Wikipedia talk:WikiProject Cetaceans

The first toothless ancestors of Mysticetes appeared before the first radiation in the late Oligocene.^[25] Eomysticetus and others like it showed no evidence in the skull of echolocation abilities, suggesting they mainly relied on their eyesight for navigation. 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 had baleen and been filter feeders.^[26][21]

Anatomy

Baleen whale have two flippers on the front, near the head. The hind legs are enclosed inside the body, and are thought to be

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

Like all mammals, baleen whales breathe air and must surface periodically to do so. Their nostrils, or

The eyes of baleen whales are relatively small for their size and are positioned near the end of the mouth. This is probably because they feed on slow or immobile prey, and that most sunlight does not pass 30 feet (9.1 m), and hence does not need acute vision. A whale's eye is adapted for seeing both in the photic and aphotic zones by increasing or decreasing the pupil's size to prevent damage to the eye. As opposed to land mammals, whales have spherical eyeballs. The retina is surrounding by reflective layer of cells (tapetum lucidum), which bounces back at the retina, enhancing eyesight in dark areas. However, light is bent more near the surface of the eye when in air as opposed to water; consequently, they can see much better in the air than in the water. The eyeballs are protected by a thick outer layer to prevent abrasions, and an oily fluid (instead if tears) on the surface of the eye. Baleen whales appear to have limited color vision, as they lack S-cones.^[33]

The mysticete ear is adapted for hearing underwater, where it can hear sound frequencies as low as 7

Before diving, baleen whales typically stay near the surface and take 10 to 15 breaths for around three minutes and dive for eight minutes. Their unique lungs are built to collapse under the pressure instead of resisting the pressure would damage the lungs. The whale lungs are very efficient at extracting oxygen from the air, usually 80%, whereas humans only extract 20% of oxygen from inhaled air. Lung volume is relatively low compared to terrestrial mammals due to the inability of the respiratory tract to hold gas while diving. Doing so may cause serious complications such as embolism. Unlike other mammals, the lungs of baleen whales lack lobes and are more sacculated shaped. Like in humans, the left lung is smaller than the right to make room for the heart.^[39] To conserve oxygen, blood is rerouted from pressure-tolerant-tissue to internal organs,^[40] and they have a high concentration of myoglobin which allow them to hold their breath longer.^[41]

Thermoregulation

Baleen whales conserve heat with their large and compact body size, and insulating blubber. In addition, they have a dense network of blood vessels (rete mirabile) which prevents heat-loss. In most mammals, heat is lost in their extremities, so warm blood in arteries is surrounded by veins to prevent heat loss during transport. As well as this, heat inevitably given off by the arteries warms blood in the surrounding veins as it travels back into the core. This is otherwise known as countercurrent exchange. To counteract overheating while in warmer waters, whales reroute blood to the skin to accelerate heat-loss.^[33]

Sleep

Unlike most animals, whales are conscious breathers. All mammals sleep, but whales cannot afford to become unconscious for long because they may drown. They are thought exhibit unihemispheric slow-wave sleep, in which they sleep with half of the brain while the half remains active. This behavior was only documented in toothed whales until footage of a humpback whale sleeping (vertically) was shot in 2014.^[42]

Behavior

Baleen whales, being fully aquatic, spend their lives in the water; unable to haul themselves onto shore, they must raise young, molt, rest, and thermoregulate in the water. Several species are known to migrate vast distances, to calving grounds in tropical waters, and each species has their own breeding season. The migration cycle is repeated annually.

All baleen whales are carnivorous and predatory. Different kinds of prey are found in different abundances depending on location, for example, Antarctic residents mostly feed on

Baleen whales, due to their great size, do not have any natural predators. However, calves can be preyed on by the

Before reaching adulthood, baleen whales grow at an extraordinary rate. In the

The same life pattern can be seen in other balaenopterids; they mate in warm waters in winter to give birth almost a year later.^[43] A 7– to 11-month lactation period is normally followed by a year of rest before mating starts again. Adults normally start reproducing when 5–10 years old and reach their full length after 20–30 years.^[57][58][59] 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.^[60] Unusual for a baleen whale, female minkes (and humpbacks) can become pregnant immediately after giving birth; in most species, there is a 2-to-3-year calving period. 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. Baleen whales are K-strategists, meaning they raise one calf at a time, have a long life-expectancy, and a low infant mortality rate.^[61]

Intelligence

Unlike their toothed whale counterparts, baleen whales are hard to study due to their immense size. Intelligence tests such as the

