Mercury in fish in the Derwent Estuary, Tasmania, and its relation to the position of the fish in the food chain

Abstract

Total mercury concentrations are reported for 258 individuals representing 16 species of finfish from the Derwent Estuary, Tasmania. Mercury concentrations in the muscle tissue varied between undetectable levels and a value of 2.0 mg/kg in one specimen of a species of shark. Irrespective of species, the area encompassing Ralphs Bay contained a higher percentage of fish with mercury concentrations in excess of the Tasmanian Food Regulation limit of 0.5 mg/kg than any other area of the Estuary. RaIphs Bay is the area in which oysters were found in a previous study to contain extraordinarily high concentrations of other heavy metals, particularly zinc, cadmium and copper. The fish's position in the food chain appeared to be an important factor determining its mercury content. Approximately 51 % of individual fish of species whose diet consists predominantly of other fish had mercury concentrations in excess of 0.5 mg/kg. In contrast, 24% of invertebrate predators and only 7 % of individuals of herbivorous habit had mercury concentrations in excess of 0.5 mg/kg.