Baleen whale

Baleen whales Temporal range: late Eocene–Recent PreЄ Є O S D C P T J K Pg N
Humpback whale breaching
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Clade:	Cetancodontamorpha
Suborder:	Whippomorpha
Infraorder:	Cetacea
Parvorder:	Mysticeti Cope 1891
Families
see text

The baleen whales (Mysticeti), also called whalebone whales, comprise one of two parvorders of the artiodactyl infraorder Cetacea (whales, dolphins, and porpoises).^[1] They are the edentulous whales, characterized by having baleen plates for filtering food from water, rather than teeth like in the toothed whales (Odontoceti). Living species of Mysticeti have teeth only during the embryonic phase, whereas fossil Mysticeti had teeth before baleen evolved.

Etymology

The taxonomic name "Mysticeti" (Latin, plural) apparently derives from a translation error in early copies of Aristotle's Historia Animalium, in which "ὁ μῦς τὸ κῆτος" (ho mus to kētos, "the mouse, the whale so called") was mistakenly run together as "ὁ μυστικῆτος" (ο mustikētos, "the Mysticetus"),^[2] which Rice 1998 assumed was an ironic reference to the animals' great size.^[3] An alternate name for the suborder is "Mystacoceti" (from Greek μύσταξ "moustache" + κῆτος "whale"), which, although obviously more appropriate and occasionally used in the past, has been superseded by "Mysticeti".^[3]

Anatomy

Baleen whales vary considerably in size

Baleen whales are generally larger than toothed whales, and females are bigger than males. This group includes the largest known animal species, the blue whale.

The members of the four recognized families of baleen whales can be distinguished by several external and internal features:^[3]

• The right whales (Balaenidae, the "black" right whales and the bowhead whale) are robust, have an arched upper jaw, and long and narrow baleen plates. Their heads are remarkably large — one-third of the body length — and are equipped with a long, thin rostrum and huge bowed lower lips, but lack ventral grooves. The coronoid process is missing in the lower jaw and the cervical vertebrae are fused.
• The rorquals (Balaenopteridae) have short heads — less than a quarter of the body length — with short and wide baleen plates. They have a mostly small dorsal fin and numerous ventral grooves. The upper jaw is long and unarched and a coronoid process is present in the lower jaw, which is bowed outwards. The cervical vertebrae are unfused.

The two remaining families are intermediate in appearance between right whales and balaenopterids:

• The pygmy right whale (Neobalenidae) have short heads — a quarter of the body length — with arched upper jaw and bowed lower lips. Their relatively long baleen plates are yellowish white with a dark outer border. Many of the ribs are broadened and flattened.
• The gray whales (Eschrichtiidae, of which only Eschrichtus robustus is extant) are robust, have short and narrow heads, with a slightly arched rostrum, and relatively small baleen plates. Ventrally, the head has two to five deep creases.

Jaw

In baleen whales, enlarged oral cavities adapted for suction feeding evolved before specializations for bulk filter feeding. In the early Eocene basilosaurid Saghacetus, the mandibular symphysis is long and rigid, the rostrum is narrow, and the edges of the maxillae are thickened, indicating an adaptation for raptorial feeding. In the toothed Oligocene mammalodontid Janjucetus, the symphysis is short and the oral cavity enlarged, the rostrum is wide, and the edges of the maxillae are thin, indicating an adaptation for suction feeding. The aetiocetid Chonecetus still had teeth, but the presence of a groove on the interior side of each mandible indicates the symphysis was elastic, which would have enabled rotation of each mandible, an initial adaptation for bulk feeding like in modern mysticetes.^[4]

Blowholes

Baleen whales have two blowholes, causing a V-shaped blow. These paired blowholes are longitudinal slits that converge anteriorly and widen posteriorly. They are surrounded by a fleshy ridge that keeps water away while the whale breathes. The septum that separates the blowholes has two plugs attached to it, making the blowholes water-tight while the whale dives.^[5]

