Sonic waves from warships — Indian and of neighbouring countries — might have killed 40 whales, whose carcasses were found on the Andaman coast, in October 2012, scientists have said. “The low-frequency active sonar (Sound Navigation and Ranging), used by the navy to detect enemy submarines, is the loudest sound ever put into the sea,” C Raghunathan, senior scientist with the Zoological Survey of India in Port Blair, said. “At amplitude of 240 decibels, they are loud enough to kill whales and dolphins.”

In humans, long or repeated exposure to sounds at or above 85 decibels can cause hearing loss.

K Venkataraman, director of ZSI in Kolkata, said, “The sonic waves from warships might have caused the stranding of the whales (in shallow waters).” He added that similar incidents had been reported from the Bahamas, where the US navy conducts its exercises.

Avijit Mitra, former head of the marine science department of Calcutta University, said, “Sonic waves from warships can burst the thin membranes of a whale’s swim bladder, which it uses to maintain buoyancy.”

The Andaman and Nicobar Command (ANC) — the unified command of the Indian armed forces and coast guard — however, was sceptical. “I am not sure if sonic waves have any effect on marine life,” said its spokesperson.

On October 22, fishermen  found 40 dead pilot whales in Elizabeth Bay in Andaman.