When people learned he vocalized at a much higher pitch than other whales, they wondered: could other whales hear him? Was he plaintively calling, never hearing a reply? Was he lonely?

The loneliest whale in the world lives in the north Pacific. Scientists have been tracking him on and off for more than 30 years – listening to his vocalizations as he swims back and forth across his patch of ocean, calling into the void and waiting for a reply that never comes. That’s the story, anyway. The makers of a new documentary set out to find the truth – and the whale – but what they discovered is that a whale struggling to be heard may not be that unusual at all.

The tale has its origins in the cold war, when the US military deployed a network of hydrophones across the ocean floor to listen for Soviet submarines. In the process, operators also picked up unexpected background noises, including a series of strange, low-frequency moans initially attributed to an unknown “Jezebel Monster” but later identified as the deep, rumbling calls of blue and fin whales. By the end of the 1980s, with the cold war spluttering to an end, the Pentagon made the network available to whale researchers. Among them was William Watkins, a pioneer in identifying and tracking marine mammals by the sounds they make.