Dentition

Mysticeti possess an incredibly unique form of dentition, known as "baleen plates" or simply "baleen". The evolution of this novel adaptation has had much study surrounding it, from its gradual appearance in ancestors, to other adaptations which relaxed evolutionary constraints on the baleen itself, and finally the genetic basis for the appearance of baleen. The evolutionary processes involved with this adaptation operated very slowly. These processes most likely include a mutation which caused the trait to arise, natural selection which then enforced the prevalence of the new trait and finally fixation of the trait within baleen populations. This is evidenced by the fossil record which shows ancestral forms of mysticeti who possess both baleen and regular teeth. Traits which unfortunately cannot be supported by the fossil record include behavioral traits. Researchers suggest that filter feeding as a behavior arose prior to the evolution of modern baleen.^[6] Instead, individuals who invested in this behavior possessed a primitive form of baleen along with common teeth. Due to the success of filter feeding as a mode of prey acquisition, it is assumed that the selectional pressures on common teeth were lessened and thus baleen was positively selected for because it increased the fitness of individuals possessing it. Having baleen also allowed for the size of these whales to increase, as they were able to occupy a new niche and expand their food source. Another aspect of studying dental evolution in baleen whales is the genetic mutation which arose to create this novel trait. Enamelysin is coded for in baleen whales in the gene known as MMP20. When studying this gene within several species of mysticete, researchers found a very interesting SINE insertion shared by eight mysticete species, which are representative of all extant mysticete species. This insertion is what caused an end to enamel production in the common ancestor of mysticeti. Researchers argue that this is evidence that there was selection against the deleterious effects typical of a SINE insertion. It is clear that this mutation in the genome, which brought out new diversity within extant mysticeti species, is the true beginning of the evolution of baleen.^[7]

Behaviour

These whales are either solitary or live in small groups called pods.

The humpback whale is particularly known for its acrobatics, but other baleen whales also break through the water surface with their bodies or beat it loudly with their fins. Some believe the male baleen whales try to show off in the presence of females to increase their mating success. Scientists speculate baleen whales and other cetaceans may engage in breaching to dislodge parasites, or scratch irritated skin. Breaching, and other behaviors like lobtailing, are also used to stun or kill nearby fish or krill.

Diet

In the Southern Hemisphere, huge concentrations of krill, the food preferred by baleen whales, are found during the summer. In the Northern Hemisphere, the available food is more variable, and, for example, humpbacks and fin whales can feed exclusively on krill around Antarctica, but prey on schooling fish in the Arctic. All baleen whales except the gray whale feed near the water surface, rarely diving deeper than 100 m (330 ft) or for extended periods. The gray whale feeds on bottom-living organisms such as amphipods in shallow waters.^[8]

Sound

Baleen whales are not known to echolocate, but bowheads swimming under ice fields probably use sound for navigation. All baleen whales, however, use sound for communication and are known to "sing", especially during the breeding season. Blue whales produce the loudest sustained sounds of any animals: their low-frequency (about 20 Hz) moans can last for half a minute, reach almost 190 decibels, and be heard hundreds of kilometres away. Adult male humpbacks produce the longest and most complex songs; sequences of moans, groans, roars, sighs, and chirps sometimes lasting more than ten minutes are repeated for hours. Typically, all humpback males in a population sing the same song over a breeding season, but the songs change slightly between seasons, and males in one population have been observed adapting the song from males of a neighbouring population over a few breeding seasons.^[9]

Filter feeding

Humpback baleen plate, with the fine hairs on interior side (facing down) of each plate

Baleen whales are carnivorous zooplankton, swim through it, either open-mouthed or gulping, and filter the prey from the water using their baleen. The baleen is a row of a large number of keratin plates attached to the upper jaw. These plates have a composition similar to those in human hair or fingernails. They are triangular in section with the larger inward-facing side bearing fine hairs that form a filtering mat.^[8]

When filter feeding, baleen whales can dynamically expand their oral cavity to accommodate enormous volumes of sea water. This is made possible by its kinetic skull joints, especially the elastic mandibular symphysis (central lower joint), which permits both dentaries to be rotated independently in two planes. This flexible jaw, which made the titanic body sizes of baleen whales possible, is not present in early whales and probably evolved within Mysticeti.^[10]

