Maternal transfer of mercury in a late-term litter of blue shark (Prionace glauca) from the Gulf of California.

Blue sharks (Prionace glauca) are circumglobal predators that can accumulate elevated mercury (Hg) concentrations due to their high trophic position. This study measured Hg in the muscle and liver of a pregnant female and her complete litter of 34 late-term embryos collected from the southwestern Gulf of California to assess tissue-specific maternal-embryonic Hg patterns and absolute burdens. Maternal dry-weight Hg concentrations were higher in muscle (4.75 μg g-1) and liver (0.51 μg g-1) than mean (± standard deviation) embryonic concentrations (0.42 ± 0.04 μg g-1 and 0.07 ± 0.01 μg g-1, respectively. Embryo-to-maternal concentration ratios averaged 8.91% in muscle and 14.18% in liver. Mercury concentrations did not differ between sexes and were not significantly related to embryo total length or body mass. Embryonic hepatosomatic index was positively associated with muscle Hg concentration (p = 0.005), whereas muscle and liver Hg concentrations were not significantly correlated. An absolute-burden approach estimated a combined muscle-plus-liver Hg burden of 637.8 μg for the complete litter, corresponding to 3.47% of the estimated maternal muscle-plus-liver burden. This maternal-to-litter burden ratio complements tissue-specific concentration ratios but does not represent a whole-body Hg mass balance. These findings provide the first tissue-resolved evidence of prenatal Hg exposure in a blue shark reproductive event and demonstrate that late-term embryos carry measurable Hg burdens before birth, while highlighting the importance of tissue-specific physiology in maternal-embryonic Hg dynamics.