Surviving Predation : multi - species grouping is a defense strategy for 3 sympatric Batoids in Heron Island , Australia

Multi-species groups are potentially mutualistic interactions that have garnered relatively little scientific attention. This study examines three batoids (skates and rays), Dasyatis thetidis, Pastinachus sephen, and Rhinobatos typus that regularly form resting aggregations in the intertidal sand flats of Heron Island, Australia. The defensive role of these aggregations is assessed with the aim of evaluating two questions. 1: How does predation risk affect the decision to form groups? And 2: Are mixed species groups more advantageous than single species groups? All three species responded to increased predation risk as represented by either a smaller body size or by higher tidal height by forming larger and more numerous groups. In addition, all three species showed a significant preference for mixed species groups over single species groups. This data strongly suggests that resting aggregations serve a defensive purpose, and that this may be a novel example of mutualism between batoids.