Weighing up to 380,000 pounds and stretching 100 feet long, the blue whale Balaenoptera musculus)—the largest creature to have ever lived on Earth—might at first seem difficult for human eyes and ears to miss. But despite its size and worldwide distribution this species became endangered due to twentieth century whaling. Its not hard to imagine why whales might wish to remain relatively anonymous based on human's past history with the leviathans.
A previously unknown population of the giants has been revealed that has long been lurking in the Indian Ocean, new research suggests. Blue whales in the Indian Ocean are currently thought to represent 2 or 3 subspecies (Balaenoptera musculus intermedia, B. m. brevicauda, B. m. indica), believed to be structured into 4 populations, each with a diagnostic (distinctive) song-type. See The Society for Marine Mammalogy for the complete list.
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The covert cadre of whales, described in the Endangered Species Research paper, A new blue whale song-type described for the Arabian Sea and Western Indian Ocean, Cerchio et. al. describe a previously unreported song-type and posit that the new discovery implies the probable existence of a population that has been undetected or conflated with another population. The novel song-type was recorded off Oman in the northern Indian Ocean/Arabian Sea, off the western Chagos Archipelago in the equatorial central Indian Ocean, and off Madagascar in the southwestern Indian Ocean.
The song these whales sing is described as a slow, bellowing ballad that's distinct from any other whale song ever described. It joins only a dozen or so other blue whale songs that have been documented, each the calling card of a unique population.
Lead author Salvatore Cerchio, a marine mammal biologist at the African Aquatic Conservation Fund in Massachusetts describes the song as "like hearing different songs within a genre—Stevie Ray Vaughan versus B. B. King, . . . It's all blues, but you know the different styles."
Because this is the only blue whale song that has been identified in the western Arabian Sea, the researchers label it the ‘Northwest Indian Ocean’ song-type to distinguish it from other regional song-types.
This find is a reminder that our oceans are still a very unexplored place.
Their new research found spatiotemporal variation that suggested a distribution west of 70°E, with potential affinity for the northern Indian Ocean/Arabian Sea, and only minor presence in the southwestern Indian Ocean.
Dr. Cerchio and his colleagues first tuned into the whales' newfound song while in scientific pursuit of a pod of Omura's whales off the coast of Madagascar several years ago. After hearing the rumblings of blue whales via a recorder planted on the coastal shelf, the researchers decided to drop their instruments into deeper water in the hopes of eavesdropping further. Dr. Cerchio said, "if you put a hydrophone somewhere no one has put a hydrophone before, you're going to discover something."
The timing of presence off Oman suggested that intensive illegal Soviet whaling that took 1294 blue whales in the 1960s likely targeted this population, as opposed to the more widely distributed ‘Sri Lanka’ acoustic population as previously assumed. Based upon geographic distribution and potential aseasonal reproduction found in the Soviet catch data, the researchers suggest that if there is a northern Indian Ocean subspecies (B. m. indica), it is likely this population.
A number of blue whale populations each with its own characteristic song, have long been known to visit this pocket of the Indian ocean. Partnerships with other researchers revealed that the distinctive calls had been detected at another recording out post off the coast of Oman, in the Arabian Sea, where the sounds seem particular prevalent. Another windfall came in 2018 when Dr. Cerchio learned that colleagues in Australia had heard the whales crooning the same song in the central Indian Ocean near the Chagos Archipelago.
Data compiled from the three sites, each separated by hundreds or thousands of miles, painted a rough portrait of a pod of whales trawling about in the Indian Ocean's northwest and perhaps beyond.
The researchers ruled out the possibility that the songs could be attributed to other species of whales. And side-by-side comparisons of the new blue whale tune with others showed convincingly that the northwestern Indian Ocean variety was distinct.
Genetic samples would seal this oceanic mystery but blue whales, which spend most of their lives far from shore, are difficult to study. Whaling in the 19th and 20th centuries also killed hundreds of thousands of whales; an estimated 10,000 to 25,000 blue whales are thought to remain.
Not much is known about blue whale songs although most researchers think that they help males woo their mates, as is the case with closely-related species. That can make any modifications to a whale melody fairly important biologically. If two populations cannot talk to each other over time, they're going to grow apart.
Eventually, populations with different takes on a tune might splinter into subspecies, with their own behaviors and quirks. There's not yet evidence to show that has happened with these blue whales, nor much information on what might have driven them from their southerly cousins. But even if the whales in the new group don't yet formally occupy a new branch on the tree of life, they are worth getting to know.
What this discovery shows us is that there are different populations, with different adaptations, with potentially different needs. Moreover, the potentially restricted range, intensive historic whaling, and the fact that the song-type has been previously undetected, suggests a small population that is in critical need of status assessment and conservation action.
Short answer: Whale gigantism is tied closely to two things, 1. their choice of prey, and 2. the coincidence of their evolution with a global increase in the upwelling of nutrient-rich water from the depths of the ocean.
The ocean is a vast, open space, so to communicate underwater, its best that your message travels far. . . and sound travels four times faster in water than in air, so many animals use this to their advantage.
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