Baleen whales are either continuous or intermittent filter feeders:^[11]

Left: Baleen of a right whale showing the frontal subrostral gap
Right: Blue whale skeleton mounted with lower jaw widely open

Humpback skeleton with the "slingshot" jaw open

Balaenids, the bowhead and right whale, continuously filter water through their mouths and have several anatomical adaptations for skim feeding: a frontal cleft between the two rows of baleen plates (known as the subrostral gap) and a large depression inside the lower lip. These adaptations are unique to these mysticetes, as are the fused cervical vertebrae, the firm tongue, and the semicircular lips that can reach up to the narrow rostrum. Balaenids regularly clean their baleen of accumulated prey.^[11] Right whales are slow swimmers with large heads and mouths. Their baleen plates are narrow and very long — up to 4 m (13 ft) in bowheads — and accommodated inside the enlarged lower lip, which fits onto the bowed upper jaw. As the right whale swims, water and prey are guided in through the subrostral gap, while the baleen filters out the water.^[8] Balaenids feed chiefly on tiny copepods that are about 1 mm (0.039 in), and their baleen is finely fringed for this purpose.^[12]

Intermittently filter-feeding mysticetes include the gray whale and rorquals such as the blue whale, fin whale, and humpback. They engulf a mouthful of water from which they filter the small prey using their baleen. Rorquals have several anatomical adaptations for this lunge feeding, including a loose mandibular joint, a large throat pouch with ventral folds, and a soft and agile tongue.^[11] Rorquals are fast swimmers with small heads and have short and broad baleen plates. To catch prey, they widely open their large lower jaw — almost 90° — swim into a swarm, gulping water and prey. They expand the capacity of their mouth by expanding the ventral grooves by pressing the tongue down.^[8] Humpbacks and other balaenopterids feed on larger prey (5–20 mm (0.20–0.79 in)) and consequently have coarser fringes than have balaenids.^[12]

Life history

Female right whale with calf

Before reaching adulthood, baleen whales grow at an extraordinary rate. In the blue whale, the largest species, the fetus grows by some 100 kg (220 lb)/day just before delivery, and by 80 kg (180 lb)/day during suckling. Before weaning, the calf increases its body weight by 17 t (17 long tons; 19 short tons) and grows from 7–8 m (23–26 ft) at birth to 13–16 m (43–52 ft) long. When it reaches sexual maturity after 5–10 years, it will be 20 to 24 m (66 to 79 ft) long and possibly live as long as 80–90 years.^[13]

The same life pattern can be seen in other balaenopterids; they mate in warm waters in winter to give birth almost a year later.^[14] A 7– to 11-month lactation period is normally followed by a year of rest before mating starts again.^[14] Adults normally start reproducing when 5–10 years old^[14] and reach their full length after 20–30 years.^[15][16][17] In the smallest balaenopterid, the minke whale, 3 m (9.8 ft) calves are born after a 10-month pregnancy and weaning lasts until it has reached about 5–5.5 m (16–18 ft) after 6–7 months.^[18] Unusual for a baleen whale, female minkes (and humpbacks) can become pregnant immediately after giving birth; in most species, a 2– to 3-year calving period is the norm. In right whales, the calving interval is usually 3 years. Bowheads grow very rapidly during their first year, after which they hardly increase in size for several years. They reach sexual maturity when 13–14 m (43–46 ft) long. Some 19th-century harpoons found in harvested bowheads indicate this species can live more than 100 years.

Importance to humans

From the 11th to the late 20th centuries, baleen whales were hunted commercially for their oil and baleen. Their oil was used for cooking and making products such as margarine and lamp oils, while their baleen was used to stiffen corsets, as parasol ribs, and for the manufacture of various implements today more commonly made of plastic, such as combs and paper-creasing tools.

