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Though 52 Hertz has never been seen many have heard his watery love songs, recorded by scientists and US navy sonar detectors.

"I receive letters, emails and poems - mostly from women - and it's heartbreaking to read some of the things they say. They identify with this animal who doesn't seem to fit in anywhere, doesn't make friends easily, feels alone and feels different from everybody."

For many lovelorn humans 52 Hertz has come to symbolise the hopeless romantic in us all. "It's very sad that so many people identify with this whale," says marine biologist Mary Ann Daher of the Woods Hole Oceanographic Institution in Massachusetts, who co-authored the original research on the discovery of 52 Hertz.

But although he swims in waters that are populated by thousands of other whales no female ever responds because his voice is unusually high for a whale - about 52 Hertz - which is what researchers have named him.

He cries out in long, low moans, his musical mating calls ringing for hours through the darkness of the deepest seas. His strong voice carries for miles through the briny, broadcasting a wide repertory of heartfelt tunes.

The subject of a documentary currently being filmed, the lovelorn mammal has been tracked by scientists since 1989 as he migrates up and down the world's largest ocean along the Pacific north-west coast of North America.

He is a lone voice crying out for love in the wilderness. For years he has roamed singing unrequited songs of yearning, searching for a soul to share his solitary world. His plaintive love songs have been heard by many yet he has never been seen. He is the loneliest whale in the world.

People identify with this animal who doesn't seem to fit in anywhere, doesn't make friends easily, feels alone and feels different from everybody

The leviathan's voice, at 52 Hertz, would sound deep to a human, similar to the lowest note on a tuba, yet is extremely high-pitched compared with most large whales, like playing a piccolo at a Harley-Davidson rally.

rEGULAR blue and fin whales sing at about 15 to 20 Hertz: a bone-shaking low-bass rumble below the range of normal human hearing. Even if 52 Hertz is a firm-bodied, sizzlingly sexy macho male it is apparently hard to attract the opposite sex with a high-pitched voice.

Scientists are not even certain what type of whale he is or whether he might be an unknown species on a futile quest for an equally elusive mate. His calls are shorter but more frequent than other whales, as if he speaks a language that is all his own.

"We don't know whether he sounds that way because he's a hybrid of a blue whale and a fin whale or if he's a blue whale with a physical deformity that causes him to sing at 52 Hertz," says Daher.

Blue whales are the largest creatures on the planet, growing up to almost 100 feet and living for up to 80 years. There were about 12,000 blue whales roaming the world's oceans in 2002 and with a current ban on their hunting the population is believed to have increased. Yet 52 Hertz's falsetto mating calls are left unanswered as he wanders the vast Pacific in search not only of love but also of food, pursuing clouds of plankton and tiny shrimp-like krill. Scientists believe he is a baleen whale, a broad sub-order of marine mammal which includes 15 species of whales without teeth, filtering food through giant, brush-like plates in his mouth. Baleen whales lack sharp eyesight and a keen sense of smell underwater. Instead they use sound to help to attract mates, to recognise each other, to socialise and probably to navigate.

Yet it is his distinctive solitary voice, never heard accompanied by another whale, that has allowed scientists to track 52 Hertz so closely. William Watkins of the Woods Hole Oceanographic Institution, who invented the first underwater recording system, first heard 52 Hertz's unique highpitched song back in 1989 when he was studying the mating calls of male whales, which are far more vocal than the females.

The US navy's sophisticated billion-dollar hydrophone system, designed to track Soviet nuclear submarines during the Cold War, recorded his migratory patterns in great detail each year, cruising from central California to the Aleutian Islands in the north Pacific. He always travels solo, "unrelated to the presence or movement of other whale species", according to the original report in Deep Sea Journal. He swims up to 42 miles a day and one year covered more than 6,873 miles.

However the defence department only releases data days after 52 Hertz has moved on, too late for scientists to dispatch vessels to meet him in person. Unsurprisingly the cash-strapped US navy has little interest in pursuing a solitary love-sick whale.

Some scientists speculate that he is a linguistic hybrid, the marine equivalent of a Cockney in Scotland: possibly a blue whale from the Atlantic with a local dialect very different from that of Pacific blue whales. "When you get into their social sounds that's where you get this mixture of loudness and the structures are very context-dependent," says bioacoustics researcher Christopher Clark of Cornell University in New York.

Although he may be lonely in the ocean 52 Hertz has won many landbound admirers whose interest has helped to promote greater study of the ocean giants. Numerous deaf people have also written to researchers, wondering if 52 Hertz might share their disability.

While he continues to moan his unrequited songs of romantic longing scientists confess that they cannot know what truly lies in the heart and mind of a whale, no matter how unloved.

"We don't know if he's lonely," says oceanographer Mary Ann Daher. "The supposed emotional yearnings of 52 Hertz say much more about the humans who hear his story than it does about the whale himself."

Tales and tunes making a splash

THE lonely whale's unrelenting dedication to singing love songs in the face of repeated heartbreak has proved an inspiration for several musicians and writers.

• In Germany author Agnieszka Jurek penned the illustrated children's book 52 Hertz Wal.

• In Britain the cetacean gave birth to a hard-rocking song The Loneliest Whale In The World by Huddersfield band Dalmatian Rex and the Eigentones, whose songs coincidentally include Loch Ness.

• American singer Kate Micucci recorded Doreen The Whale about a female whale who meets a male with a high-pitched voice that laments: "I'm a guy who has no honey, I sing too high."

• Laura Ann Bates recorded her mournful song dedicated to 52 Hertz, The Loneliest Creature On Earth and artist Mike Ambs' audio project The Loneliest Mix combines the calls of blue whales.

• Is 52 Hertz ready to reveal himself to the waiting world? Film director Joshua Zeman is pursuing the colossus with a dedication last seen in Ahab's quest for Moby Dick. He is now shooting the documentary Finding 52: The Search For The Loneliest Whale In The World.