Patterns of mother-embryo isotope fractionation in batoids vary within and between species

Patterns of mother-embryo fractionation of ¹³C and ¹⁵N were assessed for their predictability across three species of batoids caught as by-catch in south-eastern Australia. Stable isotope analysis of 24 mothers and their litters revealed that isotope ratios of embryos were significantly different from their corresponding mothers and that the scale and direction of the difference varied within and across species. The range of variation across species was 3.5‰ for δ¹³C and 4‰ for δ¹⁵N, equivalent to a difference in trophic level. In one species (Urolophus paucimaculatus) litters could be significantly enriched or depleted in ¹³C and ¹⁵N relative to their mothers' isotope signatures. These results suggest that patterns of mother-embryo isotope fractionation vary within and between species and that these patterns may not be explained only by developmental mode. Contrasting patterns of fractionation between and within species make it difficult to adjust mother-embryo fractionation with broad-scale correction factors.