Pygmy blue whale: The ‘small’ blue whale that can grow to 24.1 metres and roams thousands of miles across the Southern Hemisphere

The pygmy blue whale is the smaller of the two recognised blue whale subspecies in the Southern Hemisphere, yet it can still reach about 24.1 metres in length. A 2007 study published in Mammal Review titled ‘Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian Ocean’ examined thousands of records to map where blue whales occur across the Southern Hemisphere and the northern Indian Ocean. The research found that pygmy blue whales occupy a broad range, from the Indian Ocean to southern Australia and New Zealand. Unlike Antarctic blue whales, they are generally found farther north and appear to follow their own seasonal movement patterns. Their smaller size also sets them apart from the Antarctic subspecies, which can exceed 30 metres. The study offers a closer look at a whale that may be smaller by name, but remains one of the largest animals on Earth, showing how much can be hidden behind a modest name.The pygmy blue whale can reach 24.1 metres in length, placing it only several metres below the Antarctic blue whale. The researchers compared the two recognised Southern Hemisphere subspecies and found a clear difference in maximum body size. Antarctic blue whales can exceed 30 metres, while pygmy blue whales reach about 24.1 metres. Pygmy blue whales mature at about 19.2 metres, compared with roughly 23.7 metres for Antarctic blue whales. The figures show that ‘pygmy’ refers to its smaller size relative to the Antarctic subspecies, not to a small-bodied whale in absolute terms.The study drew on an unusually large collection of historical and modern records. The researchers examined more than 303,000 catch records, 4,383 sighting records involving at least 8,058 whales, 103 strandings, thousands of discovery marks and acoustic recordings. Together, these records helped researchers identify patterns that would be difficult to see from sightings alone. Pygmy blue whales were found around the Indian Ocean and from southern Australia to New Zealand. The researchers identified at least four broad groupings, including whales in the northern Indian Ocean, from Madagascar to the Subantarctic, around Indonesia and western and southern Australia, and around New Zealand. The study also found that sightings were generally more frequent than those of Antarctic blue whales across several regions.Pygmy blue whales do not remain in one part of the ocean. The research found seasonal movements across regions. In the northern Indian Ocean, whales were recorded around Sri Lanka and India throughout the year, with seasonal records around the Maldives. South of Madagascar, pygmy blue whales spread through the southern Indian Ocean during summer, while acoustic records suggested movement northwards in winter. Around Australia and Indonesia, the pattern was especially clear. Whales were recorded in Indonesian waters from May to November, while concentrations along southern Australia were reported mainly from November to May. These records suggest a clear migratory link between the two regions. The exact routes remain uncertain because the species is difficult to track across vast waters.Pygmy blue whale gathering is closely linked to ocean conditions and food. Researchers found that blue whales generally avoid nutrient-poor central ocean gyres and are more common where phytoplankton levels are high. Areas shaped by upwelling, ocean fronts, and shifting currents can create conditions that support prey. Around Australia and Indonesia, researchers highlighted several such areas, including waters influenced by upwelling. These processes can concentrate food and create productive feeding grounds. The study also noted that pygmy blue whales were often recorded alone or in pairs. Larger aggregations were uncommon in the records. Their movements therefore reflect seasonal patterns and changes in ocean productivity across the wider region.