment concentrations of total mercury. It is suggested that observed spatial patterns of mercury bioaccumulation may be related in part to preferential utilization of specific regions for spawning and foraging, and that these areas likely differ in mercury bioavailability, owing to local differences in edaphic conditions, and in the kinds and availability of food resources.« less