Overcoming multi-year impacts of maternal isotope signatures using multi-tracers and fast turnover tissues in juvenile sharks

Stable isotopes are often used to determine the ecological role of different age classes of animals, but particularly for young animals this approach may be compromised. During gestation and or incubation body tissues of the young are derived directly from the mother. In neonates or post hatching, there is a period of transformation as the young grow and forage independently, but during this period different organs will continue to reflect the maternal isotopic signature as a function of their turnover rate. How long this maternal hangover persists remains poorly understood. We applied a multi-tracer approach (delta N-15, delta C-13 and delta S-34) to stable isotope signatures in juvenile bull sharks (Carcharhinus leucas) up to 6.5 years post parturition. We found that maternal provisioning was detectable for up to 3.5 years after birth in muscle but only detectable in young-of-the-year for liver. Inclusion of sulphur revealed when maternal signatures disappeared from low-turnover tissue, while also identifying the spatial and trophic ecology patterns from fast-turnover tissue. These results reveal the importance of sampling fast turnover tissues to study the trophic ecology of juvenile elasmobranchs, and how the use of only delta N-15 and delta C-13 isotopes is likely to make maternal patterns more difficult to detect. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study focused on the detection of maternal provisioning in juvenile bull sharks up to 6.5 years post parturition, with results showing its presence in muscle for up to 3.5 years post birth, but only detectable in young-of-the-year for liver. The inclusion of sulfur helped to reveal when maternal signatures disappeared from low-turnover tissue, while identifying spatial and trophic ecology patterns from fast-turnover tissue. The results emphasize the importance of sampling fast turnover tissues to study the trophic ecology of juvenile elasmobranchs and highlight the challenges of detecting maternal patterns using only delta N-15 and delta C-13 isotopes.