Pygmy blue whale
| Pygmy blue whale[1] | |
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| Skeleton at Melbourne Museum | |
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B. m. brevicauda
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| Trinomial name | |
| Balaenoptera musculus brevicauda Ichihara, 1966
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The pygmy blue whale (Balaenoptera musculus brevicauda) is a subspecies of the blue whale (Balaenoptera musculus) found in the Indian Ocean and the southern Pacific Ocean.
Reaching lengths of 24 metres (79 ft) it is smaller than the other commonly recognized subspecies, B. m. musculus and B. m. intermedia, the former reaching 28 m (92 ft) and the latter 30 m (98 ft), hence its common name.[3]
According to observations made since the subspecies was first described in 1966, the pygmy blue whale differs from the "true" blue whales in a number of physical characteristics. It has:
- broader and shorter baleen plates,
- a shorter tail, and hence a proportionately longer body in front of the dorsal fin, and
- a larger head relative to body size.
The shorter tail gives the pygmy blue whale more of a tadpole-like shape, and reflects in differences in diving behaviour: whereas in the "true" blues, there is a delay between the submergence of the dorsal fin and the caudal peduncle; in pygmy blue whales, the dorsal and peduncle submerge simultaneously. Pygmy blue whales also tend to be darker than the other subspecies of blue whales, and the shape of their blowhole is different.[3][4]
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 the Antarctic to feed.[3][5]
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 it could 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.[6]
Pygmy blue whales are believed to be more numerous than the other subspecies. Estimates put their numbers at around 10,000 individuals, whereas the other subspecies combined are estimated to total around 5,000. 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.[5]
Specimens
- MNZ MM002191, collected Motutapu Island, Hauraki Gulf, New Zealand, September 1994.
Conservation status
The pygmy blue whale is covered by the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MOU)
References
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