The low-frequency songs of fin and blue whales seem to be love ballads rather than navigational signals, scientists say.

Researchers used underwater microphones to record whale songs in the Pacific Ocean off Mexico's Baja Peninsula. They found it was only the males who were singing and concluded the sea creatures were probably trying to attract mates.

Unlike some other whales, fin and blue whales don't congregate in breeding areas to mate. Their low-frequency calls can travel long distances and would help in finding a mate, the researchers say.

Fin whales can grow up to 26 metresCourtesy Bernie Tershey, University of California, Santa Cruz

Scientists from the University of California-Santa Cruz, Cornell University, Mexico's Universidad Autónoma de Baja California Sur and the California Academy of Sciences were able to pinpoint which whales were singing.

Other researchers had suggested the calls were sonar-like signals that helped the whales to find their way.

"We hypothesize that whale songs evolved to take advantage of the ocean's sound channel, especially for some of their most important kinds of communication, including finding a mate," said Cornell University bioacoustics researcher Christopher Clark, one of the study's co-authors.

If the sounds are in fact mating calls then the researchers say sound waves from sonar on military and commercial ships could be drowning out the whale calls and hampering their breeding encounters.

The study appears in Thursday's issue of the journal Nature.