Effects of Age, Colony, and Sex on Mercury Concentrations in California Sea Lions
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We measured total mercury (THg) concentrations in California sea lions (Zalophus californianus) and examined how concentrations varied with age class, colony, and sex. Because Hg exposure is primarily via diet, we used nitrogen (δ 15N) and carbon (δ 13C) stable isotopes to determine if intraspecific differences in THg concentrations could be explained by feeding ecology. Blood and hair were collected from 21 adult females and 57 juveniles from three colonies in central and southern California (San Nicolas, San Miguel, and Año Nuevo Islands). Total Hg concentrations ranged from 0.01 to 0.31 μg g−1 wet weight (ww) in blood and 0.74 to 21.00 μg g−1 dry weight (dw) in hair. Adult females had greater mean THg concentrations than juveniles in blood (0.15 vs. 0.03 μg−1 ww) and hair (10.10 vs. 3.25 μg−1 dw). Age class differences in THg concentrations did not appear to be driven by trophic level or habitat type because there were no differences in δ 15N or δ 13C values between adults and juveniles. Total Hg concentrations in adult females were 54 % (blood) and 24 % (hair) greater in females from San Miguel than females from San Nicolas Island, which may have been because sea lions from the two islands foraged in different areas. For juveniles, we detected some differences in THg concentrations with colony and sex, although these were likely due to sampling effects and not ecological differences. Overall, THg concentrations in California sea lions were within the range documented for other marine mammals and were generally below toxicity benchmarks for fish-eating wildlife.
All animals were sampled in conjunction with other studies under National Marine Fisheries Permit Nos. 14676, 16087, 17115, and 17952 and approved Institutional Animal Care and Use Committee protocols from the University of California Los Angeles, University of California San Diego, and the National Marine Mammal Laboratory. We thank the United States Navy (especially J. Ugoretz), the staff at Channel Islands National Park and Channel Islands Aviation for logistical support, rangers at Año Nuevo State Reserve, and all of the volunteers who assisted in animal capture and sample collection. We especially thank P. Ponganis, M. Tift, K. Prager, and J. Lloyd-Smith. Funding support for E.A. McHuron was provided by the Office of Naval Research (ONR N00014-13-1-0134), the Joint Industry Programme (JIP22 07-23), and a Friends of Long Marine Laboratory Student Research and Education Award. Funding support for J.T. Ackerman was provided by the U.S. Geological Survey Western Ecological Research Center. The use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the United States Government.
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