Influence of migration range and foraging ecology on mercury accumulation in Southern Ocean penguins

In order to evaluate mercury (Hg) accumulation patterns in Southern Ocean penguins, we measured Hg concentrations and carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios in body feathers of adult Adélie (Pygoscelis adeliae), gentoo (Pygoscelis papua), and chinstrap (Pygoscelis antarctica) penguins living near Anvers Island, West Antarctic Peninsula (WAP) collected in the 2010/2011 austral summer. With these and data from Pygoscelis and other penguin genera (Eudyptes and Aptenodytes) throughout the Southern Ocean, we modelled Hg variation using δ¹³C and δ¹⁵N values. Mean concentrations of Hg in feathers of Adélie (0.09 ± 0.05 μg g^-1) and gentoo (0.16 ± 0.08 μg g^-1) penguins from Anvers Island were among the lowest ever reported for the Southern Ocean. However, Hg concentrations in chinstrap penguins (0.80 ± 0.20 μg g^-1), which undertake relatively broad longitudinal winter migrations north of expanding sea ice, were significantly higher (P < 0.001) than those in gentoo or Adélie penguins. δ¹³C and δ¹⁵N values for feathers from all three Anvers Island populations were also the lowest among those previously reported for Southern Ocean penguins foraging within Antarctic and subantarctic waters. These observations, along with size distributions of WAP krill, suggest foraging during non-breeding seasons as a primary contributor to higher Hg accumulation in chinstraps relative to other sympatric Pygoscelis along the WAP. δ¹³C values for all Southern Ocean penguin populations, alone best explained feather Hg concentrations among possible generalized linear models (GLMs) for populations grouped by either breeding site (AICc = 36.9, w_i = 0.0590) or Antarctic Frontal Zone (AICc = 36.9, w_i = 0.0537). Although Hg feather concentrations can vary locally by species, there was an insignificant species-level effect (w_i < 0.001) across the full latitudinal range examined. Therefore, feeding ecology at breeding locations, as tracked by δ¹³C, control Hg accumulation in penguin populations across the Southern Ocean.