What is the "52 Hz whale"?

There is a whale, somewhere in the North Pacific, that sings at a frequency its fellows do not use. For more than thirty years, underwater hydrophones have recorded its voice, followed its seasonal movements between California and Alaska, and found that it appears to travel alone. No other cetacean has ever been detected singing at the same frequency. No one has ever seen this animal. It is not known what species it belongs to, nor whether it is one, two or several. Nicknamed “the 52 hertz whale” or “the loneliest whale in the world”, it has become one of the most affecting mysteries of marine bioacoustics. Its story brings together the Cold War, ecology, AI and a little poetry.

The discovery by William Watkins

The story begins in 1989. William A. Watkins, an oceanographer and bioacoustician at the Woods Hole Oceanographic Institution, was examining declassified recordings from the SOSUS array, the hydrophone system the United States Navy had deployed in the Pacific during the Cold War to track Soviet submarines. SOSUS has been opened progressively to civilian research since the late 1980s, offering marine scientists an unprecedented acoustic window onto the oceans.

In the data, Watkins picked out an atypical acoustic signature: songs at 52 hertz, repeated sequences, a temporal profile evoking that of a large whale. The difficulty is that the known whales do not emit at this frequency. North Pacific blue whales sing at around 17-25 Hz. Fin whales at around 20 Hz. No identified species lines up with 52 Hz.

Watkins and his team would track this animal for twelve years. They plotted its seasonal movements: along the west coast of North America, between California in winter and Alaska in summer, over distances of several thousand kilometres. The rhythm and the extent of these movements resemble those of a blue whale or a fin whale on migration. But the animal never joins a known group. It sings alone. No one answers it.

Why “the loneliest”?

The nickname “loneliest whale in the world” appeared in the press in the early 2000s, after the publication of Watkins’s major study in 2004 in Deep-Sea Research. The idea is that no other animal uses its frequency, so that in principle its fellows can neither recognise it nor answer it. It would be condemned to total social isolation, an acoustic solitary in a crowded ocean.

This narrative touched the public deeply. The American journalist Andrew Revkin wrote a widely noticed article in the New York Times in 2004. Singers have written songs. A documentary entitled The Loneliest Whale: The Search for 52 was filmed in 2015 and released in 2021. The animal has become a symbol of modern loneliness and of being misunderstood in our noisy societies, a projection probably excessive onto what remains a biological mystery.

But is it really alone?

Several elements complicate this romantic narrative. First, the frequency has fallen slightly over the years: from 52 Hz initially to about 49 Hz in 2010. This decline is consistent with what is observed in blue whales as they age and grow, lower songs corresponding to larger individuals.

Then, in 2010, John Hildebrand and John Calambokidis suggested that there could be more than one individual. Several spaced hydrophones picked up signals at this frequency simultaneously at points too far apart for a single animal to have been at both. If that reading is correct, the “loneliest whale” may not be so alone, but rather a small marginal population sharing an acoustic peculiarity.

Finally, there is no idea of what the animal itself perceives. Perhaps it hears its ordinary fellows perfectly well. Perhaps it communicates with them through other signals that have not been identified. Perhaps its “loneliness” is a human projection onto a biological phenomenon that is not understood.

The scientific hypotheses

Four hypotheses coexist in the literature. The first, and the most popular, is that it would be a hybrid between a blue whale and a fin whale. Such hybrids exist; they are rare but documented. Their songs could be intermediate between those of the two parent species, which would account both for the atypical frequency and for the profile resembling a large whale.

The second hypothesis is that of an anatomical malformation. A peculiarity of the larynx, of the nasal air sacs or of the vocal structures could produce an atypical song in an individual from an ordinary species. If that is the case, the animal is not socially isolated, merely “acoustically malformed”.

The third is that it would be an atypical individual of an existing species, with an aberrant dialect, the human equivalent of a person speaking a very rare variant of a known language. This hypothesis is compatible with the possibility of several individuals.

The fourth hypothesis, the most spectacular and the least likely, is that it would be an undescribed species. This is extremely improbable: modern acoustic surveys cover the Pacific broadly, and an unknown species of large whale would have been picked up by other means (strandings, visual sightings). But science remains theoretically open to the possibility.

The mystery persists

In 2015 the director Joshua Zeman launched an expedition funded in part by Leonardo DiCaprio: The Loneliest Whale Project. For several weeks the team criss-crossed the north-eastern Pacific with hydrophones and visual observers. They recorded a few signals at the right frequency, but never managed to locate the animal and observe it visually. No genetic sample. No image. The documentary that came out of it in 2021 is more a meditation on the mystery than a resolution.

Perhaps we shall never know. The 52 Hz whale, or the 52 Hz whales, go on singing somewhere in the North Pacific. Their recordings are detected regularly. Their identity remains, for now, one of the finest mysteries the ocean still sets against us.

Sources

• Watkins, W.A., Daher, M.A., George, J.E. & Rodriguez, D. (2004). “Twelve years of tracking 52-Hz whale calls from a unique source in the North Pacific”. Deep-Sea Research I, 51, 1889-1901.
• Revkin, A. (2004). “Song of the sea, a cappella and unanswered”. The New York Times, 21 December 2004.
• Hildebrand, J. & Calambokidis, J. (2010). NOAA communications on the possibility of several individuals.
• Zeman, J. (dir.) (2021). The Loneliest Whale: The Search for 52, documentary.
• NOAA, SOSUS / Pacific Marine Environmental Laboratory archives.

---

Going further