Pygmy Blue Whale
Encyclopedia
The pygmy blue whale 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, which reach 29 m (95 ft) in length, hence its common name.
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:
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.
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.
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.
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.
Blue Whale
The blue whale is a marine mammal belonging to the suborder of baleen whales . At in length and or more in weight, it is the largest known animal to have ever existed....
(Balaenoptera musculus) found in the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and the southern Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
.
Reaching lengths of 24 metres (79 ft) it is smaller than the other commonly recognized subspecies, B. m. musculus and B. m. intermedia, which reach 29 m (95 ft) in length, hence its common name.
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
Tadpole
A tadpole or polliwog is the wholly aquatic larval stage in the life cycle of an amphibian, particularly that of a frog or toad.- Appellation :...
-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
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
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.
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.
A fourth subspecies, B. m. indica, was identified by Blyth
Edward Blyth
Edward Blyth was an English zoologist and pharmacist. He was one of the founders of zoology in India....
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.
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
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
has questioned whether the subclassification of the pygmy blue whale has been driven by the interests of the whaling industry.
Specimens
- MNZ MM002191, collected Motutapu Island, Hauraki Gulf, New Zealand, September 1994.