Analysis of narwhal tusks reveals lifelong feeding ecology and mercury exposure
Résumé
The ability of animals to respond to changes in their environment is critical to their persistence. In the
Arctic, climate change and mercury exposure are two of the most important environmental threats for
top predators. Rapid warming is causing precipitous sea-ice loss, with consequences on the distribution,
composition, and dietary ecology of species and, thus, exposure to food-borne mercury. Current
understanding of global change and pollution impacts on Arctic wildlife relies on single-time-point individual
data representing a snapshot in time. These data often lack comprehensive temporal resolution and
overlook the cumulative lifelong nature of stressors as well as individual variation. To overcome these challenges,
we explore the unique capacity of narwhal tusks to characterize chronological lifetime biogeochemical
profiles, allowing for investigations of climate-induced dietary changes and contaminant trends.
Using temporal patterns of stable isotopes (d13C and d15N) and mercury concentrations in annually deposited
dentine growth layer groups in 10 tusks from Northwest Greenland (1962–2010), we show surprising
plasticity in narwhal feeding ecology likely resulting from climate-induced changes in sea-ice cover, biological
communities, and narwhal migration. Dietary changes consequently impacted mercury exposure primarily
through trophic magnification effects. Mercury increased log-linearly over the study period, albeit
with an unexpected rise in recent years, likely caused by increased emissions and/or greater bioavailability
in a warmer, ice-free Arctic. Our findings are consistent with an emerging pattern in the Arctic of reduced
sea-ice leading to changes in the migration, habitat use, food web, and contaminant exposure in Arctic top
predators.