Baleen whale

Baleen whales Temporal range: late Eocene–Recent PreꞒ Ꞓ 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, while 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"moustache" + κῆτος "whale"), which, although obviously more appropriate and occasionally used in the past, has been superseded by "Mysticeti".^[3]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

Paired blowholes of a humpback and the V-shaped blow of a right whale

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 8 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

Diet

In the Southern Hemisphere, huge concentrations of krill are found during summers, the food preferred by baleen whales. In the Northern Hemisphere, the prey available 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 filter-feeders; they consume vast numbers of small organisms by vacuum-cleaning the ocean and not, like toothed whales, by catching prey individually. To achieve this, baleen whales typically seek out a concentration of 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 (42.5-52.5 ft) long. When it reaches sexual maturity after 5–10 years, it will be 20 to 24 m (65.6–79 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 (16.5–18 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

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
    - †Micromysticetus
  - †Family Eomysticetidae
    - †Eomysticetus
    - †Tohoraata
    - †Yamatocetus
- Clade Balaenomorpha
  - Superfamily Balaenoidea
    - Family Balaenidae: right whales and bowhead whale
      - Balaena – bowhead whales
      - †Balaenella
      - †Balaenotus
      - †Balaenula
      - Eubalaena – right whales
      - †Eucetites
      - †Idiocetus
      - †Morenocetus
      - †Peripolocetus
    - Family Neobalaenidae
      - Caperea, pygmy right whale
      - †Miocaperea
  - Clade Thalassotherii
    - †Hibacetus
    - †Isocetus
    - Family Cetotheriidae
      - †Brandtocetus
      - †Cephalotropis
      - †Cetotherium
      - †Eucetotherium
      - †Herentalia
      - †Herpetocetus
      - †Joumocetus
      - †Kurdalagonus
      - †Metopocetus
      - †Mixocetus
      - †Nannocetus
      - †Otradnocetus
      - †Palaeobalaena
      - †Piscobalaena
      - †Titanocetus
      - †Vampalus
      - †Zygiocetus
  - 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 (invalid subgroup)^[26]
      - †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 incertae sedis
- Amphiptera (existence unconfirmed)
- †Horopeta^[29]
- †Imerocetus
- †Mesocetus (nomen dubium)^[28]
- †Mioceta (nomen dubium)^[26]
- †Piscocetus
- †Siphonocetus (nomen dubium)^[26]
- †Tretulias (nomen dubium)^[26]
- †Ulias (nomen dubium)^[26]

Species

There are 10 recognized species of baleen whales.^[30]

