Contaminant Concentration Trends in Lake Ontario Lake Trout (Salvelinus Namaycush): 1977 to 1988

Abstract

A regression model was used to determine the trend in time and the effects of sampling site, age, and weight on DDE, PCB, mirex, dieldrin, chlordane, and mercury concentrations in lake trout from Lake Ontario from 1977 to 1988. The model allows the use of the entire data set collected by the Canadian Federal Department of Fisheries and Oceans monitoring program for lake trout in this lake up to 1988, and provides estimates of logarithmic mean concentrations in each age group independent of the overall (across all ages) contaminant: body size relationship. Mercury concentrations decreased steadily during the study period with a half life of 11 years. DDE concentrations decreased rapidly from 1977 to 1980 but then remained relatively constant. Mirex concentrations generally decreased, but with much year-to-year variation. Dieldrin concentrations decreased from 1978 to 1988, but chlordane concentrations remained relatively constant. PCB concentrations decreased from 1977 to 1981, increased in 1982 until 1984, and decreased again in 1985. The overall trend in PCB concentrations was a gradual decline with a half life of roughly 10 years. Deviations about this trend were closely related to the rate of growth of the alewife population, a principal food of lake trout, suggesting that food web interactions play an important role in regulating PCB concentrations in lake trout. Lipid concentrations in lake trout also decreased from 1977 to 1988, complicating interpretation of the time trends in the lipid soluble organic contaminants. PCB, DDE, and mirex concentrations in trout increased from east to west in Lake Ontario. All contaminant concentrations increased with increasing age and body size, but the body size effect was less within an age class than across age classes.