Isotopic ( δ 15 N ) relationship of pregnant females and their embryos: Comparing placental and yolk‐sac viviparous elasmobranchs

Nitrogen stable isotopes ratios (δ 15 N) were determined for selected tissues (muscle, liver, blood and yolk) of pregnant females and their embryos of a placental viviparous species, the Pacific sharpnose shark ( Rhizoprionodon longurio ), and a yolk‐sac viviparous species, the speckled guitarfish ( Pseudobatos glaucostigmus) . The R. longurio embryo tissues were 15 N enriched compared to the same tissues in the pregnant female, using the difference in δ 15 N (Δδ 15 N) between embryo and adult. Mean Δδ 15 N was 2.17‰ in muscle, 4.39‰ in liver and 0.80‰ in blood. For P. glaucostigmus , embryo liver tissue was significantly 15 N enriched in comparison with liver of the pregnant female (Δδ 15 N mean = 1.22‰), whereas embryo muscle was 15 N depleted relative to the muscle of the pregnant female (Δδ 15 N mean = −1.22‰). Both species presented a significant positive linear relationship between Δδ 15 N and embryo total length ( L T ). The results indicated that embryos have different Δδ 15 N depending on their reproductive strategy, tissue type analysed and embryo L T .