Abstract
Total mercury (THg) concentrations were measured for different life-history types of Northern Dolly Varden (Salvelinus malma malma) from the Babbage River, Yukon Territory, Canada to test hypotheses regarding the influence of life-history type, trophic position, and growth rate on THg tissue concentrations. In contrast to other northern anadromous fish species, higher measured THg concentrations were found in the anadromous life-history types. Standardization for common age, however, indicated that anadromous fish had lower THg concentrations than freshwater resident life-history types. δ15N was the most important factor in explaining observed differences among the individuals regardless of life-history types, with growth rate also contributing to explain among-individual variation. The contrast of higher absolute, but lower age- and size-adjusted THg levels in anadromous fish was explained by a combination of two counteracting mechanisms, including: (1) a switch to feeding at higher trophic levels and the use of more THg contaminated marine prey, and (2) somatic growth dilution that, with increasing growth efficiency, decreases THg as fish grow and age. Results underscore the importance of considering life-history variation in addition to trophic patterns, and fish sizes and age when interpreting mercury concentrations in fish with varying life histories.
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