Click here to view linked References 20201266 and SIP 20210215), "Biogeoquímica de elementos traza en sistemas costeros influenciados por minería de cobre" (Grant number SIP 20200709), "Biogeoquímica de elementos mayores y traza en sistemas costeros" (Grant number SIP 20211002) and "Modelación ecogeoquímica de sistemas costeros hacia una salud integral" (Grant number SIP 2152). FGM, AJMR thanks the Instituto Politécnico Nacional for their fellowships (COFFA and EDI).
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 .
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