People seem to believe that dolphins are cute and cuddly and innocent, but sharks are cruel and evil and bad. In reality, nature is an amoral place.
For example, do you know that in order to make female dolphins that have recently given birth to be in mating, male dolphins have been known to kill baby dolphins so that the new dolphin mothers would more interested in mating with them? Since female dolphins are spending their time and energy taking care of their new baby, males have been documented to kill baby dolphins to mate.
Dolphins also torture and kill baby sharks, not to protect their offspring, but just for the fun of it.