- Scientists have recorded blue whale songs for the first time in Indian waters off the Lakshadweep islands in the Arabian Sea.
- Their presence in Lakshadweep demonstrates that the waters in this archipelago are rich and productive. Experts say whales singing is a likely signal that the area is a breeding ground for whales for certain parts of the year.
- Unravelling how long the whales spend in Indian waters and other questions can aid science-based management and conservation plans for this climate-vulnerable region.
One hot 2019 afternoon in Lakshadweep, as marine mammal scientist Divya Panicker sat engrossed in listening to recordings retrieved from underwater sound recorders, she came across low blue whale moans, amid a cacophony of a rooster crow.
Panicker described the acoustic experience with the giants as “one of the most thrilling parts” of her study — the first to document blue whale songs in Indian waters in the Lakshadweep archipelago in the Arabian Sea.
She speculates that there were at least two blue whales singing at a time. “The song is made up of three notes and ranges between 30 and 100Hz. I sped up the songs several times to bring them within my hearing. It was quite wacky listening to low blue whale moans with a rooster crowing in the background,” Panicker reminisced.
Analysis of recordings from late 2018 to early 2020 revealed that blue whales were present in Lakshadweep waters during April and May, just before the southwest monsoon season.
“Although we know blue whales occur and are singing in these waters,
we do not know if they are travelling through or feeding in these
waters. One of the next steps is to carry out dedicated visual surveys
in April and May over the next few years to understand their behaviour
and some prey sampling during this period,” Panicker, a doctoral student
in oceanography at the University of Washington, told Mongabay-India.
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| Over a span of 13 months, acoustic recorders were deployed, retrieved for data and changing batteries and redeployed every three months. The reserachers analysed low-frequency bands to look for blue whale vocalisations. Photo by Divya Panicker. |
Because blue whales track productive waters, their presence in Lakshadweep, which is on the cusp of major tourism and infrastructure expansion, demonstrates that the waters in this archipelago are rich and productive.
“The reef, lagoon, island and open ocean are intricately linked and any development and infrastructure plans for the islands need to be carried out within the ecological limits of this fragile ecosystem. It is important to understand their ecology and distributions to draw up a science-based species-specific conservation or management strategy,” adds Panicker.
Marine mammal expert Dipani Sutaria, who studies humpback whales in the Indian waters, said blue whale songs, belted out by males possibly for finding a mate, likely signal that the area is a breeding ground for whales during certain parts of the year.
“All cetaceans (whales, dolphins, and porpoises) use sound to forage (find food), navigate and communicate. Sound travels a little over four times faster in seawater than it does in air, and in the absence of light, cetaceans have evolved perfectly to use sound as a way of seeing. Cetaceans are highly social and baleen whales such as blue whales and humpback whales produce different kinds of vocalisations, some of which can travel thousands of kilometres,” Sutaria said.
“They make high-frequency sounds for locating prey and the other kind of vocalisation is a song; or a repetition of units. Only the males sing in both blues and humpbacks and are considered to be related to mate selection and increasing the opportunity to find mates, a sign of the breeding season. So if you have singing whales in an area at a certain time of the year, it means this area is likely a seasonal breeding ground,” Sutaria told Mongabay-India.
Sutaria’s team found a blue whale singing off the Kerala coast in the Arabian Sea in May 2021. “Our team is trying to explore the presence of humpback whales off the southwest coast of India using passive acoustic monitoring, and in May 2021 we found a blue whale singing (including some foraging calls) from the same ‘acoustic’ population in the Arabian Sea. Our finding fits in with the Lakshadweep observation that blue whales were present/move through the southwestern waters during April and May,’ Sutaria, member of the IUCN Cetacean Specialist Group, added.
