NARAIL , Bangladesh - Swimming in circles alongside a fishing boat, the excited cries of two short-haired otters ring out across a river in southern Bangladesh that feeds into the Sundarbans, the world's largest mangrove forest.
The fishermen lower a net into the water close to the banks of the river, and one by one, tails up, the animals dive under the water with a splash.
It is a rare technique that relies on coordination between man and trained otters, a centuries-old fishing partnership that has already long died out in other parts of Asia.
"Our job depends on the otters," says Shashudhar Biswas, a fisherman in his 50s, whose family has trained the animals to help them fish for generations. The otters do not catch the fish themselves, instead they chase them towards the fishing net placed next to the boat.
"The otters manage to spot fish among the plants, then the fish swim away and we stay close with our nets. If we did it without them, we wouldn't be able to catch as many fish," says Shashudhar's son Vipul, standing as he steers the boat along the leafy canal.
Fishing is usually done during the night when the fishermen can expect to catch between four and 12 kilogrammes (8.8 and 26 pounds) of fish, shrimp and crabs.
The family earns around 250 dollars a month selling their catch at the local market.
But in recent years, once abundant fish are increasingly scarce and when they drag up the nets they are often empty.