Quantifying Maternal Transfer of Trace Elements and Stable Isotopes in the Endangered Pelagic Thresher Shark (Alopias Pelagicus)

Abstract

To quantify maternal provisioning of nutrients in the pelagic thresher shark ( Alopias pelagicus ) and the potential for negative impacts, the concentrations of trace elements (essential: Co, Cr, Cu, Mn, Ni, Se, and Zn; nonessential: As, Ba, Cd, Hg, and Pb) and fractionation of stable isotopes (δ 13 C and δ 15 N) were analyzed in the muscle and liver of 10 pregnant females and 18 associated embryos. Essential trace elements were observed to be offloaded at higher concentrations to embryos, with the exception of Zn and Ni in liver, while nonessential trace elements were unevenly distributed between maternal-embryo tissues.Observed Hg concentrations were at levels considered toxic in A. pelagicus , but the Se: Hg molar ratios in all embryonic tissues were all greater than one. A negative correlation was observed between transfer ratios and concentrations of all elements in maternal tissue, indicating the existence of a regulatory mechanism in maternal ovaries of A. pelagicus . Compared with maternal specimens, associated embryos had higher δ 13 C and δ 15 N values in muscle and liver tissue. Negative correlations were observed between δ 13 C, δ 15 N, and Δδ 13 C values and precaudal length in embryonic muscle tissue potentially reflecting either a dietary-habitat shift in pregnant females during the latter period of gestation or a physiological change modifying fractionation. Higher concentrations of essential elements are linked to potential benefits for embryos during early development, levels of Hg suggested a degree of anthropogenic impact with unknown consequences while the directionality of isotopic fractionation could suggest a potential reproductive migration as a protective mechanism for birthing.

Keywords: maternal investment, stable isotope, migration, diet change, embryo