Blue whale melodies in the Indian Ocean
Blue whales (Balaenoptera musculus spp.), are an endangered species globally. While Antarctic blue whales (B. m. intermedia), reach up to 30 meters in length and weigh 200 tonnes (approximately 33 elephants), populations of smaller pygmy blue whales, growing up to about 24 metres and weighing roughly half of Antarctic blue whales, are known to occur in the Indian Ocean, the smallest of the major oceans on Earth, but the fastest-warming tropical ocean.
Pygmy blue whales (PBW) are found throughout the Indian Ocean, including the northern Indian Ocean (NIO) and the Arabian Sea.
Blue whale vocalisations offer clues to scientists about the identities of these mammals. Based on their distinct song types, scientists say four possible populations of pygmy blue whales, comprising one or two subspecies to date (B. m. brevicauda and B. m. indica), occur in the Indian Ocean.
The so-called “acoustic populations” of pygmy blue whales (PBW) in the Indian Ocean include the NIO PBW (sometimes referred to as ‘Sri Lanka song’, likely B. m. indica); northwest Indian Ocean; southwest Indian Ocean (sometimes referred to as ‘Australia song’); and southeast Indian Ocean PBW populations (sometimes referred to as ‘Madagascar song’).
The songs recorded in the Lakshadweep waters, says Panicker, were similar to those recorded by Abigail Alling in Sri Lanka in 1980, currently called the northern Indian Ocean blue whale song. These songs have also been heard off the Chagos archipelago (southern end of the mid-oceanic Laccadive-Maldivian-Chagos ridge).
“Usually, blue whales (Balaenoptera musculus spp.), have very consistent song patterns but interestingly in some of our recordings, they were dropping the last unit. This has not been reported for this song type and for future work it would be cool to understand why they may be doing this,” she shared.
The study extends the known range of this song type (northern Indian Ocean blue whale song) a further 1,000 kilometres (620 miles) northwest of Sri Lanka and is particularly significant because Indian waters are a habitat for blue whales but there is very little dedicated research on these animals.
The Lakshadweep research was carried out by the University of Washington in collaboration with the Wildlife Programme at the National Centre for Biological Sciences. On-field dive support was provided by Lakshadweep Scuba Adventures (Anwer Hussein, Syed AbdullaKoya, Amanullah VP, Abdul Raheem PP).
Acoustic recorders were deployed by divers on the reef flats near the underwater slope. Over 13 months, recorders were retrieved and redeployed every three months or so – retrieving the data, changing batteries, and analysing low-frequency bands to look for blue whale vocalisations.
Panicker elaborates that blue whales consume dense patches of prey to grow to these large sizes. “They feed on some of the smallest animals in the ocean – zooplankton and shrimp – which are prey to a whole host of pelagic fishes and mammals. Therefore, studying blue whale distributions gives a glimpse into the most productive and rich habitats in the Arabian Sea that are heavily influenced by monsoonal cycles and a changing climate.”
According to the latest report by the IPCC, the surface of the Indian Ocean has warmed faster than the global average. Globally, anthropogenic warming is very likely to further decrease ocean oxygen concentrations and this deoxygenation is projected to persist for thousands of years, the report warned.
Commercial whaling had nearly wiped out blue whale populations globally in the 20th century and they are only now slowly recovering from these impacts. They are long-lived animals, having one calf at a time with long gestation periods. “The populations in the Arabian Sea were persecuted by whaling ships in the 60s and 70s as well. Some other threats whales face in this densely populated region are ship strikes and a changing climate,” explained Panicker.
For instance, an important blue whale feeding area near Sri Lanka is right next to a major global shipping lane. Deep-sea exploration and mining plans will generate constant noise across vast areas and can also impact blue whale populations.
“We also know from recent studies that there are changes in the monsoon patterns and an intensification of the frequency and duration of cyclones – this is likely to have major impacts on blue whale prey and in turn will affect whales as well,” she said. Usually calmer than the Bay of Bengal, researchers caution the Arabian Sea is getting more active with the rapid intensification of cyclones due to climate change; cyclone Okchi and Tauktae were the most recent ones.
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