A previously unsuspected second population of blue whales has been identified in the Indian Ocean from their unfamiliar song patterns.
Their distinctive sounds were recorded at three locations more than 2000 miles apart, starting in 2017 off Madagascar, then further north off Oman in the Arabian Sea as well as in the Chagos Archipelago in the middle of the ocean. The scientists who made the recordings have just published their study.
Until now the Indian Ocean had been thought to harbour only a single population of blue whales – those encountered by some fortunate scuba divers in the past off Sri Lanka. But although all blue whale song is characterised by regularly spaced-out low-frequency repetitions of one phrase, the two sets of sounds didn’t match up.
Even without visual or genetic data, the scientists studying the audio recordings are confident that there are at least two distinct populations of Balaenoptera musculus in the Indian Ocean, while pointing out that there might be some overlapping between the two.
Soon after the recordings were taken off the Omani coast, blue whales were sighted in the vicinity. Blue whale song had never before been identified in the western Arabian Sea.
The timing of the whales’ presence there suggested that intensive illegal Soviet whaling that saw 1294 blue whales killed in the 1960s had targeted this population rather than, as previously assumed, the more widely distributed “Sri Lanka” population.