Blood mercury concentration is related to body condition, breeding success and trophic ecology in Brown Skuas (Stercorarius antarcticus)

Abstract

Mercury (Hg) is a pervasive environmental pollutant that affects seabirds´ physiology with short- and long-term fitness consequences. Brown Skuas (Stercorarius antarcticus) are opportunistic top predators and scavengers, and therefore are effective bioindicators of contamination. We measured total mercury (THg) concentration and the stable isotopes of carbon (δ13C, a proxy of feeding habitat) and nitrogen (δ15N, a proxy of trophic position/diet) in blood from breeding adult Brown Skuas at Esperanza/Hope Bay (Antarctic Peninsula) (N=49). The aim of the study was to evaluate the influence of individual traits (body condition and sex) and foraging ecology (δ13C and δ15N values) on Hg exposure, and to determine the relationship between THg concentration with body condition and breeding success. We fitted general linear models, and the most parsimonious model included sex, sampling date, breeding season, body condition and δ15N as variables. Mean ± SD THg concentration in blood was 0.82±0.36 µg g-1dw, and was higher in males (N=25, 0.89±0.38 µg g-1dw) than in females (N=24, 0.75±0.33 µg g-1dw). Adults with higher THg showed lower body condition, and in females, also lower breeding success. In addition, a positive association was observed between THg concentration and δ15N reflecting bioaccumulation from prey. Males showed higher THg loads than females, probably because females can deposit Hg in eggs, which may explain why females with higher THg were less likely to fledge chicks. Together, these results indicate that Hg has deleterious effects on reproduction in adult skuas, with potential long-term repercussions at the population level.