SS3.12 Large Scale Ecosystem Manipulations
Date: Thursday, June 13, 2002
Time: 3:00:00 PM
Location: Carson C
 
DoireJ, Université du Québec à Montréal, Montréal, Canada, janvier79@hotmail.com
Lucotte, M, , Université du Québec à Montréal, Montréal, Canada, lucotte.marc_michel@uqam.ca
Fortin, R, , Université du Québec à Montréal, Montréal, Canada, 
Verdon, R, , Hydro-Québec, Montréal, Canada, verdon.richard@hydro.qc.ca
 
INFLUENCE OF INTENSIVE FISHING ON FISH DIET IN NATURAL LAKES OF NORTHERN QUEBEC: USE OF STABLE NITROGEN AND CARBON ISOTOPES.
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In 1998, an intensive fishing project was begun in natural lakes of the Némiscau region, Northern Quebec. In Scandinavian studies, intensive fishing was found to mitigate the mercury problem in fish, but the mecanisms of reduction are still unknown. One explanation for this observation is that the diet of the fish remaining in the lake after the intensive fishing changes. This effect might be especially prominent in top predators that begin to feed on prey lower in the food chain which are less contaminated. It is known that the use of nitrogen and carbon stable isotopes gives accurate and integrated information about the diet and the trophic level of animals. This method was used with fish caught during the summers of 1998 and 2001, before and after intensive fishing, respectively. First results show that the original trophic levels of the fish remaining three years after intensive fishing have not change, even for top predators (walleyes and northern pikes). Therefore, biodilution is a more likely hypothesis to explain the reduction of Hg found in fish.