Sharks are just fish. They have no sense of right and wrong the way we see it. They are completely amoral creatures. They kill to eat. They eat to survive. All good really.
Dolphins are self aware. Self awareness is the foundation of theory of mind, which means it is possible that dolphins actually know they inflict pain when they do. Dolphins sometimes "play" with other animals until that animal dies.
Who's the good guy here.. really?