Cat Breeding Tips: Responsible Practices for Success and Well-being

 The blue whale (Balaenoptera musculus) is a marine mammal and a baleen whale. Reaching a maximum confirmed length of 29.9 meters (98 ft) and weighing up to 199 tonnes (196 long tons; 219 short tons), 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 dorsally 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 (the pygmy blue whale) in the Indian Ocean and South Pacific Ocean, and B. m. indica in the Northern Indian Ocean. There is also a population in the waters off Chile that may constitute a fifth subspecies.

In general, blue whale populations migrate between their summer feeding areas near the poles and their winter breeding grounds near the tropics. There is also evidence of year-round residencies, and partial or age/sex-based migration. Blue whales are filter feeders; their diet consists almost exclusively of krill. They are generally solitary or gather in small groups, and have no well-defined social structure other than mother–calf bonds. The fundamental frequency for blue whale vocalizations ranges from 8 to 25 Hz and the production of vocalizations may vary by region, season, behavior, and time of day. Orcas are their only natural predators.

The blue whale was once abundant in nearly all the Earth's oceans until the end of the 19th century. It was hunted almost to the point of extinction by whalers until the International Whaling Commission banned all blue whale hunting in 1966. The International Union for Conservation of Nature has listed blue whales as Endangered as of 2018. It continues to face numerous man-made threats such as ship strikes, pollution, ocean noise, and climate change.

Taxonomy See also: Evolution of cetaceans Nomenclature The genus name, Balaenoptera, means winged whale, while the species name, musculus, could mean "muscle" or a diminutive form of "mouse", possibly a pun by Carl Linnaeus when he named the species in Systema Naturae. One of the first published descriptions of a blue whale comes from Robert Sibbald's Phalainologia Nova, after Sibbald found a stranded whale in the estuary of the Firth of Forth, Scotland, in 1692. The name "blue whale" was derived from the Norwegian blåhval, coined by Svend Foyn shortly after he had perfected the harpoon gun. The Norwegian scientist G. O. Sars adopted it as the common name in 1874.

Blue whales were referred to as "Sibbald's rorqual", after Robert Sibbald, who first described the species. Herman Melville called the blue whale "sulphur bottom" in his novel Moby Dick because of the accumulation of diatoms creating a yellowish appearance on their pale underside.

Evolution

A phylogenetic tree of six baleen whale species Blue whales are rorquals in the family Balaenopteridae. A 2018 analysis estimates that the Balaenopteridae family diverged from other families in between 10.48 and 4.98 million years ago during the late Miocene. The earliest discovered anatomically modern blue whale is a partial skull fossil found in southern Italy, dating to the Early Pleistocene, roughly 1.5–1.25 million years ago. The Australian pygmy blue whale diverged during the Last Glacial Maximum. Their more recent divergence has resulted in the subspecies having a relatively low genetic diversity, and New Zealand blue whales have an even lower genetic diversity.

Whole genome sequencing suggests that blue whales are most closely related to sei whales with gray whales as a sister group. This study also found significant gene flow between minke whales and the ancestors of the blue and sei whale. Blue whales also displayed high genetic diversity.

Hybridization Blue whales are known to interbreed with fin whales. The earliest description of a possible hybrid between a blue and fin whale was a 20-meter (65 ft) anomalous female whale with the features of both the blue and the fin whales taken in the North Pacific. A whale captured off northwestern Spain in 1984, was found to have been the product of a blue whale mother and a fin whale father.

Two live blue-fin whale hybrids have since been documented in the Gulf of St. Lawrence (Canada), and in the Azores (Portugal). DNA tests done in Iceland on a blue whale killed in July 2018 by the Icelandic whaling company Hvalur hf, found that the whale was the offspring of a male fin whale and female blue whale; however, the results are pending independent testing and verification of the samples. Because the International Whaling Commission classified blue whales as a "Protection Stock", trading their meat is illegal, and the kill is an infraction that must be reported. Blue-fin hybrids have been detected from genetic analysis of whale meat samples taken from Japanese markets. Blue-fin whale hybrids are capable of being fertile. Molecular tests on a 21-meter (70 ft) pregnant female whale caught off Iceland in 1986 found that it had a blue whale mother and a fin whale father, while its fetus was sired by a blue whale.

In 2024, a genome analysis of North Atlantic blue whales found evidence that approximately 3.5% of the blue whales' genome was derived from hybridization with fin whales. The gene flow was determined to be unidirectional from fin to blue whales. Comparison with Antarctic blue whales showed that this hybridization began after the northern and southern populations had become separated. Despite their smaller size, fin whales have similar cruising and sprinting speeds to blue whales, which would allow fin males to complete courtship chases with blue females.

There is a reference to a humpback–blue whale hybrid in the South Pacific, attributed to marine biologist Michael Poole.

