Back in 2009, when a team of researchers and scientists were collecting data for a study in the southern coastal districts of Bangladesh, they hit upon something quite bizarre. Local fishermen said a large number of their colleagues were languishing in Indian prisons.

When the researchers checked the facts, they found that no less than 20,000 Bangladeshi fishermen were indeed incarcerated in the South Indian state of Andhra Pradesh. Most of the fishermen had landed there in the last three-four years.

The answer is unequivocal: their fishing boats sank in rough waves at sea.

"This was it: the waves – huge, strong and unexpected – were the culprits. The fishermen were facing a turbulent sea," said Ahsan Uddin Ahmed, a scientist who was part of the research team. "We double-checked the data and found a very strange thing unfolding: the sea, hitherto familiar to the experienced fishermen, was behaving quite differently. More and more fishing boats were sinking in turbulent waters while fishing in the deep sea. The lucky ones landed on unknown shores."