Reduction of mercury concentration in fish through intensive fishing of lakes: A preliminary testing of assumptions

摘要

Intensive fishing of lakes has been indicated in the literature as a means of reducing mercury concentrations in fish. However, the controlling process by which this occurs remains unclear. Three assumptions are generally put forward to explain the reduction. The first is that intensive fishing would affect the total mercury balance of the lake and reduce the mercury bioaccumulation in fish. The second is that the fish diet would be affected, especially for piscivorous fish feeding on smaller prey fish with lower mercury concentration following intensive fishing of larger prey fish. The third assumption is that the rate of growth of the fish remaining after intensive fishing would increase since competition for food would generally be reduced. Testing of these assumptions were made using fish data from three natural lakes located in the James Bay territory of northern Quebec, Canada, where intensive fishing occurred in 1998. Dominant species of fish were considered and mass and mercury concentrations of individual fish were expressed as a function of fish age. A bioenergetics model was used to compute the rate of feeding of fish. A mercury bioaccumulation model was used to relate mercury concentration in fish to intake of mercury by fish through food diet. Results computed for the lakes investigated have indicated the effects of these processes taken separately and the conditions under which they may be controlling the reduction of mercury concentration in fish.