Evolutionary history

Skull of Llanocetus

The evolution of Mysticeti as evidenced by the fossil record, was a gradual one that involved the transition from toothed, to teeth along with baleen, and finally to strictly baleen.^[19]Llanocetus, known from the late Eocene of Seymour Island, West Antarctica, is the earliest mysticete. It is a large animal with a basilosaurid-like skull with several mysticete-like features, including a wide, flat, and dorsoventrally flattened rostrum. Its jaw had heterodont teeth separated by wide diastemata, the cheek teeth are two-rooted and palmate with accessory denticles. Additionally, fine grooves around the alveoli indicate that the palate had a rich blood supply. Llanocetus has been interpreted as a filter feeder. Other early toothed mysticeti or "archaeomysticetes" from the Oligocene are the Mammalodontidae (Mammalodon and Janjucetus) from Australia. They are small with shortened rostra, and a primitive dental formula (3.1.4.33.1.4.3).^[20]

The most derived group of toothed mysticetes is the aetiocetids: Aetiocetus, Ashorocetus, Morawanocetus, Chonecetus, and Willungacetus. They are known from the late Oligocene of the North Pacific, except Willungacetus, which is known from the early Oligocene of Australia. Specimens in which the teeth are preserved, are polydont to some degree and have 11 cheek teeth, one more than in basilosaurids. In Aeotiocetus, palatal foramina and sulci suggest their blood vessels supplied some kind of "protobaleen", although the earliest preserved baleen is from the Miocene.^[20]

In the early 1990s, the species Janjucetus hunderi was discovered in Victoria by a surfer, and was described by Fitzgerald 2006.^[21] Janjucetus was a baleen whale with sharp teeth that hunted fish and squid, as well as larger prey, potentially including sharks and dolphin-like cetaceans. These fossils hint the early baleen whales were predatory and eventually evolved into the gentler, toothless whales known today. Deméré et al. 2008 identified palatal foramina and bony impressions of the blood vessels that "feed" the baleen racks in the toothed mysticete Aetiocetus weltoni.^[22] Deméré et al. concluded this discovery implies baleen whale previously possessed both teeth and baleen, and Aetiocetus serves as an intermediate adaptive role between primitive, toothed mysticetes and more derived, toothless mysticetes.^[23]

The first baleen-bearing, toothless baleen whales (such as Eomysticetus and Micromysticetus) appeared in the late Oligocene.^[24] The Eomysticetidae had long, flat rostra that lacked teeth and had external nares located halfway up the dorsal side of the snout. Though the palate is not well-preserved in these specimens, they are thought to have been baleen filter feeders.^[20] Early baleen whales probably could not echolocate; no anatomical evidence preserved in the skulls and ear regions of any fossil baleen whales show any of the adaptations associated with echolocation as in toothed whales.^[21]

Taxonomic classification

The taxonomic classification of baleen whales was considerably re-evaluated by Bisconti, Lambert & Bosselaers 2013. They introduced a new superfamily, Thalassotherii, to avoid paraphyly within Mysticeti.^[25]

The "†" signs denote extinct families and genera.

Parvorder Mysticeti: baleen whales

• Family †Aetiocetidae^[26]
  • †Aetiocetus
  • †Ashorocetus
  • †Chonecetus
  • †Morawanocetus
  • †Willungacetus
• †Family Llanocetidae
  • †Llanocetus
• †Family Mammalodontidae
  • †Janjucetus
  • †Mammalodon
• Clade Chaeomysticeti
  • Superfamily Eomysticetoidea
    • †Family Cetotheriopsidae
      • †Cetotheriopsis
    • †Family Eomysticetidae
      • †Eomysticetus
      • †Micromysticetus
      • †Tohoraata
      • †Tokarahia
      • †Waharoa
      • †Yamatocetus
  • Clade Balaenomorpha
    • Superfamily Balaenoidea
      • Family Balaenidae: right whales and bowhead whale
        • Balaena – bowhead whales
        • †Balaenella
        • †Balaenotus
        • †Balaenula
        • Eubalaena – right whales
        • †Idiocetus
        • †Morenocetus
        • †Peripolocetus
    • Clade Thalassotherii
      • †Hibacetus
      • †Isocetus
      • Family Cetotheriidae
        • †Brandtocetus
        • †Cephalotropis
        • †Cetotherium
        • †Eucetotherium
        • †Herentalia
        • †Herpetocetus
        • †Joumocetus
        • †Kurdalagonus
        • †Metopocetus
        • †Nannocetus
        • †Otradnocetus
        • †Palaeobalaena?
        • †Piscobalaena
        • †Titanocetus?
        • †Vampalus
        • †Zygiocetus
      • Subfamily Neobalaeninae
        • Caperea, pygmy right whale
        • †Miocaperea
    • Superfamily Balaenopteroidea
      • †Eobalaenoptera
      • †Mauicetus
      • †Tiphyocetus
      • Family †Aglaocetidae
        • † Aglaocetus
        • † Isanacetus
        • † Pinocetus
      • Family Balaenopteridae: rorquals^[27]
        

