δ¹³C, δ¹⁵N, and δ³⁴S isotope values from preserved elasmobranch jaws: Implications for ecological studies from existing collections

Stable isotope analysis has become a widely used biogeochemical tool owing to its capacity to reveal predator foraging habitats, trophic level, and prey preferences. The breadth of applicable tissue types is quickly growing across taxa, including for elasmobranchs, with tooth isotopes gaining traction to trace within-individual variation in trophic ecology. Jaws in museums and private collections present a unique opportunity to access samples from rare or protected species and size classes. However, most of these jaws are chemically treated to prevent degradation and to whiten teeth and cartilage for aesthetic and long-term display. Prior to using stable isotopes from these jaws, we need to understand the impacts of chemical treatments on carbon, nitrogen, and sulphur isotopes. We compared the tooth preparation process (acid digestion) and δ¹⁵N, δ¹³C, and δ³⁴S values of teeth from dried jaws to jaws preserved in ethanol, bleach, or hydrogen peroxide. We investigated the effects of preservation methods across three elasmobranch species with distinct tooth morphologies: cownose rays (Rhinoptera bonasus) with tooth plates, gummy sharks (Mustelus antarcticus) with small plate-like teeth, and broadnose sevengill sharks (Notorynchus cepedianus) with larger serrated teeth. Preservation had no impact on tooth digestibility or δ¹⁵N, δ¹³C, and δ³⁴S values across all dentition types. These findings support the use of display jaws from private collections and museums in ecological studies using isotopes.