Manipulation of sport fish growth to reduce mercury bioaccumulation on a whole-lake scale

Integration of mercury (Hg) into aquatic food webs results in contamination in fish that present health concerns for fish consumers.  Here we describe a whole-lake study assessing the efficacy of stocking prey fish as a means of increasing growth in northern pike (Esox lucius) to reduce Hg concentrations in ~50 days.  A pond component served as a reference and to evaluate the relative importance of manipulating pike densities to increase growth rates and reduce Hg concentrations.  We collected repeated measures of Hg concentrations from individuals before and after the manipulation.  Pike fed prey fish showed a significant relationship between weight gain and reduction in Hg concentration, decreasing up to 50%.  The lake manipulation showed that stocking disproportionately benefited large pike (presumably those with the highest Hg burdens) rather than small pike.  Pike density reductions did not influence Hg concentrations, though this has been observed in other studies.  The results highlight the need to conduct manipulations on a whole-system scale.  Although successful, stocking is likely unfeasible economically and ecologically due to a continuously growing biomass that must be increasingly subsidized.  We recommend creating food webs with fast growing predators as a sustainable method of reducing Hg bioaccumulation to protect human health.