What influences Fish Mercury Levels?

MNRF researchers and partners collected samples from seven fish species across 141 Ontario lakes. They found that variation in mercury concentration among individual fish depended mostly on their age or size. For most species, age was a better predictor of mercury concentration than size. Where a fish was located in the food web and how it grew, influenced its mercury levels less.

Mercury is a widespread contaminant in freshwater ecosystems and is a worldwide concern. Mercury bioaccumulates — meaning it is absorbed more easily than eliminated — so levels in the body increase over time. Mercury also biomagnifies, meaning concentrations increase as you move up the food chain.

This research helps us understand the relative importance of various factors influencing mercury concentrations in Ontario’s fish. Research results are used to inform management decisions. Information about mercury levels is also used to develop provincial fish consumption guides.

For more information on the research, request the research article by email to info.mnrfscience@ontario.ca with the subject line “Requesting Johnston article on mercury variability in northern fish”.

The Guide to Eating Ontario Fish provides easy-to-use information to help choose fish caught from Ontario lakes and rivers to minimize exposure to toxins.