Mercury Bioaccumulation in Rainbow Trout (Oncorhynchus mykiss) and the Trout Food Web in Lakes Okareka,Okaro, Tarawera,Rotomahana and Rotorua,New Zealand

Methyl mercury (Hg) was determined in rainbow trout (Oncorhynchus mykiss) and organisms in the lower tropic levels: smelts (Retropinna retropinna), bullies (Gobiomorphus cotidianus), koura (Paranephrops planifrons); and zooplankton (Daphnia carinata and Calamoecia lucasi) in Lakes Okareka, Okaro, Tarawera, Rotorua and Rotomahana, New Zealand. Water concentrations of total Hg (Hg_T) and methyl Hg were also measured. Mean methyl Hg concentrations in the trout, the prey species (smelts, bullies and koura) and zooplankton increased linearly with mean Hg_T and methyl Hg chloride (CH₃HgCl) concentrations in water. Most of the bio-magnification of methyl Hg occurred in the lower trophic levels of the trout food web (10^4.72) between the zooplankton and water. The bioaccumulation factors between the forage fish and zooplankton were 10^0.73 for bullies and 10^1.06 for smelt. Methyl Hg was 10^0.41 to 10^0.95 times greater in the trout then their prey.