Authorities classify the species into three or four subspecies: "B. m. musculus", the northern blue whale consisting of the North Atlantic and North Pacific populations, "B. m. intermedia", the southern blue whale of the Southern Ocean, "B. m. brevicauda", the pygmy blue whale found in the Indian Ocean and South Pacific, and the more problematic "B. m. indica", the great Indian rorqual, which is also found in the Indian Ocean and, although described earlier, may be the same subspecies as "B. m. brevicauda".