And In This Corner ...
Q: Do dolphins really beat up sharks?
St. Louis, MO
A: Usually not, unless the shark is relatively small.
This notion is based on a much-publicized incident that took place at the Miami Seaquarium in the 1950's. When a Sandbar Shark showed a bit too much interest in the birth of a Bottlenose Dolphin calf, three of the adult male dolphins ganged up on the shark, butting it in the gills and stomach until it died. This 'protective' behavior was cemented in the public's mind by the television series, Flipper, produced in association with the Miami Seaquarium. There is a record of a Bottlenose Dolphin off California killing a two-foot Leopard Shark (Triakis semifasciata), then supporting it at the surface (which raises doubts about tales of dolphins 'rescuing' human swimmers: perhaps balancing an object on the rostrum is merely a dolphin game, devoid of any altruistic motivation).
During the 1960's, the U.S. Navy trained Bottlenose Dolphins to incapacitate large sharks by butting their delicate gill pouches. The dolphins quickly learned to attack Sandbar (Carcharhinus plumbeus), Lemon (Negaprion brevirostris), and Nurse Sharks (Ginglymostoma cirratum), but refused to approach a Bull Shark (Carcharhinus leucas) of similar size and shape. Sandbar, Lemon, and Nurse Sharks are not known to attack dolphins in the wild, but Bull Sharks are. This suggests that dolphins are able to classify sharks as either dangerous or not dangerous — an eminently practical taxonomy.
In the wild, similar-sized dolphins and sharks pretty much leave each other alone. Some 75% of wild dolphins show some degree of shark scarring — and we usually see only the ones that got away. I have pulled dolphin remains from the stomachs of many sharks over the years, particularly from Tiger Sharks (Galeocerdo cuvier). Thus, it seems that in most battles between dolphins and sharks in the wild, dolphins get the worst of the encounter.