Species of Whales
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. Only 1966, when it became obvious not many blue whales were left, did the IWC declare the blue whale a protected species. Blue whale produce very low frequency sounds (even below 20 Hz), which can be detected over large distances. ^[31] Average length is 24-27 m. The largest whale found was 33.58 m long. Females are larger than males. Typical weight is 100-120 tonnes, up to 190 tonnes. The skin is blue-grey coloured, mottled with grey-white. The large body is very broad. There is a large ridge on the head leading from the tip of the snout to the blowholes. The region of the blowholes is raised. A very small dorsal fin is located about 25% of the length in front of the tail flukes. The flippers are long and thin. The tail flukes are relatively small. There are 55-88 grooves extending from the chin to the navel. These grooves allow the mouth to extend considerably during feeding. The tongue, palate and baleen are black. The baleen is wide and relatively short (less that 1 m in length). While it has a worldwide distribution, it feeds in polar waters in summer and spends the winter in tropical and subtropical waters. Blue whales usually swim alone or in groups of 2 or 3 animals. They may group together on feeding grounds and form mixed-species groups with fin whales. The blue whale feeds almost exclusively on krill, rarely on small fish, such as capelin and sardines. Abundance: probably about 11,200 worldwide. In the North Atlantic there are only a few hundred blue whales left. Although the numbers are increasing, the blue whale is still endangered.^[32]
Bowhead whale (Balaena mysticetus)	The bowhead whale has been the target of early whaling operations. It was hunted for its oil and baleen. The Unuit people occasionally take a few whales in the Bering/Chukchi/Beaufort Sea area. ^[33] Typical length is 14-18 m. Females are slightly larger than males. Average weight is 60-90,000 kg. The bowhead whale is a very stocky animal with a large head. The mouth is bowed strongly upward. The skin is smooth and remarkably free of parasites. They are blue-black in colour with random light patches on the stomach and lower jaw. There is no dorsal fin. The flippers are relatively small and paddle-shaped. The tail flukes are wide and pointed. The baleen plates are narrow (30 cm) and very long (up to 4.3 m). Its range is in the arctic waters, near the pack ice. There are 4 main bowhead whale areas: Spitzbergen, Hudson Bay/Davis Strait, Okhotsk Sea and Bering/Chukchi/Beaufort Sea. Usually the bowhead is seen alone or in small groups of up to 3 animals. It feeds on small crustaceans. The Bering/Chukchi/Beaufort Sea has about 7,800 animals. The Spitzbergen stock is probably extinct and the populations in the other areas have probably only a few hundred animals.^[32]
Bryde's whale (Balaenoptera edeni)	Bryde's whale is easily confused with the sei whale. However, at close range, Bryde's whale can be easily recognized by the 3 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. ^[34] Average length is 11.5-14.5 m and average weight is 10-20,000 kg. 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 gray on the back and lighter on the belly. They sometimes have light oval scars, caused by cookie-cutter sharks. The dorsal fin is small and very falcate (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 individuals. They feed mainly on schooling fish, such as pilchards and sardines and on crustaceans and squid.Abundance: The North Pacific population is probably about 20-30,000 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 far less than other rorqual whales. They hardly ever show their tails before diving deep. ^[35] Size is 18-22 m, up to 27 m. Females are larger than males. Northern hemisphere fin whales are on average 1½ m shorter than Southern hemisphere fin whales. Weight ranges from 30 to 75,000 kg. The fin whale is a long and slender whale. The head resembles that of the blue whale. The fin whale is dark gray to brown in colour, with flanks that lighten towards the belly. The dark colour extends farther down on the left side than on the right, which is a unique feature in cetaceans. Most animals have a light chevron just behind the head. The large dorsal fin (60 cm high) is placed far back. The flippers are thin and pointed. The tail flukes are large, thin and pointed and look a lot like blue whale flukes. It has a worldwide distribution, in deeper water. It is usually found in groups of up to 10 animals, but larger groups (up to 100) are not uncommon. Its diet is mainly small crustaceans, but Northern hemisphere fin whales also feed on fish, such as herring, capelin and mackerel. There are roughly 100,000 in the southern hemisphere, but only 30,000 in the northern hemisphere, split 2 to 1 between the North Pacific and the North Atlantic.^[32]
Gray whale (Eschrichtius robustus)	The gray whale spends the winter in San Ignacio lagoon, Baja California, Mexico. In this area, a lot of whale watching trips are organised and sometimes whales come so close to the boats that they can be touched. In summer they move to Alaska to feed. They travel along the US coast and the gray 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 m in length and weighs up to 27,000 kg. The gray whale is mottled gray all over. The skin on the back has large yellow and white coloured patches caused by parasites like barnacle and whale lice (small crustaceans). The mouth is slightly bowed. They have more bristles on the tips of their upper and lower jaws than any other whale species. The gray whale has no dorsal fin but a number of bumps on the back and tail stock. The flippers are large and paddle-shaped. The baleen plates are yellowish and about 40 cm long, with long, thick bristles. It resides in the North Pacific only. The grey whale used to be present in the North Atlantic as well, but has been hunted to extinction there. In summer, they feed in the Bering Sea. During migration, females with calves swim together in groups of about 6 adults. Later in the migration, there are groups of 3-5 non-pregnant females with 1 or 2 males. The last on the migration are juvenile animals. The gray whale feeds on the bottom. The prey consists of crustaceans, molluscs and small fishes. The Eastern population is probably about 21,000 animals and is increasing in size at a rate of about 3.2% per year. The Western Pacific population is small, probably 100-200 animals. The gray whale is no longer considered endangered.^[32]
