The excited cries of two short-haired otters, swimming in circles alongside a fishing boat, 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 long died out in other parts of Asia.
"Our job depends on the otters," Mr Shashudhar Biswas told AFP. A fisherman in his 50s, his 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," said Mr 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 4kg and 12kg of fish, shrimp and crabs.
The family earns about 19,450 Bangladesh taka (S$320) a month by selling its catch at the local market.
But once abundant fish have become increasingly scarce in recent years. When the family drags up the nets, they are often empty.
Natural fish populations have reduced drastically in recent years, said Mohammed Mostafa Feeroz, a zoology professor at Dhaka's Jahangirnagar University, because "the fish simply cannot breed".
Mr Feeroz has been studying otter fishing in Bangladesh for 25 years and over this period, the number of families involved has dropped from 500 to just 150.
Mr Vipul worries that his only source of income will soon no longer be profitable. He said: "If there are no fish, then there's no point in having the otter fishing system."
Each month, almost half of his earnings are spent on feeding his five otters - two fully trained adults and three young apprentices - who consume 3kg to 4kg of fish a day.
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