Sharks are not necessarily afraid of dolphins. Nor are dolphins often found killing or attacking sharks. There have been a few instances where a dolphin has taken on a shark that is relatively small in order to defend itself. Rumor has it that the myth that sharks are afraid of dolphins may have come from an incident that took place at a seaquarium in the 1950’s when a sandbar shark showed too much interest in the birth of a Bottlenose Dolphin calf, and as a result three of the adult male dolphins ganged up on the shark, butting it in the gills and stomach until it finally died.
During the 1960’s the United States Navy also trained Bottlenose Dolphins to incapacitate large sharks by butting them in their gill pouches. The dolphins quickly learned to attack certain species of sharks such as the Sandbar shark or the Lemon shark but still seemed to be afraid to try and take on a Bull shark. It should be noted that bull sharks are about the same size and shape as the dolphins and that in the wild the Sandbar and Lemon sharks are not typically found to attack dolphins, whereas the Bull shark has been found to attack the dolphins in the wild. This suggests that dolphins may be able to sense which types of sharks pose a threat and which do not.
For the most part sharks and dolphins leave each other alone. However, Some 75% of wild dolphins show some degree of shark scarring, and we usually only see the ones who were fortunate or strong enough to get away.