Mercury Elimination by a Top Predator, Esox lucius

Top-level piscivores are highly sought after for consumption in freshwater fisheries, yet these species contain the highest levels of the neurotoxin monomethylmercury (MMHg) and therefore present the greatest concern for MMHg exposure to humans. The slow elimination of MMHg is one factor that contributes to high levels of this contaminant in fish; however, little quantitative information exists on elimination rates by top predators in nature. We determined rates of MMHg elimination in northern pike (Esox lucius) by transferring fish that had naturally accumulated isotope-enriched MMHg (spike MMHg) through a whole-lake Hg loading study to a different lake. Over a period of similar to 7 y, pike were periodically recaptured and a small amount of muscle tissue was extracted using a nonlethal biopsy. Spike total mercury (THg) persisted in muscle tissue throughout the entire study despite discontinuing exposure upon transfer to the new lake. Spike THg burdens increased for the first similar to 460 d, followed by a decline to 65% of original burden levels over the next 200 d, and subsequently reached a plateau near original burden levels for the remainder of the study. We estimated the half-life of muscle THg to be 3.3 y (1193 d), roughly 1.2- to 2.7-fold slower than predicted by current elimination models. We advocate for further long-term field studies that examine kinetics of MMHg in fish to better inform predictive models estimating the recovery of MMHg-contaminated fisheries.