Historical Changes in Mercury Contamination in Michigan Walleyes (Stizostedion vitreum vitreum)

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Abstract
Mercury concentrations in Michigan walleyes (Stizostedion vitreum vitreum) are more variable among localities than between recent and historical samples within localities. Increases in mercury concentrations were noted in the recent populations of lakes Cadillac and Mitchell, Lake Gogebic, and western Lake Erie. Walleyes in four of seven localities showed no statistically significant increases in the level of mercury contamination over the past 40 yr. Mercury values over 0.5 ppm are common only on Isle Royale, in Saginaw Bay, and in western Lake Erie. Walleyes from Houghton Lake, Bear Lake, and lakes Cadillac and Mitchell show low levels of mercury contamination.Methods for validly comparing preserved and fresh specimens were established by tests to determine the weight loss through dehydration in preservation. In 74% alcohol, muscle tissue of medium to large walleyes dehydrates to about 70% of the fresh weight in the first year.Mercury concentration in walleye muscle from recent and old museum collections is positively correlated with age and size. Considerable variation in concentration exists not only between geographic localities, but within populations, and even within subsamples of the same tissue.

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