        Rorqual skeleton with unfused mandibular symphysis clearly visible
        • †Archaebalaenoptera
        • Balaenoptera
        • †Burtinopsis (nomen dubium)^[28]
        • †Cetotheriophanes
        • †Diunatans
        • Megaptera – humpback whale
        • †Notiocetus
        • †Parabalaenoptera
        • †Plesiobalaenoptera
        • †Plesiocetus
        • †Praemegaptera
        • †Protororqualus
      • †Family Diorocetidae
        • †Amphicetus
        • †Diorocetus
        • †Plesiocetopsis
        • †Thinocetus
        • †Uranocetus
      • Family Eschrichtiidae
        • †Archaeschrichtius
        • †Eschrichtioides
        • Eschrichtius – gray whales
          

          Gray whale skeleton
        • †Gricetoides
        • †Megapteropsis (nomen dubium)^[26]
      • †Family Pelocetidae (invalid subgroup)^[26]
        • †Cophocetus
        • †Halicetus
        • †Parietobalaena
        • †Pelocetus
      • †Family Tranatocetidae
        • †Mesocetus
        • †Mixocetus
        • †Tranatocetus
• Family incertae sedis
  • Amphiptera (existence unconfirmed)
  • †Horopeta^[29]
  • †Imerocetus
  • †Mioceta (nomen dubium)^[26]
  • †Piscocetus
  • †Siphonocetus (nomen dubium)^[26]
  • †Tretulias (nomen dubium)^[26]
  • †Ulias (nomen dubium)^[26]

Species

There are 14 recognized species of baleen whales that are still around today: Antarctic minke whale, the blue whale, bowhead whale, Bryde's whale, common minke whale, fin whale, gray whale, humpback whale, northern right whale, Omura's whale, pygmy right whale, sei whale, and southern right whale.^[30]

