Whale

Whales are a large and varied group of aquatic placental marine mammals. In everyday speech, the name "whale" refers to the big members of the Cetacea group. This group includes all whale-like animals except dolphins and porpoises. Scientists can also count dolphins and porpoises as whales. All of these animals belong to the order Cetartiodactyla. Their closest living relatives on land are the hippopotamuses. There are two main kinds of whales: baleen whales and toothed whales. Baleen whales include the rorquals, right whales, the pygmy right whale, and the grey whale. Toothed whales include belugas and narwhals, the sperm whale, and the beaked whales.

Whales spend their whole lives in water. They eat, find mates, give birth, and raise their young at sea. Whales come in many sizes. The dwarf sperm whale is about 2.6 metres (8.5 ft) long. The blue whale is 29.9 metres (98 ft) long and is the largest animal known to have ever lived. The sperm whale is the largest toothed predator on Earth. In several whale species, the females are larger than the males.

Baleen whales have no teeth. Instead, they have plates of baleen, which are fringe-like structures. These plates let them push out the large mouthfuls of water they take in, while keeping the krill and plankton they eat. Toothed whales have cone-shaped teeth for catching fish or squid. Many toothed whales have such good hearing that some can still find their way even if they cannot see. Whales must come up to the surface to breathe air, though some can stay underwater for a long time. The sperm whale, for example, can stay underwater for up to 90 minutes. Whales breathe through blowholes on top of their heads. Whales are warm-blooded and have a layer of fat called blubber under their skin.

Many whales live in oceans all over the world, but most prefer the colder waters of the Northern and Southern Hemispheres. They often travel to the equator to give birth. Some whales, such as humpbacks and blue whales, can travel thousands of miles without eating. Whales make many sounds. The long songs of the humpback whale are especially well known. Whales were once hunted heavily for their products, but they are now protected by international law. The North Atlantic right whales nearly disappeared in the twentieth century. The North Pacific grey whale population is listed as Critically Endangered by the IUCN. Whales have also been part of human culture for a long time. They appear in books and films, such as the great white whale in Herman Melville's novel Moby-Dick. Today, whale watching is a popular kind of tourism around the world.

Etymology and definitions

The word "whale" comes from Old English hwæl. That word came from Proto-Germanic *hwalaz, and before that from Proto-Indo-European *(s)kʷálos. It probably meant either "large sea fish" or "sheatfish". The word is not related to the country of Wales. Sometimes "whale" is also used to include dolphins and porpoises. In this sense, it is a synonym for Cetacea.

Six kinds of ocean dolphins (Delphinidae) have "whale" in their name. Together, they are called blackfish. They include the orca, also called the killer whale, and the melon-headed whale. They also include the pygmy killer whale, the false killer whale, and two kinds of pilot whales. The term "Great Whales" refers to the species that the International Whaling Commission currently regulates. These include sperm whales, right and bowhead whales, grey whales, and some other large whales. Those other large whales are minke, Bryde's, sei, blue, and fin whales. Eden's and Omura's whales are not included.

Taxonomy and evolution

See also: List of cetaceans and List of extinct cetaceans

Whales are part of the mostly land-living mammal group Laurasiatheria. Their closest group is Cetacea. If dolphins and porpoises are left out, whales are paraphyletic. If dolphins and porpoises are counted as whales, then the sensu lato group is a clade, the Cetacea. The phylogenetic tree shows how whales and other mammals are related. Cetaceans are divided into two groups. The larger group, Mysticeti (baleen whales), has baleen. Baleen is a sieve-like structure in the upper jaw made of keratin. Baleen whales use it to filter plankton and other food from the water. Odontocetes (toothed whales) have sharp teeth instead, which they use for hunting.

Main article: Evolution of cetaceans

Whales came from land-living mammals of the artiodactyl order, which are even-toed hoofed animals. They are related to Indohyus, an extinct hoofed animal that looked somewhat like a chevrotain. Whales split from this group about 48 million years ago. Early whales, called archaeocetes, first went into the sea about 49 million years ago. They became fully aquatic 5 to 10 million years later. Over time, their bodies adapted to life in the sea, which is a marine environment. They developed hearing that carried vibrations from the jaw to the ear bone (Ambulocetus, 49 million years ago). They also developed a streamlined body and tail flukes (Protocetus, 43 million years ago). Their nostrils moved to the top of the cranium, becoming blowholes. Their front limbs became flippers (Basilosaurus, 35 million years ago). Their back legs shrank and eventually disappeared. This happened in the first toothed and baleen whales about 34 million years ago.

Whales also show convergent evolution. This is when unrelated animals develop similar features. The most obvious example is the streamlined, fish-like body. Other examples include echolocation, which helps them hunt in low light. Whales use the same kind of hearing as bats. Rorqual whales have jaw features like those of pelicans, which help them take in large mouthfuls of food.

Today, the closest living relatives of whales are hippopotamuses. They share a semi-aquatic ancestor that split from other artiodactyls some 60 million years ago. Around 40 million years ago, a shared ancestor split into cetaceans and anthracotheres. Nearly all anthracotheres died out by 2.5 million years ago. Only the hippopotamus line remained.

