Imagine roaming the world's largest ocean year after year alone, calling out with the regularity of a metronome, & hearing no response. Such, apparently, is the situation faced by a solitary whale, species unknown, that has been tracked since 1992 in the North Pacific by a classified array of hydrophones used by the Navy to monitor enemy submarines. The animal is called the 52 hertz whale because it makes a distinctive stream of sounds at around that basso profundo frequency, just above the lowest note on a tuba. Its sonic signature is clearly that of a whale, but nothing like the normal voice of the giant blue or the next biggest species, the fin, or any other whale for that matter, said Mary Ann Daher, a marine biologist at the Woods Hole Oceanographic Institution on Cape Cod. Ms. Daher is part of a team built by Dr. William A. Watkins, a pioneer in marine mammal acoustics who died in September, that has spent years trying to eavesdrop on the largely hidden lives of whales. In the current edition of the journal Deep-Sea Research, members of this team report that all signs are that the sounds come from a single animal, whose movements "appeared to be unrelated to the presence or movement of other whale species." The 52 hertz whale may be maturing, since its voice has deepened slightly over time, Ms. Daher said. A gallery of sounds, including the call of 52 hertz, can be heard at www.pmel.noaa.gov/vents/acoustics/spectrograms.html. Team members & other experts have proposed a host of explanations for the whale sounds, among them that the animal is malformed or, most likely, is a hybrid of a blue whale & another species. Ms. Daher said that as word of the paper has spread, she has gotten a host of e-mail messages, some from whale lovers lamenting the notion of a lonely heart of the cetacean world. Some messages have come from deaf people speculating that the whale might share their disability. Dr. Kate Stafford, a researcher at the National Marine Mammal Laboratory in Seattle, said there were reasons to believe that the whale was healthy. "The fact that this individual has been capable of existing in that harsh environment for at least these 12 years indicates there is nothing wrong with it," she said. But she agreed that there was something poignant about the finding. "He's saying, 'Hey I'm out here,' " she said. "Well, nobody is phoning home." by Andrew Revkin