Methyl mercury in brown trout (Salmo trutta) in Arahura River, New Zealand

Abstract

Methyl mercury (MeHg) concentrations were determined in brown trout (Salmo trutta) from the Arahura River, on the West Coast of the South Island, New Zealand. Trout fell into two groups, one with very low MeHg concentrations (0.002–0.018 μg g^‐1) and the other with relatively higher MeHg concentrations (0.096–0.220 μg g^‐1). Trout elevated in MeHg had a terrestrial carbon signature and fed at a higher trophic level than trout with low MeHg concentrations. The strontium: calcium ratio in the otoliths of two fish revealed that a trout with low MeHg values had lived in the sea for part of its life, whereas a trout with higher MeHg concentration had lived solely in the river. Sea‐running trout were eating prey of marine origin, whereas the river‐resident fish were consuming prey at a higher trophic level in the food web, which may result in markedly different MeHg concentrations in these fish.

Keywords:

• diet
• trophic level
• trout life history