Trace Element Concentrations in Livers of Pacific Harbor Seals (Phoca vitulina richardii) from San Juan County, Washington, USA

Abstract: Approximately 5,000 Pacific harbor seals (Phoca vitulina richardii) reside year-round in San Juan County (SJC), Washington (US) in the center of the binational Salish Sea. We retrospectively analyzed total cadmium (Cd), copper (Cu), iron (Fe), mercury (Hg), magnesium (Mg), manganese (Mn), lead (Pb), selenium (Se), and zinc (Zn) in livers of dead stranded harbor seals (n=57) collected in SJC between 2009 and 2012 to identify age-related and regional patterns of trace element exposure. Consistent with prior studies of contaminants in pinnipeds, Hg, Cd, and Se concentrations increased with age, and Se:Hg molar ratios approached 1:1 in adult seals. Concentrations of Cd and Hg were below putative marine mammal toxicity thresholds. Mercury concentrations were comparable among Salish Sea populations. Although SJC is less urbanized with fewer industrial inputs than South Puget Sound (SPS), SJC nonpups had greater concentrations of Cd, Cu, and Zn, and pups had greater concentrations of Zn compared to SPS seals. We hypothesize these regional differences could be due to prey preference and availability or to natural geochemical processes. Reported concentrations inform future sampling protocols and can assist in tracking long-term temporal and spatial trends of trace elements in marine organisms.