Species	Description	Image
Blue whale (Balaenoptera musculus)	The blue whale is the largest animal that ever lived on Earth, much larger than the largest dinosaur. This whale has been extensively hunted in the past. Between 1930 and 1971, about 280,000 blue whales have been killed. In 1966, when it became obvious not many blue whales were left, the [33]
Bowhead whale (Balaena mysticetus)	The bowhead whale was a target of early whaling operations. It was hunted for its oil and baleen. The [33]
Bryde's whale (Balaenoptera edeni)	Bryde's whale is easily confused with the sei whale. At close range, Bryde's whale can be easily recognised by the three parallel ridges on the head. The sei whale has only one central ridge. Bryde's whale is known to breach often in some areas. Bryde's whale is the least hunted of the rorqual species, mainly because it inhabits tropical and subtropical waters that were closed to whaling operations, because other species had been depleted in the area.[36] Average length is 11.5 to 14.5 metres (38 to 48 ft) and average weight is 10 to 20 metric tons (11 to 22 short tons). Females can live up to 52 years of age and males up to 55 years of age. Bryde's whale has 3 ridges on the head leading from the tip of the upper jaw to the blowholes. The Bryde's whale is dark grey on the back and lighter on the belly. They sometimes have light oval scars, caused by cookiecutter sharks. The dorsal fin is small and very curved. The flippers are medium-sized and thin, and somewhat rounded at the tip. The tail flukes are almost identical to those of the blue whale. It inhabits tropical and subtropical waters, between 40N and 40S latitude.It is usually alone or in groups of up to 10. They feed mainly on schooling fish, crustaceans and squid. Bryde's whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to take in huge amounts of water and sift through the krill and plankton within it. The North Pacific population is probably about 20,000-30,000 animals. Not much is known about other areas.[32]
Fin whale (Balaenoptera physalus)	The fin whale is a fast swimmer, reaching speeds of 30 km/hr. It occasionally jumps clear of the water but does so less than other [33]
Gray whale (Eschrichtius robustus)	The gray whale spends the winter in the lagoons of Baja California, Mexico. In summer they move to Alaska to feed. They travel along the US coast and the grey whale migration can be seen from several land-based spots along the coast. The gray whale is one of the few species who have come back from the brink of extinction. After a period of intense whaling, the species was nearly extinct, but it has recovered to the point that the US has taken it off its endangered species list. This species is 13.5 to 15 metres (44 to 49 ft) in length and weighs up to 27 metric tons (30 short tons). Average age is 50 to 70 years. The grey whale is mottled grey all over. The skin on the back has large yellow and white coloured patches caused by parasites like barnacle and [33]
Humpback whale (Megaptera novaeangliae)	The humpback whale is probably one of the best known baleen whale species. The humpback whale is famous for its songs, of which even records have been made. The function of the songs is not clear. Most likely, the songs play a role in territorial behaviour and in courting. Only the males sing. These songs can be heard over large distances. Humpback whales have developed a unique way of catching fish: they dive down, then slowly circle to the surface, blowing bubbles on the way up. This will encircle the fish in a net of bubbles. The whales then surface with open mouths in the middle of the circle, gulping up the concentrated fish. Humpback whales migrate over large distances. In the North Pacific, Humpbacks spend the winter near Hawaii or Baja Californian and in summer, move to Alaska to feed.[39] This species is up to 19 metres (62 ft) long and weighs up to 48 metric tons (53 short tons). Average age is 40 to 100 years. The humpback whale is black all over, with very long flippers, which vary in colour from black to white. There are also lighter patches on the belly and chest. The underside of the tail flukes also have patterns, which are unique for each individual. From the blowhole to the tip of the snout and laterally towards the edges of the mouth there are conspicuous hair follicles on large bumps. The dorsal fin is small and set far back (about 2/3 of the body length). Its distribution is worldwide, but they follow fixed migration patterns. In the summer, they feed in the polar regions and they migrate to warmer waters in the winter for breeding. There are three isolated populations: North Pacific, North Atlantic and Southern Hemisphere. On the calving grounds, they usually form groups of about 10-12. During migration they travel in groups of three to four. They feed on krill, plankton, and small schooling fish. Humpback whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to take in huge amounts of water and sift through the krill and plankton within it. There are about 5,500 in the North Atlantic, 2,500 in the North Pacific and about 12,000 in the Southern Hemisphere. There may also be a resident population of about 500 animals in the Indian Ocean. The humpback whale is considered to be a vulnerable species.[32][33]
