Publication Summary

This article was published in the Journal of Freshwater Ecology, Vol. 17, No. 4, pp. 621-633, December 2002.

The article reports differences in mercury (Hg) concentrations among Lake Whatcom fish occupying different trophic levels. The highest Hg concentrations were found in predaceous smallmouth bass and large yellow perch (means of 0.49 and 0.20 ug/g, respectively) followed by omnivorous brown bullhead (0.16 ug/g), zooplanktivorous kokanee (0.12 ug/g), benthivorous pumpkinseed (0.10 ug/g), and herbi-detritivorous signal crayfish (0.10 ug/g). Predaceous cutthroat trout had low mean Hg (0.07 ug/g), possibly due to the small size of specimens analyzed. The much larger bass and perch showed a strong positive relationship between length and Hg, illustrating the magnification of Hg due to trophic position.

Tissue samples from six species of fish and one species of crayfish from Lake Whatcom, Washington were analyzed for total mercury content in late spring 2000. Predaceous smallmouth bass (Micropterus dolomieu) displayed the highest levels of mercury (mean ± SE, range = 0.49 ± 0.03, 0.10 - 1.84 mg/kg, n = 95), followed by omnivorous yellow perch (Perca flavescens) (0.20 ± 0.03, 0.04 - 0.87 mg/kg, n = 30) and brown bullhead (Ameiurus nebulosus) (0.16 ± 0.06, 0.03 - 0.79 mg/kg, n = 13), zooplanktivorous kokanee (Oncorhynchus nerka) (0.12 ± 0.01, 0.07 - 0.25 mg/kg, n = 30), benthivorous pumpkinseed (Lepomis gibbosus) (0.10 ± 0.01, 0.03 - 0.28 mg/kg, n = 30), and herbi-detritivorous signal crayfish (Pacifasticus leniusculus) (0.10 ± 0.01, 0.03 - 0.54 mg/kg, n = 45). Predaceous cutthroat trout (Oncorhynchus clarki) had the lowest levels (0.07 ± 0.01, 0.03 - 0.20 mg/kg, n = 30), possibly related to the low trophic level of the smaller size classes captured, natal stream residency of wild fish, or hatchery origins of stocked fish. The fastest rates of mercury bioaccumulation were found in brown bullhead, smallmouth bass, signal crayfish, and yellow perch as indicated by the slopes of their log-transformed mercury concentration-age regression lines. The slopes for cutthroat trout, kokanee, and pumpkinseed suggested very slow uptake in these species.