The arrangement is old and locally specific. A fisher taps a wooden pin against the gunwale or calls, and dolphins working the stretch move in, encircling a shoal and pressing it towards the boat. A rolling dive or a tail movement signals the moment to throw a cast net. Fish disoriented by the net become easier for the dolphins to catch as well.
The partnership is documented from the nineteenth century onwards and involves particular dolphins and particular fishing families along known reaches of the river. Similar cooperative fishing exists between people and bottlenose dolphins at Laguna in Brazil, but such relationships are rare worldwide.
The practice is disappearing with the dolphins. The Ayeyarwady subpopulation has been counted in the dozens, and electrofishing, gillnets and mercury from gold mining are the principal pressures. The number of fishers who still work with dolphins has fallen alongside them.