1. They have been reported to exist in Australia, India, Mauritania, Burma, and the Mediterranean, but the best known are in Brazil.
2. In parts of southern Brazil, human fisherman have been cooperating with dolphins for many generations (of each species).
3. If fishermen clap just the right way, dolphins will herd fish into the desired areas of fishermen, in muddy lagoon areas.
4. The dolphins perform a distinctive kind of dive to signal to the humans it is time to cast the net for the fish.
5. Only some individual dolphins are able (willing?) to do this well, perhaps the others belong to the forty-seven percent.
5b. The dolphins which cooperate with the fisherman are also more social, more socially connected, and more cooperative with other dolphins.
6. The Brazilian fishermen name the star cooperating dolphins after ex-presidents, soccer players, and Hollywood stars.
7. The names aside, it is not clear whether dolphins benefit from offering this assistance; some commentators suggest the dolphins end up with isolated or injured fish from these exercises.
Here is one blog post report on these practices. Here is one piece of the original research. I stumbled upon this while reading the new and excellent Hal Whitehead and Luke Rendell The Cultural Lives of Whales and Dolphins, a new book from University of Chicago Press.