Repeated Observations Suggesting Kleptoparasitism by a Common Bottlenose Dolphin (Tursiops truncatus) on the Great...

Kleptoparasitism, the deliberate theft of food from other animals, is a widespread but usually facultative foraging tactic used by many taxa. It has rarely been documented in aquatic species, particularly marine mammals. Here, we present observational evidence of kleptoparasitism initiated by a free-ranging Common Bottlenose Dolphin (Tursiops truncatus) at Lady Elliot Island in the southern Great Barrier Reef, Australia. Between 2021 and 2025, opportunistic underwater observations and video recordings documented 11 kleptoparasitic interactions in which an individual dolphin targeted specific Bigeye Trevally (Caranx sexfasciatus), pursued them until regurgitation occurred, and consumed the expelled prey or prey remains while the trevally swam away. Using photo-identification, all observations were confirmed to involve the same individual dolphin. The dolphin produced intense echolocation click trains and low-frequency tonal sounds (LFTS, mean duration = 0.88 ± 0.51 s, range = 0.36-2.14 s). Based on video samples analysed, following pursuit and the production of clicks and LFTS, the trevally systematically regurgitated its prey, which was subsequently consumed by the dolphin. These observations represent the first detailed description of kleptoparasitism in cetaceans, and we speculate that induced regurgitation may function as an energetically efficient alternative to independent predation. The findings highlight the behavioural plasticity of delphinids and underscore the likelihood that rare or novel foraging tactics in cetaceans remain underreported due to observational limitations.