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.
The pygmy blue whale[2] formed from a founder group of Antarctic blue whales about 20,000 years ago, around the Last Glacial Maximum. This is likely because blue whales were driven north by expanding ice, and some have stayed there ever since. The pygmy blue whale's recent evolutionary origins cause it to have a relatively low genetic diversity.[3]
Reaching lengths of up to 24m (79ft), it is smaller than the other commonly recognized subspecies, B. m. musculus and B. m. intermedia, the former reaching 28m (92ft) and the latter 30m (98ft) or slightly more, hence its common name.[4]
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.[5]
Pygmy blue whales are believed to be more numerous than the other subspecies, possibly making up half of all blue whales alive today.[6]
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.[7]
Description
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
a larger head relative to body size
a heavier body weight compared to other blue whales of the same length[8]
Pygmy blue whales reach sexual maturity at 10 years of age and a length of 19.2m (63ft), weighing on average 52.5t (51.7 long tons; 57.9 short tons). As adults, males average 21.1m (69ft) and females 21.9m (72ft), with most probably between 20.7 and 22.5m (68 and 74ft).[9] The calculated average weight is 75.5t (74.3 long tons; 83.2 short tons) for males and 90t (89 long tons; 99 short tons) for females. A whale at the maximum known size of 24m (79ft) would weigh in the range of 129.5t (127.5 long tons; 142.7 short tons).[10]
The shorter tail gives the pygmy blue whale more of a tadpole-like shape, and reflects in differences in diving behavior: 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.[4][11]
Range
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,[4][7] although they very rarely cross the Antarctic Convergence.[6]
Foraging behaviour
The presence of pygmy blue whales is strongly linked to prey availability, with upwelling being a strong predictor. [12] The pygmy blue whale feeds on krill that are more ephemeral and smaller in size, compared to the diet of the Antarctic blue whale. [12] Conditions favourable for krill are created in the Perth Canyon area, which results in aggregations of euphausiid species, including krill. [13] This attracts pygmy whales while they are on their northern migration. [13] Aggregations of their preferred krill are also found along the south eastern Australia “Bonney” coast during the late autumn and summer. [12] This is where The Bonney Upwelling occurs, which results in cold, nutrient-rich waters coming up to the surface from the deep sea and submarine canyons, allowing krill to flourish. [13] Pygmy blue whales are attracted to the Bonney coast due to the abundance of krill, with three zones being utilised by them – the central, eastern, and western zone. [13] At these areas of large krill aggregations, pygmy blue whales undertake feeding lunges and pass large amounts of seawater through the bristles of their baleen plates to filter the water and capture prey. [14]
Diving behaviour
The migratory dives of pygmy blue whales minimise energy expenditure by maintaining the bottom depth to where wave drag is minimised. [15] This is just below the depth threshold of where the effect of surface drag on the whale is removed. [15] It allows the whale to save energy and maximise horizontal movement by keeping drag at a minimum and staying close to the surface for air supply. [15] This strategy places them at a higher risk of ship strike, as the range of their migratory dives overlaps with those of large container ship drafts, which is less than 24m. [15]
Along with migratory dives, they perform feeding dives, which include a lunge, and exploratory dives, which are relatively deep dives that do not include a lunge. [15]
Feeding dives: [15] Mean maximum depth: 129 ± 183 m. Mean dive duration: 7.6 min. Maximum dive duration: 17.5 min.
Migratory dives: [15] Mean bottom depth of migratory dives: 14 ± 4 m. Mean dive duration: 5.2 min. Maximum dive duration: 26.7 min.
Exploratory dives: [15] Mean maximum depth: 107 ± 81 m. Mean dive duration: 8.6 min. Maximum dive duration: 22.05 min.
Pygmy blue whales spend over 90% of their time in the top 24m of the water column, and the mean depth is less than 24m for 99% of their migratory dives. [15] Their diving behaviour also reflects the structure of their songs, with them commonly performing depth undulations that coincide with song production patterns. [14]
Acoustic behaviour
Pygmy blue whale populations can be differentiated acoustically, with each producing calls with slight differences. [16] They do not show any other morphological differences, and genetic data is limited. [16] Three of the four distinct call types attributed to blue whales in the Indian Ocean are attributed to pygmy whales. [16] These were first recorded in Madagascar, Sri Lanka, and Australia. [16] In 1984, the Sri Lanka call was first recorded, with the Madagascar call being recorded following this, in 1996. [16] The most common call type was the Sri Lanka call. [17] There are differences in the three call types regarding frequency content and modulation, as well as the number of units, which suggests how these are from three distinct ‘acoustic populations.' [12] The calls are composed of units, which are sections of the song separated by a period of silence. [16] The call of the Madagascan pygmy blue whale has two units, and the call of the Sri Lankan pygmy blue whale has three units. [16] The most complex call is of the Australian pygmy blue whale, which is considered to be three units with several variations in the order of the units. [16] The function of the calls has been related to the prevention of interbreeding between different populations. [18] It has also been related to helping with navigation, prey detection, and encouraging pair formation, as songs are detected year-round at high-latitude feeding areas. [12] The whales are more vocally active during the night compared to the day. [19] There are links to climate cycles affecting the behaviour of pygmy blue whales, with there being up to 10 times more directions of songs during La Niña compared to in neutral or El Nino years. [12]
Threats
The migratory route of pygmy blue whales goes through locations that come in contact with offshore oil and gas activities, fisheries, and shipping routes, which exposes them to the main threats of vessel collisions, entanglement in fishing gear, noise interferences, and pollution. [20][21]
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).[citation needed]
A new population of pygmy blue whales was discovered in the Indian Ocean in 2017, with the aid of nuclear bomb detectors.[22] The Chagos population was determined to be undiscovered before by their unique song.