Biology

Whales have bodies shaped like torpedoes. Their necks cannot bend, and their flippers are made from changed arm bones. Most whales have flat heads, but monodontids and ziphiids are different. Their teeth have cementum over dentine, and enamel is only found on the tips of the biggest whales. Baleen whales have whalebone, which is made of keratin, instead of teeth. Whales breathe through a blowhole. Most have a thick layer of blubber to keep them warm. Whales swim by moving their tail fin up and down. Some kinds of whales log on the surface of the water. Whales can dive deep because they slow their heartbeat and store oxygen in their haemoglobin and myoglobin. Their ears are built for life in the marine world. Toothed whales use a melon to make clicks. Whales have cone cells and a tapetum lucidum in their eyes. Toothed whales do not have olfactory lobes, so they probably cannot smell well. The blue whale is the largest animal on Earth.

Whales make sounds for many reasons. The humpback whale sings a whale song. Toothed whales use sonar, which can be very loud, up to 20,000 watts (+73 dBm or +43 dBw). Whales make clicks, which are used for sonar, and whistles, which are frequency modulated (FM) sounds used to talk to each other. Whales kept in captivity sometimes copy human speech. Whales can teach, learn, and work together. They have spindle neurons in parts of the brain that humans also have. Sperm whales have the largest brains of any animal on Earth, though scientists now compare brain size using an encephalisation quotient. Small whales blow bubble rings. The southern right whale lifts its tail above the water in a behaviour called "sailing." Most whales have one calf each year, and the calf relies on its mother for one to two years. Whales sleep with one side of the brain at a time, so they can keep breathing.

Ecology

See also: Beluga whale § Predation

All whales eat meat. Toothed whales mostly eat fish and cephalopods, then crustaceans and bivalves. Baleen whales mostly eat krill and plankton, then crustaceans and other invertebrates. Some whales eat only one kind of food. The blue whale eats almost only krill. The minke whale eats mainly schooling fish. The sperm whale mostly eats squid. Grey whales eat animals that live on the ocean floor. Most whales hunt alone, but some hunt together in small groups. Large whales are not usually hunted. Smaller whales are sometimes hunted by orcas. Polar bears and other pagophilic animals also hunt small Arctic whales. Some whales gather in groups to stay safe. When they are at sea, they dive deep to stay away from orcas.

A 2010 study said whales help ocean fish. This has been called a "whale pump." Whales carry nutrients, such as nitrogen, from the deep ocean back up to the surface. Whales release waste at the surface. Their waste is rich in iron and nitrogen, which helps phytoplankton grow.

When a whale dies, its body sinks to the deep ocean and becomes a home for many sea creatures. A whale fall supports a rich group of living things, with 407 species found around the world. This is similar to other neritic hotspots, such as cold seeps and hydrothermal vents. A whale body breaks down in three stages. First, sharks and hagfish eat the soft tissues over months, or up to two years. Next, crustaceans and polychaetes live on the bones for several years. Finally, bacteria release hydrogen sulfide. This helps chemoautotrophic organisms grow, and these support animals such as mussels, clams, limpets, and sea snails for decades.

Relationship with humans

Main articles: Whaling and History of whaling

Humans have hunted whales since the Stone Age. Ancient whalers used harpoons to spear large whales from boats at sea. People hunted whales for their meat and blubber. Some Indigenous groups used baleen and bones to make tools and other items. The Basques went whaling as early as the 11th century. In the 16th century, they sailed as far as Newfoundland to hunt right whales. In the 1700s and 1800s, whalers mainly hunted for oil and baleen or whalebone. Baleen was used to make things such as corsets and skirt hoops. Whalers also sought ambergris, which was used in perfumes. Commercial whaling slowed down after the International Whaling Commission (IWC) placed a moratorium in 1982. This set a catch limit for each country.

Whales are also harmed in indirect ways. Some get caught in fishing nets as bycatch. Gillnetting and Seine netting cause many whale deaths. Marine pollution and organic chemicals build up in whales because they eat other animals high in the food chain. These chemicals can cause gastrointestinal cancers. Military sonar can affect how whales echolocate. It can also cause decompression sickness and has led to mass strandings. Ships sometimes hit whales, which is a serious danger to the North Atlantic right whale. From 2013 to at least 2023, Chile had the most registered whale-ship collisions in the world.

Whaling dropped after 1946. That year, the IWC set catch limits for each country because whale numbers were falling. Indigenous groups were not included in these limits until 2004. Some species, such as grey whales, have recovered. However, the North Atlantic population is functionally extinct. The IWC has set up two whale sanctuaries: the Southern Ocean Whale Sanctuary and the Indian Ocean Whale Sanctuary. The IWC recognizes at least 86 cetacean species. Several are at risk. The North Atlantic right whale is "Critically Endangered," and the fin and sperm whales are "Vulnerable." Many species are "Data Deficient," which means there is not enough information about them. Whales living in polar areas are affected by climate change. Millions of people go whale watching each year. Rules have been made to reduce disturbance to whales.

Whales have also shaped art and beliefs. The Norse and many coastal peoples made art about them. This includes the rorquals shown in Bangudae, South Korea. The Pacific Islanders and Aboriginal Australians saw whales as bringers of good things and joy, though French Polynesia is an exception. Whale gods were worshipped in parts of China, Korea and Vietnam. Buddhism shaped some of these beliefs. The Bryde's whale is called "grandfather fish" by Thai fishermen, who do not hunt it. The story of Jonah and the great fish appears in the Qur'an and the Book of Jonah. It is also mentioned in Matthew. Whales appear in books, such as Herman Melville's Moby Dick, and in films like Whale Rider.

In 1896, the Pall Mall Gazette helped spread an alternative medicine idea. The idea was about climbing inside a whale carcass to ease rheumatism. Belugas were the first whales kept in captivity. The first one was shown at Barnum's Museum in New York City in 1861. The Russian Navy also trained belugas for antimining work.