In utero elemental tags in vertebrae of the scalloped hammerhead shark Sphyrna lewini reveal migration patterns of pregnant females

Abstract

Vertebral microchemistry recently allowed to infer the migration patterns of the scalloped hammerhead shark Sphyrna lewini in the Mexican Pacific, however conclusions regarding the movements of reproductive females were hindered by the small sample size. Considering that S. lewini is a placental viviparous species, maternal supply of nutrients to the embryos might influence their vertebral microchemistry while in utero and provide intrinsic markers of the pregnant female environmental histories. This hypothesis was tested before attempting to infer the migration patterns of pregnant females through the analyses of the in utero elemental profiles quantified in the vertebrae of coastal young-of-the-year (‘YOY’). Vertebrae were obtained from sharks captured along the Mexican Pacific coast in 2016. Vertebral microchemistry was quantified using laser ablation inductively-coupled plasma mass spectrometry. Elemental signatures at vertebral edge were consistent between each pregnant female and her embryos demonstrating the viability of employing in utero elemental signatures as a maternal tag of the gestation-related environmental histories. Analyses of the YOY in utero Sr:Ba and Pb:Ca profiles suggested that pregnant females either (1) progressively migrated offshore before quickly returning to coastal habitats before term or (2) remained nearshore during complete gestation. Considering the endangered status of S. lewini, current management measures may be insufficient for the sustainable management of the population as pregnant females may be particularly susceptible to fisheries when remaining nearshore or entering coastal habitats prior to pupping.