Specimens
MNZ MM002191, collected Motutapu Island, Hauraki Gulf, New Zealand, September 1994, now in Te Papa collection.[23]
The blue whale is a marine mammal and a baleen whale. Reaching a maximum confirmed length of 29.9 m (98 ft) and weighing up to 199 t, it is the largest animal known ever to have existed. The blue whale's long and slender body can be of various shades of greyish-blue on its upper surface and somewhat lighter underneath. Four subspecies are recognized: B. m. musculus in the North Atlantic and North Pacific, B. m. intermedia in the Southern Ocean, B. m. brevicauda in the Indian Ocean and South Pacific Ocean, and B. m. indica in the Northern Indian Ocean. There is a population in the waters off Chile that may constitute a fifth subspecies.
Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and porpoises. Dolphins and porpoises may be considered whales from a formal, cladistic perspective. Whales, dolphins and porpoises belong to the order Cetartiodactyla, which consists of even-toed ungulates. Their closest non-cetacean living relatives are the hippopotamuses, from which they and other cetaceans diverged about 54 million years ago. The two parvorders of whales, baleen whales (Mysticeti) and toothed whales (Odontoceti), are thought to have had their last common ancestor around 34 million years ago. Mysticetes include four extant (living) families: Balaenopteridae, Balaenidae, Cetotheriidae, and Eschrichtiidae. Odontocetes include the Monodontidae, Physeteridae, Kogiidae, and Ziphiidae, as well as the six families of dolphins and porpoises which are not considered whales in the informal sense.
Rorquals are the largest group of baleen whales, comprising the family Balaenopteridae, which contains nine extant species in two genera. They include the largest known animal that has ever lived, the blue whale, which can reach 180 tonnes, and the fin whale, which reaches 120 tonnes ; even the smallest of the group, the northern minke whale, reaches 9 tonnes.
The fin whale, also known as the finback whale or common rorqual, is a species of baleen whale and the second-longest cetacean after the blue whale. The biggest individual reportedly measured 26 m (85 ft) in length, with a maximum recorded weight of 77 to 81 tonnes. The fin whale's body is long, slender and brownish-gray in color, with a paler underside to appear less conspicuous from below (countershading).
Baleen whales, also known as whalebone whales, are marine mammals of the parvorder Mysticeti in the infraorder Cetacea, which use keratinaceous baleen plates in their mouths to sieve planktonic creatures from the water. Mysticeti comprises the families Balaenidae, Balaenopteridae (rorquals), Eschrichtiidae and Cetotheriidae. There are currently 16 species of baleen whales. While cetaceans were historically thought to have descended from mesonychians, molecular evidence instead supports them as a clade of even-toed ungulates (Artiodactyla). Baleen whales split from toothed whales (Odontoceti) around 34 million years ago.
The minke whale, or lesser rorqual, is a species complex of baleen whale. The two species of minke whale are the common minke whale and the Antarctic minke whale. The minke whale was first described by the Danish naturalist Otto Fabricius in 1780, who assumed it must be an already known species and assigned his specimen to Balaena rostrata, a name given to the northern bottlenose whale by Otto Friedrich Müller in 1776. In 1804, Bernard Germain de Lacépède described a juvenile specimen of Balaenoptera acuto-rostrata. The name is a partial translation of Norwegian minkehval, possibly after a Norwegian whaler named Meincke, who mistook a northern minke whale for a blue whale.
The common minke whale or northern minke whale is a species of minke whale within the suborder of baleen whales.
The Antarctic minke whale or southern minke whale is a species of minke whale within the suborder of baleen whales. It is the second smallest rorqual after the common minke whale and the third smallest baleen whale. Although first scientifically described in the mid-19th century, it was not recognized as a distinct species until the 1990s. Once ignored by the whaling industry due to its small size and low oil yield, the Antarctic minke was able to avoid the fate of other baleen whales and maintained a large population into the 21st century, numbering in the hundreds of thousands. Surviving to become the most abundant baleen whale in the world, it is now one of the mainstays of the industry alongside its cosmopolitan counterpart the common minke. It is primarily restricted to the Southern Hemisphere and feeds mainly on euphausiids.
