Sainte-Marguerite-3 Hydroelectric Development : environmental monitoring 2005 : changes in mercury and fish communities

This paper presented the results of a fish monitoring survey of the Sainte-Marguerite-3 (SM3) reservoir. The survey monitored changes in mercury levels before and after the impoundment of the reservoir. The study showed that fish populations grew as a results of increases in organic matter. Fishing yields rose by a factor of 5 due to increases in lake whitefish and northern pike. Increases in longnose suckers were also observed. No piscivorous species were found in the stomachs of northern pike in 2005. The main prey for northern pike were lake whitefish. Mean mercury levels for fish of a standardized length increased by a factor ranging from 5 to 8 in the SM3 reservoir. Increases were attributed to mercury methylation as a result of the decomposition of organic plant matter following impoundment. It was concluded that guidelines developed in 2003 are still valid for the SM3 reservoir. However, recommended consumption levels of whitefish in the adjoining SM2 reservoir have been decreased from 8 to 4 meals per month