May 1 : Deep beneath the ocean surface, sperm whales swim through the dark waters, clicking to each other in bursts of sound that can travel for kilometres (miles). Now, scientists say they are beginning to follow those exchanges in real time using an autonomous underwater robot that can track whales by listening to their voices.    Sperm whales use clicks to navigate and hunt, and also produce patterned sequences of clicks, known as "codas," that are thought to play a role in communication.