Mercury contamination in the endocrine glands of Black-tailed Gulls Larus crassirostris on Kabushima (Kabu Island), Japan

A colony of about 30 000 pairs of Black-tailed Gull Larus crassirostris nest on Kabushima (Kabu Island), which is located on the northeast mainland coast of Japan (Sanriku Coast, Honshu Island). There, the surface-water Hg concentration is higher than in the North Pacific Ocean. We collected carcasses from the breeding colony to assess the level of mercury (Hg) contamination. We measured Hg concentrations in 10 body tissues, including the endocrine glands. The relative mercury concentrations in the tissue samples (µg/g dry weight) were as follows: adrenal glands > livers > kidneys > blood > pituitaries > gonads > breast muscles > thyroid glands > pancreases > brain stems. Correlations existed between blood mercury levels and all body tissues except for the adrenal glands. Based on these results, we suggest that mercury levels in blood may not be a good indicator for hypothalamic-pituitary-adrenal axis impacts in Black-tailed Gulls.