Balaenoptera is a genus of rorquals containing eight extant species. Balaenoptera comprises all but two of the extant species in its family ; the genus is currently polyphyletic, with the two aforementioned species being phylogenetically nested within it.
The sei whale is a baleen whale. It is one of ten rorqual species, and the third-largest member after the blue and fin whales. It can grow to 19.5 m (64 ft) in length and weigh as much as 28 t. Two subspecies are recognized: B. b. borealis and B. b. schlegelii. The whale's ventral surface has sporadic markings ranging from light grey to white, and its body is usually dark steel grey in colour. It is among the fastest of all cetaceans, and can reach speeds of up to 50 km/h (31 mph) over short distances.
Whale conservation refers to the conservation of whales.
Rice's whale, also known as the Gulf of Mexico whale, is a species of baleen whale endemic to the northern Gulf of Mexico. Initially identified as a subpopulation of the Bryde's whale, genetic and skeletal studies found it to be a distinct species by 2021. In outward appearance, it is virtually identical to the Bryde's whale. Its body is streamlined and sleek, with a uniformly dark charcoal gray dorsal and pale to pinkish underside. A diagnostic feature often used by field scientists to distinguish Rice's whales from whales other than the Bryde's whale is the three prominent ridges that line the top of its head. The species can be distinguished from the Bryde's whale by the shape of the nasal bones, which have wider gaps due to a unique wrapping by the frontal bones, its unique vocal repertoire, and genetic differences.
↑ "Balaenoptera musculus — Blue Whale". Canberra: Australian Government: Department of the Environment and Water Resources. 2007. Retrieved 15 June 2007.
1 2 3 4 5 6 McCauley, R. D., Gavrilov, A. N., Jolliffe, C. D., Ward, R., & Gill, P. C. (2018). Pygmy blue and Antarctic blue whale presence, distribution and population parameters in southern Australia based on passive acoustics. Deep-Sea Research. Part II, Topical Studies in Oceanography, 157–158, 154–168. https://doi.org/10.1016/j.dsr2.2018.09.006
1 2 3 4 Jolliffe, C. D., McCauley, R. D., Gavrilov, A. N., Jenner, C., & Jenner, M. N. (2021). Comparing the acoustic behaviour of the eastern Indian Ocean pygmy blue whale on two Australian feeding grounds. Acoustics Australia, 49(2), 331–344. https://doi.org/10.1007/s40857-021-00229-2
1 2 Davenport, A. M., Erbe, C., Jenner, M.-N. M., Jenner, K. C. S., Saunders, B. J., & McCauley, R. D. (2022). Pygmy blue whale diving behaviour reflects song structure. Journal of Marine Science and Engineering, 10(9), 1227-. https://doi.org/10.3390/jmse10091227
1 2 3 4 5 6 7 8 9 Owen, K., Jenner, C. S., Jenner, M. N. M., & Andrews, R. D. (2016). A week in the life of a pygmy blue whale: Migratory dive depth overlaps with large vessel drafts. Animal Biotelemetry, 4(1). https://doi.org/10.1186/s40317-016-0109-4
1 2 3 4 5 6 7 8 Leroy, E. C., Royer, J. Y., Alling, A., Maslen, B., & Rogers, T. L. (2021). Multiple pygmy blue whale acoustic populations in the Indian Ocean: whale song identifies a possible new population. Scientific Reports, 11(1), 8762–21. https://doi.org/10.1038/s41598-021-88062-5
↑ Stafford, K. M., Chapp, E., Bohnenstiel, D. R., & Tolstoy, M. (2011). Seasonal detection of three types of “pygmy” blue whale calls in the Indian Ocean. Marine Mammal Science, 27(4), 828–840. https://doi.org/10.1111/j.1748-7692.2010.00437.x
↑ Truong, G., & Rogers, T. L. (2023). La Niña conditions influence interannual call detections of pygmy blue whales in the eastern Indian Ocean. Frontiers in Marine Science, 9. https://doi.org/10.3389/fmars.2022.850162
↑ Gavrilova, A. N., & McCauley, R. D. (2013). Acoustic detection and long-term monitoring of pygmy blue whales over the continental slope in southwest Australia. The Journal of the Acoustical Society of America, 134(3), 2505–2513. https://doi.org/10.1121/1.4816576
↑ Ferreira, L. C., Jenner, C., Jenner, M., Udyawer, V., Radford, B., Davenport, A., Moller, L., Andrews-Goff, V., Double, M., & Thums, M. (2024). Predicting suitable habitats for foraging and migration in Eastern Indian Ocean pygmy blue whales from satellite tracking data. Movement Ecology, 12(1), 42–20. https://doi.org/10.1186/s40462-024-00481-x
↑ Croll, D., Tershy, B., Brownell, R. L., & de Vos, A. (2016). Anthropogenic threats and conservation needs of blue whales, Balaenoptera musculus indica, around Sri Lanka. Journal of Marine Biology, 2016(2016), 1–12. https://doi.org/10.1155/2016/8420846
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