Mercury level rises in Lake Erie walleye

LEAMINGTON, Ontario, May 21 (UPI) -- Mercury levels in Lake Erie walleye appear to be increasing after two decades of steady decline, Canadian scientists said.

The researchers analyzed 5,807 fish samples collected from the Great Lakes between the 1970s and 2007.

Mercury levels in the fish steadily declined from the mid-1970s to 2007 in the upper Great Lakes of Superior and Huron and leveled-off in Lake Ontario walleye between 1990 and 2007, said Satyendra Bhavsar, a researcher with the Ministry of the Environment in Ontario.

In Lake Erie, however, walleye, a popular game fish, showed increased concentrations of mercury, Bhavsar and his team wrote in a recent issue of the journal Environmental Science & Technology.

The increases likely were caused by a combination of factors, including modifications in Lake Erie's food web, which has been invaded by dreissenid mussels and round goby, the scientists concluded.

Government regulations and improved emissions control have greatly reduced mercury emissions in the environment, but their impact on mercury levels in Great Lakes fish is unclear, Bhavsar said.