Summarising 40 years of gastric lavage studies to evaluate efficiency and survival in sharks and rays.

Traditionally, lethal stomach dissection has been used to study the diets of sharks and rays, but conservation and animal welfare concerns necessitate non-lethal alternatives, such as gastric lavage (stomach or gut flushing). In this study, we summarised gastric lavage studies on elasmobranchs to identify which species/groups it has been effective for, the difficulties encountered and if post-release survival has been evaluated. Secondly, we used a field study to (1) demonstrate how to perform gastric lavage on juvenile rays, (2) assess its effectiveness and (3) verify post-release survival using mark-recapture techniques. Only 23 published studies have used gastric lavage on either sharks or rays, indicating that this technique is still highly underutilised in ecological research. Effectiveness at obtaining stomach contents varied but often exceeded 50%, particularly for rays. Captivity studies provided greater evidence of survival than field studies, and only one field study assessed long-term survival using tag-recapture methods. In this field study, gastric lavage was highly effective for young juvenile rays, and recaptures verified survival for various periods after release. More research is needed to adapt gastric lavage across a wider range of species and sizes, especially larger sharks. Furthermore, incorporating approaches to validate survival following non-lethal handling procedures will be essential to ensure ethical compliance and optimal outcomes for research and conservation.