The mullet fishery on the Lagoa do Imaruí lagoon in Laguna involves something genuinely remarkable: a population of wild boto dolphins (Tursiops truncatus gephyreus, the Lahille's bottlenose dolphin) that actively cooperate with fishermen to catch fish. Between April and July, when mullet schools move through the lagoon, the dolphins herd the fish toward shore. At a precise moment — signalled by a distinctive downward dive or tail slap — the fishermen cast their nets in synchrony with the dolphins' movements. The dolphins benefit from the disoriented fish that escape the net; the fishermen catch far more than they could alone.
The lagoon at Barranceira, on the southern shore of the Lagoa do Imaruí, is the best place to watch the interaction. Local guides can take you out by small boat in the right season, and the dolphins are often visible close to shore. There are no guaranteed sightings — it is a natural behaviour, not a performance — but the chances during peak mullet season (May to June) are good.