Predicting Mercury Concentration in Fish Using Mass Balance Models

Abstract

Mass balance models have frequently been used with laboratory-derived bioenergetic models to examine the accumulation of mercury (Hg) in fish. The accumulation of Hg in fish has usually been successfully described by these models. However, this has generally been achieved by adjusting the parameters of these models until there was a close fit between observed and predicted values. In this study, we present a simple Hg mass balance model (MMBM) to predict Hg concentration in fish. This MMBM was applied with three methods of estimating food consumption rates to predict Hg concentration in three freshwater fish species. The MMBM accurately predicted the accumulation of Hg in the three fish species examined in this study when it was combined with food consumption rates that were determined with a radioisotopic method. The MMBM tended to underestimate Hg concentration in fish when it was combined with food consumption rates determined using laboratory-derived bioenergetic models, possibly because activity costs derived under laboratory conditions do not adequately represent activity costs of fish in the field. When feeding rates were estimated with a bioenergetic model implemented with site-specific estimates of activity costs, the MMBM accurately predicted the concentration of Hg in fish. Therefore, until activity costs can be accurately estimated in situ, predictions obtained with the MMBM implemented with a laboratory-derived bioenergetic model should be interpreted cautiously.