Mother–embryo isotope fractionation in the pygmy devilray Mobula kuhlii cf. eregoodootenkee

Abstract

We determined stable-isotope ratios for replicate muscle tissues in 13 gravid Mobula kuhlii cf. eregoodootenkee (110.4–120.4 cm disc width; WD) and their embryos (7.0–42.3 cm WD) and also yolks and histrotroph, to assess the potential implications for juvenile nutrition and habitat use. Irrespective of their development in the uterus, embryos had similar δ13C values in their muscle tissue as the mothers and both had greater values than in the histotroph. During gestation, δ13C values increased across all sample types. However, while embryo muscle tissue and the histotroph were associated with increasing 15N levels during embryonic development, this was depleted in the mothers’ muscle tissue and yolk. Although speculative, the observed variation in stable-isotope ratios might imply a dietary shift among gravid females during their early gestation. Irrespective of the underlying mechanisms, the results indicate neonates will have relatively greater δ15N values than post-partum females, which would probably confound juvenile foraging-ecology estimates.