Trace element concentrations in the Pacific harbor seal (Phoca vitulina richardii) in central and northern California

To determine concentrations of trace elements (THg, MeHg, Se, and Pb) in tissues of the Pacific harbor seal (Phoca vitulina richardii), live (n = 186) and dead seals (n = 53) were sampled throughout central and northern California from March 2003 to January 2005. There were significant differences in THg concentrations in blood and hair based on age (p < 0.001). Adult male harbor seals had greater THg concentrations in their hair than adult female harbor seals (p < 0.003). THg concentrations in liver increased linearly with age and δ15N (p < 0.001); whereas, MeHg concentrations in liver increased exponentially until approximately 5 years of age with an asymptote at 1.3 μg/g wet weight. MeHg expressed as a percentage of THg (%MeHg) was best described by a decay function (r2 = 0.796, p < 0.001), decreasing to a minimum at 4 years of age. Hepatic Se increased with age and was in equimolar ratios with THg in adults; whereas, molar ratio of Se:THg in pups deviated from a 1:1 ratio. Significant differences among study locations in THg concentrations in blood and hair were not detected. Assessing the possible effect of sampling location on Hg concentrations, however, was confounded and limited by lack of equal sample sizes for basic age and sex cohorts, a common dilemma in pinniped research.