Foraging plasticity diversifies mercury exposure sources and bioaccumulation patterns in the world's largest predatory fish
Résumé
Large marine predators exhibit high concentrations of mercury (Hg) as neurotoxic methylmercury, and the
potential impacts of global change on Hg contamination in these species remain highly debated. Current
contaminant model predictions do not account for intraspecific variability in Hg exposure and may fail to reflect
the diversity of future Hg levels among conspecific populations or individuals, especially for top predators
displaying a wide range of ecological traits. Here, we used Hg isotopic compositions to show that Hg exposure
sources varied significantly between and within three populations of white sharks (Carcharodon carcharias) with
contrasting ecology: the north-eastern Pacific, eastern Australasian, and south-western Australasian populations.
Through Δ200Hg signatures in shark tissues, we found that atmospheric Hg deposition pathways to the marine
environment differed between coastal and offshore habitats. Discrepancies in δ202Hg and Δ199Hg signatures
among white sharks provided evidence for intraspecific exposure to distinct sources of marine methylmercury,
attributed to population and ontogenetic shifts in foraging habitat and prey composition. We finally observed a
strong divergence in Hg accumulation rates between populations, leading to three times higher Hg concentra-
tions in large Australasian sharks compared to north-eastern Pacific sharks, and likely due to different trophic
strategies adopted by adult sharks across populations. This study illustrates the variety of Hg exposure sources
and bioaccumulation patterns that can be found within a single species and suggests that intraspecific variability
needs to be considered when assessing future trajectories of Hg levels in marine predators.
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