The pygmy blue whale is a subspecies of the blue whale found in the Indian Ocean and the southern Pacific Ocean. Reaching lengths of up to 24 metres it is smaller than the other commonly recognized subspecies, B. m. musculus and B. m. intermedia, the former reaching 28 m and the latter 30 m, hence its common name. The pygmy blue whale is the only one of the three identifiable subspecies to be found regularly in tropical waters. It occurs from the sub-Antarctic zone to the southern Indian Ocean and southwestern Pacific Ocean, breeding in the Indian and South Atlantic oceans, and travelling south to above the Antarctic to feed, although they very rarely cross the Antarctic Convergence. A fourth subspecies, B. m. indica, was identified by Blyth in 1859 in the northern Indian Ocean, but difficulties in identifying distinguishing features for this subspecies lead to it being used a synonym for B. m. musculus. It is now thought to be the same subspecies as the pygmy blue whale. Records for Soviet catches seem to indicate the female adult size is closer to that of the pygmy blue than B. m. musculus, although the populations of B. m. indica and B. m. brevicauda appear to be discrete, and the breeding seasons differ by almost six months. Pygmy blue whales are believed to be more numerous than the other subspecies, possibly making up half of all blue whales alive today. Although the designation is widely accepted, because of the relatively healthy stocks of pygmy blues compared to the other subspecies, The Committee on the Status of Endangered Wildlife in Canada has questioned whether the subclassification of the pygmy blue whale has been driven by the interests of the whaling industry.
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