Brood patch size as a field indicator for feather mercury concentration, but not plastic ingestion, in a harvested seabird of the high Arctic: The little auk Alle alle

Northwest Greenland societies substantially rely on subsistence harvest, a part of which consists of little auks (Alle alle), an abundant seabird in the Arctic. Although little auks inhabit remote regions, they are prone to accumulating mercury (Hg) in their tissues and ingesting plastics from their environment while feeding. This entails a broad array of health-related issues, from the birds themselves to their local predators including humans. Here, we examined whether Hg and plastic contamination in little auks were influenced by the birds' age class and breeding status, mirrored by brood patch presence and size. Feather Hg concentrations were higher in birds with large brood patches (adults, currently breeding), compared to younger or non-breeding birds. Feather Hg concentrations also positively correlated with nitrogen stable isotope values in feathers, indicative of trophic position fed in the previous summer. Among the 13 examined auks’ gastrointestinal tract, two (15.4 %) contained large polyethylene fragments (6.55 × 4.10 mm, 49.45 mg on average); their occurrence was not found to relate to brood patch size. Although future research is needed on Hg accumulation in internal tissues, our results suggest that consuming adult little auks and the birds' gastrointestinal tracts may increase health-related risks for Arctic communities.