A COMPARISON OF MERCURY BIOACCUMULATION IN THREE SPECIES OF FISH FROM COOKS POND, MADISON, NEW HAMPSHIRE AND AVERY BROOK, WEST WHATELY, MASSACHUSETTS

While fish provide necessary omega-3 fatty acids and protein, bioaccumulation of methylmercury (MeHg) in fish poses a threat to human health. Anthropogenic sources (eg. coal burning power plants) have led to an increase in mercury deposition in the northeastern United States and increased MeHg concentration in biota. Yellow perch (Perca flavescens) and chain pickerel (Esox niger) from Cooks Pond in New Hampshire, and brook trout (Salvelinus fontinalis) from Avery Brook in Massachusetts were analyzed for Total Hg (THg) by Thermal Decomposition/Cold Vapor Atomic Absorption using a Teledyne Leeman Labs Hydra IIC Mercury Analyzer. Mercury concentrations in fish are a function of size, with larger and heavier fish having higher concentrations. Fish that are higher on the food chain also have higher THg concentrations. Total Hg concentrations in chain pickerel increased more rapidly with length and weight than in yellow perch, producing THg concentrations in large pickerel (1,255ng/g) that far exceed EPA guidelines (130ng/g) for human consumption.

Based on their position in the food chain, pickerel were expected to have the highest muscle THg concentration, but brook trout from Avery Brook (average length 13cm) had unexpectedly higher THg (177ng/g) than similar sized pickerel (22cm – 94ng/g) and yellow perch (15cm – 77ng/g) from Cooks Pond. Total Hg in Avery Brook surface waters was also higher than that observed in Cooks Pond. This likely reflects differences in watershed flow paths, with the till dominated Avery Brook producing more surface runoff than the stratified drift Pine Barrens at Cooks Pond. Both watersheds appear to have similar areas of MeHg producing wetlands. A comparison between THg in stomach contents with THg in muscle tissue shows less bioconcentration in brook trout than in perch or pickerel. Our results also show that the ratio of stomach content THg to muscle THg is higher in brook trout (0.42) than in either pickerel (0.27) or yellow perch (0.19). This means that for a given concentration of prey mercury, pickerel and yellow perch yield higher THg in muscle tissue. Thus for there to be more THg in Avery Brook trout the amount of mercury in the watershed system must be much greater than in Cooks Pond.