A related question is why orcas ("killer whales") don't seem interested in attacking humans as much as you would expect, since they *do* eat mammals. I expect this is more related to how infrequently people swim with them. read more
Dolphins are smart, and generally sociable creatures. They have learned how net-fishing works, and they assist humans with it. It's beneficial for the Dolphins, because the fish that manage to escape the nets are essentially "trapped" and the Dolphins get an easy meal. For centuries, Dolphins have hung around humans and their boats. read more