Predator-prey and competitive interactions between sharks (order Selachii) and dolphins (suborder Odontoceti): a review

The importance of interactions between sharks and cetaceans has been a subject of much conjecture, but few studies have addressed these interactions. Sharks (order Selachii) have been hypothesized to be important predators on dolphins and porpoises (suborder Odontoceti). Unfortunately, there are often few data to back up claims that certain shark species are major threats to cetaceans. To help identify potential shark predators in specific locations, available data on interactions with odontocetes for all shark species that may include cetaceans in their diet are reviewed. Shark species are categorized into groups based on predatory interactions with dolphins and porpoises (regular predators, occasional predators, potential predators, ectoparasites and insufficient data). Several shark species that have been overlooked in the cetacean literature are identified as potentially important predators while others that have been suspected to be important predators are probably at most occasional predators. How shark predation can influence dolphin populations, habitat use, group size and behaviour is discussed. How risk of shark predation can vary with habitat attributes in both nearshore and pelagic waters is also discussed. Predator-prey interactions have been the focus of most studies of shark-dolphin interaction, but competitive interactions may also occur. The first analysis of shark-dolphin dietary overlap is presented, which shows it to be significant between common dolphins and several species of sharks, including species that prey upon these dolphins.