Minke whale (Balaenoptera acutorostrata, Balaenoptera bonaerensis)	The minke whale became the target of whaling operations when the larger whales had declined to a level that made hunting them commercially unattractive. With all the larger whales reduced in numbers, the minke whales could multiply. Commercial fisheries for minke whales has restarted in Norway. In 1996, Norwegian whalers took 116 minke whales and in 1997, 503. In Greenland, the indigenous people are allowed to take 465 minke whales in 2 years.[40] This whale species is 7 to 10 metres (23 to 33 ft), making it the smallest of the baleen whales. Average age is 30 to 50 years. They weigh 4.5 to 9 metric tons (5.0 to 9.9 short tons). The snout is pointed, and there is a clear under-bite. The back is black, whereas the belly region is white. They have a distinctive white band on the long, thin flippers. They have a well-developed curved dorsal fin, which looks like the dorsal fin of the [33][41]
Omura's whale (Balaenoptera omurai)	Omura's whale, sometimes referred to as the dwarf fin whale, is a very mysterious type of whale. Prior to 2003, omura's whale was thought to be a dwarf variation of bryde's whale, and as a result, very little is known about them. This species was originally identified by only ten or so individuals. Their colouration has been reported in some individuals to resemble the fin whale, hence its nickname. Males reach a length of a mere 8.2 to 10.1 metres (27 to 33 ft), and females reach 9.8 to 11.5 metres (32 to 38 ft), making Omura's whale one of the smallest baleen whales. Their average weight remains unknown, as well as their average age.[42] Based on sightings, they are thought to travel alone and, rarely, in pairs. Since they are rorquals, they are believed to feed predominately on schooling fish. Omura's whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to take in huge amounts of water and sift through the krill and plankton within it. Their distribution remains unknown, but they are known to occupy the coasts of Japan, the Philippines, Indonesia, and are thought to live in the subtropical waters of the Indian ocean and the western Pacific ocean. Since this whale was discovered so recently, and their discovery was based upon nine individuals, the IUCN has listed them as "data deficient", meaning there are no accurate approximations for their population.[43]
Pygmy right whale (Caperea marginata)	The pygmy right whale is a very elusive species; they are rarely seen in the ocean and much of what is known about them comes from dead individuals that stranded themselves onto shore, and, as a result, little is known about them. This whale was once thought to be the last surviving member of the Neobalaenidae family, but its skull shape suggests that it is part of a very ancient family of whales called [33][46]
Right whale (Eubalaena glacialis, Eubalaena australis, Eubalaena japonica	These whales were named right whales, because for the early whalers they were the right ones to catch. They are slow, have lots of fat and stay afloat when killed. Only when the right and bowhead whales were depleted and factory ships were developed did the hunt for the [33]
Sei whale (Balaenoptera borealis)	The sei whale is probably the fastest swimmer among the baleen whales. It can reach speeds of close to 38 km/hr. The sei whale has been hunted extensively in the past. Because this whale resembles the Bryde's whale (only at close range can one see the single ridge on the head, whereas the Bryde's whale has 3 parallel ridges), combined quotas were set for these species until 1964. The catches were also recorded together. Consequently, there is no accurate catch statistics from before that date. In the 1960s, the annual catch of Sei whales was 10-15,000 per year. Hunting of sei whales was stopped in the 1970s.[48] Typical males are 12 to 18 metres (39 to 59 ft) long, while females are up to 20 metres (66 ft) long. Males weigh up to 22 metric tons (24 short tons), females up to 24 metric tons (26 short tons). Their average age is 50 to 70 years. The sei whale is dark grey on the back and also on the underside of the tail stock. The chin, throat and belly are white. This whale often has oval white marks, caused by lampreys and cookiecutter sharks. One long ridge runs from the tip of the upper jaw to the blowholes. The dorsal fin is large and placed far back (farther than that of the fin whale). It has a worldwide distribution, but not near the pack ice. It is usually seen alone or in pairs. When plenty of food is available they may form larger groups. Diet consists mostly of krill and other crustaceans. The sei whale also feeds on capelin, pollack (in Norwegian, they are called sei; the association with this fish gave the whale its name), anchovies, herring, cod and sardines. Sei whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to take in huge amounts of water and sift through the krill and plankton within it. This species has been depleted by over-exploitation. After the end of commercial whaling for this species in 1980, no population estimates have been made. The North Atlantic population probably consists of a few thousand, the North Pacific population about 13,000 and the Antarctic populations about 40,000. This species is still vulnerable.[32]

References

Further reading

• Bannister, John L. (2008). "Baleen Whales (Mysticetes)". In Perrin, William F.; Würsig, Bernd; Thewissen, J. G. M. Encyclopedia of Marine Mammals. Academic Press. pp. 80–89.  
• Bisconti, M.; Lambert, O.; Bosselaers, M. (2013). "Taxonomic revision of Isocetus depauwi (Mammalia, Cetacea, Mysticeti) and the phylogenetic relationships of archaic 'cetothere' mysticetes". Palaeontology 56 (1): 95–127.  
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