Current whaling nations are Norway, Iceland, and Japan, despite their joining to the IWC, as well as the aboriginal communities of Siberia, Alaska, and northern Canada.^[72] Subsistence hunters typically use whale products for themselves and depend on them for survival. National and international authorities have given special treatment to aboriginal hunters since their methods of hunting are seen as less destructive and wasteful. This distinction is being questioned as these aboriginal groups are using more modern weaponry and mechanized transport to hunt with, and are selling whale products in the marketplace. Some anthropologists argue that the term "subsistence" should also apply to these cash-based exchanges as long as they take place within local production and consumption. In 1946, the IWC placed a moratorium, limiting the annual whale catch.^[73]

Conservation and management issues

As of 2013, International Union for Conservation of Nature (IUCN) recognizes 15 mysticete species. One species—the North Atlantic right whale—is endangered with only around 400(±50) individuals left, and four more are also considered as Endangered" (North Pacific right whale, the blue whale, the fin whale, and the Sei whale), and another 5 ranked as Data deficient (Bryde's whale, Eden's whale, Omura's whale, Southern minke whale, and pygmy right whale).^[74] Species that live in polar habitats are vulnerable to the effects of recent and ongoing climate change, particularly declines in sea ice, as well as ocean acidification.^[75]

The whale watching industry and anti-whaling advocates argue that whaling catches "friendly" whales that are curious about boats, as these whales are the easiest to catch. This analysis claims that once the economic benefits of hotels, restaurants and other tourist amenities are considered, hunting whales is a net economic loss. This argument is particularly contentious in Iceland, as it has among the most-developed whale-watching operations in the world and the hunting of minke whales resumed in August 2003. Brazil, Argentina and South Africa argue that whale watching is a growing billion-dollar industry that provides more revenue than commercial whaling would provide.^[76] Peru, Uruguay, Australia, and New Zealand also support proposals to permanently forbid whaling South of the Equator, as Indonesia is the only country in the Southern Hemisphere with a whaling industry. Anti-whaling groups claim that developing countries which support a pro-whaling stance are damaging their economies by driving away anti-whaling tourists.^[77]

Commercial whaling was historically important for world economy. All species were exploited, and as one type's stock depleted, another type was targeted. The scale of whale harvesting decreased substantially through the 1960's as all whale stocks had been depleted, and practically stopped in the 1988 after the

Baleen whale continue to be harvested. However, only three nations take whales: Iceland (despite being a member of the IWC), Norway, and Japan. Iceland and Norway were part of the IWC, but withdrew in 1992 and 1993, respectively, and continued hunting minke whales; despite Iceland's rejoining in 2006, they still continue to catch whales. ^[82] Japan, being part of the IWC, whales under the Scientific Permit stated in Article VIII in the Convention for the Regulation of Whaling.^[83] Japan has had two main research programs: JARPA and JARPN. JARPN is focused in the North Pacific and JARPA around the Antarctic. JARPA mainly caught Antarctic minke whales, catching nearly 7,000; to a far lesser extent, they also caught fin whales.^[84] Animal-rights activist groups (such as the Greenpeace^[85]) object to Japan's scientific whaling, with some calling a substitute for commercial whaling.^[86] In 2014, the United Nations judicial branch banned the taking of whales for any purpose in the Southern Ocean Whale Sanctuary,^[87] however Japan refuses to stop whaling and has only promised to cut their annual catches by a third (around 300 whales per year).^[88]

Baleen whales can also be effected by humans in more indirect ways. For species like the North Atlantic right whale, which migrates through some of the world's busiest shipping lanes, the biggest threat is from being struck by ships. The Lloyd's mirror effect results in low frequency propeller sounds not being discernible near the surface, where most accidents occur. Combined with spreading and acoustic shadowing effects, the result is that the whale is unable to hear an approaching vessel before it has been run over or entrapped by the hydrodynamic forces of the vessel's passage.^[89] The ever-increasing amount of ocean noise, including sonar, drowns out the vocalizations produced by whales, notably in the blue whale which produces the loudest vocalization, which makes it harder for them to communicate.^[90][91] Blue whales stop producing foraging D calls once a mid-frequency sonar is activated, even though the sonar frequency range (1–8 kHz) far exceeds their sound production range (25–100 Hz).^[92] Poisoning from toxic substances such as Polychlorinated biphenyl (PCB) is generally low due to their low trophic level.^[93] Some baleen whales can become victims of bycatch, which is especially serious for North Atlantic right whales, considering there are only 450 left.^[94] Right whales feed with wide-open mouths, risking entanglement in any rope or net fixed in the water column. Rope wraps around their upper jaws, flippers and tails. Some are able to escape, but others remain tangled. If observers notice, they can be successfully disentangled, but others die over a period of months. Other whales, such as humpback whales, can also be entangled.^[95]

In captivity

Baleen whales have rarely been kept in captivity. Their large size and appetite make them expensive creatures to maintain. Pools of proper would also be very expensive to build. For example, a single gray whale calf would need to eat 475 pounds (215 kg) of fish per day, and the pool would have to accommodate the 13-foot (4.0 m).