Zinc isotopes in muscle tissues as a novel niche tracer for elasmobranchs: a proof-of-concept study

Stable zinc isotopes (δ⁶⁶Zn) have recently emerged as promising ecological tracers, yet their application in elasmobranchs remains limited. Here, we evaluated the use of δ⁶⁶Zn in elasmobranch muscle tissue in combination with traditional isotopes (δ¹³C and δ¹⁵N) to compare isotopic variability among three sympatric stingray species inhabiting a heterogeneous coastal system along the Brazilian coast. The analyses revealed species-specific δ⁶⁶Zn patterns and differences in multitracer isotopic space among species. Hypanus guttatus exhibited broader isotopic variability than Hypanus marianae and Hypanus berthalutzae, which showed more constrained and partially overlapping isotopic patterns. Compared with δ¹³C and δ¹⁵N, δ⁶⁶Zn exhibited partially distinct isotopic behaviour, suggesting sensitivity to a more complex combination of trophic, environmental, and physiological influences. This additional isotopic variability contributed complementary information to species discrimination. Overall, our results suggest that Zn isotopes in soft tissues represent a promising addition to multitracer isotopic approaches in marine predators.