Temporal Mercury Dynamics and Diet Composition in the Mimic Shiner

Abstract

Changes in total mercury concentration (T-Hg), diet, and growth were monitored in three age-classes and four cohorts of mimic shiners Notropis volucellus throughout the ice-free season of 1995 and in early May 1996 and 1997 in Devils Lake, Wisconsin. All age-classes of fish fed exclusively on Daphnia in early spring and late fall but had a mixed diet during the summer consisting of zooplankton, other invertebrates, and filamentous algae. Concentration of methyl Hg in Daphnia varied during the summer. Concentration of T-Hg in age-1 fish also varied during the summer, but all age-classes increased in T-Hg concentration during winter. Body burden increased steadily throughout the year for all age-classes and cohorts. Each successively older age-class of fish had increasingly higher concentrations of T-Hg and body burdens. The T-Hg concentration and body burden were significantly different between cohorts in early spring for age-1 and age-2 fish. Differences between cohorts corresponded to differences in Hg concentrations in the water and Daphnia during the cohort's year of birth. Our results suggest that small planktivorous fish are a useful sentinel for monitoring short-term changes in the availability of Hg in lakes.