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 reproduction. 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, whale spend the winter near Hawaii or Baja Californian and in summer move to Alaska to feed.^[36] This species is up to 19 m long and weighs up to 48,000 kg. 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 3 isolated populations: North Pacific, North Atlantic and Southern Hemisphere. On the calving grounds, they usually form groups of about 10-12 animals. During migration they travel in groups of 3-4. It feeds on krill, plankton, sardines, capelin and other small schooling fish. 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]
Minke whale (Balaenoptera acutorostrata)	The minke whale has become 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. Recently, commercial fisheries for minke whales has started again in Norway. In 1996, the Norwegian whalers took 116 minke whales and in 1997 503 whales. In Greenland, the aboriginal people are allowed to take 465 minke whales in 2 years. ^[37] This whale species is 7 to 10 m. It weighs 4,500 to 9,000 kg. 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 falcate dorsal fin, which looks like the dorsal fin of the bottlenose dolphin. Most Pacific animals have a light chevron on their flanks. It prefers temperate waters, around the world. They are usually found in small groups of 6 animals or less. They feed mainly on shoaling fish, such as herring, cod and capelin, but also on krill and plankton. In the North Pacific there are 18,000-27,000 animals, in the Northeastern Atlantic: 90-135,000 animals, in the Central Atlantic about 60,000 animals and in the Southern Hemisphere: 200-400.000 animals.^[32]
Pygmy right whale (Caperea marginata)	The pygmy right whale is the smallest baleen whale species. Its common name suggests it is closely related to the right whales, but that is not the case. The name comes from its appearance, mainly the shape of the mouth. Very little is known about this species. Since it is small and usually swims alone it is very difficult to find in the open sea. Most data is derived from dead stranded animals. ^[38] It's length is 5.5-6.5 m. It weighs 3,000-4,000 kg. The lower jaw is bowed and protrudes slightly. The body is stocky. They have a dark-coloured back, which becomes darker with age and a pale belly. This whale has a prominent dorsal fin. The flippers are small and rounded and located under the body. The tail flukes are broad. The baleen plates are yellowish and are up to 70 cm in length. It is only known from the Southern hemisphere and usually is solitary. Diet is not well known, but probably plankton.^[32]
Right whale (Eubalaena glacialis (Northern), Eubalaena australis (Southern)	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 rorqual whales start. ^[39] This 11-18 m long species weighs 30-75,000 kg. The right whale is extremely fat. There are numerous callosities on the mouth and head, caused by whale lice (small crustaceans). They are black with large white patches on the belly. They have no dorsal fin and their flippers are paddle-shaped. The tail flukes are very wide, thin and pointed. Its distribution is in temperate oceans worldwide. The Southern right whale can be found from the Antarctic to Australia and South America and into the Indian Ocean. The Northern right whale is found in the North Pacific, from Japan and Baja California to the Aleutians. In the North Atlantic, the Northern right whale occurs from Florida and Spain in the South to Bear Island and Spitzbergen in the north. Its social structure is usually small groups of up to 5 animals. It feeds mainly on krill. In the Northwest Atlantic about 1,000 animals are left, the Northeast Atlantic population is believed to be near extinction. Also, the North Pacific population is probably nearly extinct. There are no signs of recovery in the Northern right whale populations. The total population of Southern right whales is probably about 1,500 animals and may be recovering slightly.^[32]
Sei whale (Balaenoptera borealis)	The sei whale is probably the fastest swimmer among the baleen whales. It can reach speeds of close t 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 quota were set for these species until 1964. The catches were also recorded together. Consequently we have no accurate catch statistics from before that date. In the 60s, the annual catch of sei whales was 10-15,000 animals/year. The hunt on sei whales was stopped in the 70s. ^[40] Typical males are 12-18 m long, while females are up to 20 m long. Males weigh up to 22,000 kg, females up to 24,000 kg. The sei whale is dark gray 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 cookie-cutter 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 called sei; The association with this fish gave the whale its name), anchovies, herring, cod and sardines. 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 animals, the North Pacific population about 13,000 and the Antarctic populations about 40,000. This species is still vulnerable.^[32]