The two men killed, Sunder Raj, 48, and Pandit Tiwari, 52, were fishing illegally for mud crabs off North Sentinel Island, a speck of land in the Andaman and Nicobar Islands archipelago.
During the night their anchor, a rock tied to a rope, failed to hold their open-topped boat against the currents and they drifted towards the island.
"As day broke, fellow fishermen say they tried to shout at the men and warn them they were in danger," said Samir Acharya, the head of the Society for Andaman and Nicobar Ecology, an environmental organisation.
"However they did not respond - they were probably drunk - and the boat drifted into the shallows where they were attacked and killed."