Document Type

Master's Thesis

Degree Name

Master of Science (M.S.)


Moss Landing Marine Laboratories


To determine trace element concentrations in the Pacific harbor seal (Phoca vitulina richardii), live (n=189) and dead seals (n=53) were sampled throughout central and northern California from March 2003 to January 2005. Total mercury (THg) concentrations were determined in blood and hair of live harbor seals and hair and liver of dead harbor seals. Concentrations of monomethyl mercury (MeHg), selenium (Se), and lead (Pb) additionally were determined in liver of dead harbor seals. To assess trophic level, carbon and nitrogen stable isotopes were examined in liver. Age class assignments of live harbor seals were based on morphometrics, and ages of dead harbor seals were determined by cementum annuli in teeth. 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 d15N (P<0.001); whereas, MeHg concentrations in liver increased with age exponentially with an asymptote at approximately 1.3 ppm wet weight. MeHg expressed as a percentage of THg (% MeHg) was best described by a decay function (r2=0.7961, P<0.001). As harbor seals aged, % MeHg decreased to a minimum and remained constant. Se in the liver also increased with age and was in equilmolar ratios with THg in adults; whereas, molar ratio of Se:THg in pups did deviate from a 1:1 ratio. Significant differences among locations in THg concentrations in blood and hair were not detected. Assessing the possible affect of location of sampling on mercury concentrations, however, is confounded and limited by lack of equal sample sizes for basic age and sex cohorts.


Thesis (M.S.) Division of Science and Environmental Policy. Moss Landing Marine Laboratories