Deep-ocean foraging northern elephant seals bioaccumulate persistentorganic pollutants

As top predators in the northeast Pacific Ocean, northern elephant seals (Mirounga angustirostris) are vulnerable to bioaccumulation of persistent organic pollutants (POPs). Our study examined a suite of POPs in blubber (inner and outer) and blood (serum) of free-ranging northern elephant seals. For adult females (N=24), we satellite tracked and sampled the same seals before and after their approximately sevenmonthlong foraging trip.Formales,we sampled different adults and sub-adults before (N=14) and after (N=15) the same foraging trip. For females,we calculated blubber burdens for all compounds. The highest POP concentrations in males and females were found for ΣDDTs andΣPCBs. In blubber and serum, males had significantly greater concentrations than females for almost all compounds. For males and females,ΣDDT andΣPBDEs were highly correlated in blubber and serum.While ΣPCBs were highly correlatedwithΣDDTs andΣPBDEs in blubber and serum formales,ΣPCBs showed weaker correlationswith both compounds in females. As females gainedmasswhile foraging, concentrations of nearly all POPs in inner and outer blubber significantly decreased; however, the absolute burden in blubber significantly increased, indicating ingestion of contaminantswhile foraging. Additionally,we identified three clusters of seal foraging behavior, based on geography, diving behavior, and stable carbon and nitrogen isotopes, which corresponded with differences inΣDDTs,ΣPBDEs, MeO-BDE 47, as well as the ratio ofΣDDTs toΣPCBs, indicating the potential for behavior to heighten or mitigate contaminant exposure. The greatest concentrations ofΣDDTs and ΣPBDEs were observed in the cluster that foraged closer to the coast and had blood samples more enriched in 13C. Bioaccumulation of POPs by elephant seals supports mesopelagic food webs as a sink for POPs and highlights elephant seals as a potential sentinel of contamination in deep ocean food webs.