Subspecies and stocks At least four subspecies of blue whale are recognized, some of which are divided into population stocks or "management units". They have a worldwide distribution, but are mostly absent from the Arctic Ocean and the Mediterranean, Okhotsk, and Bering Sea.

Aerial photograph of an adult blue whale showing its length Aerial view of adult blue whale Northern subspecies (B. m. musculus) North Atlantic population – This population is mainly documented from New England along eastern Canada to Greenland, particularly in the Gulf of St. Lawrence, during summer though some individuals may remain there all year. They also aggregate near Iceland and have increased their presence in the Norwegian Sea. They are reported to migrate south to the West Indies, the Azores and northwest Africa. Eastern North Pacific population – Whales in this region mostly feed off California's coast from summer to fall and then Oregon, Washington State, the Alaska Gyre and Aleutian Islands later in the fall. During winter and spring, blue whales migrate south to the waters of Mexico, mostly the Gulf of California, and the Costa Rica Dome, where they both feed and breed. Central/Western Pacific population – This stock is documented around the Kamchatka Peninsula during the summer; some individuals may remain there year-round. They have been recorded wintering in Hawaiian waters, though some can be found in the Gulf of Alaska during fall and early winter. Northern Indian Ocean subspecies (B. m. indica) – This subspecies can be found year-round in the northwestern Indian Ocean, though some individuals have recorded travelling to the Crozet Islands during between summer and fall. Pygmy blue whale (B. m. brevicauda) Madagascar population – This population migrates between the Seychelles and Amirante Islands in the north and the Crozet Islands and Prince Edward Islands in the south were they feed, passing through the Mozambique Channel. Australia/Indonesia population – Whales in this region appear to winter off Indonesia and migrate to their summer feeding grounds off the coast of Western Australia, with major concentrations at Perth Canyon and an area stretching from the Great Australian Bight and Bass Strait. Eastern Australia/New Zealand population – This stock may reside in the Tasman Sea and the Lau Basin in winter and feed mostly in the South Taranaki Bight and off the coast of eastern North Island. Blue whales have been detected around New Zealand throughout the year. Antarctic subspecies (B. m. intermedia) – This subspecies includes all populations found around the Antarctic. They have been recorded to travel as far north as eastern tropical Pacific, the central Indian Ocean, and the waters of southwestern Australia and northern New Zealand. Blue whales off the Chilean coast may be a separate subspecies based on geographic separation, genetics, and unique song types. Chilean blue whales may overlap in the Eastern Tropical Pacific with Antarctica blue whales and Eastern North Pacific blue whales. Chilean blue whales are genetically differentiated from Antarctica blue whales and are unlikely to be interbreeding. However, the genetic distinction is less with the Eastern North Pacific blue whale and there may be gene flow between hemispheres.

Description

A blue whale with its bow wave, showing the blowhole The blue whale is a slender-bodied cetacean with a broad U-shaped head; thin, elongated flippers; a small 33 centimeters (13 in) sickle-shaped dorsal fin located close to the tail, and a large tail stock at the root of the wide and thin flukes. The upper jaw is lined with 70–395 black baleen plates. The throat region has 60–88 grooves which allows the skin to expand during feeding. The tongue can weigh 2.7 tonnes (3.0 short tons; 2.7 long tons) and the mouth is large enough to hold up to 90 tonnes (99 short tons; 89 long tons) of food and water.

The blue whale is the largest animal known to have ever existed. Long and streamlined, blue whales in the Northern Hemisphere average 23–24 m (75–79 ft) long and those in the Southern Hemisphere 24–25 m (79–82 ft). Typically, females are larger than males. The larger individuals of each subspecies weigh 72–135 t (71–133 long tons; 79–149 short tons). The maximum recorded weight was 190 t (187 long tons; 209 short tons) for a Southern Hemisphere female in 1947. The maximum confirmed length is 29.9 meters (98 ft) for a Southern Hemisphere female captured in 1909. The longest estimated length is 33 meters (108 ft) for a Southern Hemisphere female captured in 1922, though this measurement may have been unreliable.

The blue whale's skin is light bluish-gray with a thin layer of microorganisms, giving it a mottled look. The baleen plates are black and around 1 m (3.3 ft) long. The upper parts of the flippers are gray with the edges and undersides white, while the tail stock is light gray with a black and white underside. A distinctive trait of the blue whale is a splash of lighter color on the upper right side of the tail stock just in front of the tail flukes. Blue whales are often lighter underneath, but can appear uniformly light gray or beige after death. They are often plainly colored compared to other rorquals and are the only true blue cetacean.

Behavior and life history Blue whales are filter feeders. Most of their diet consists of krill. One individual can consume up to 40 million krill per day, around 3,600 kg (7,900 lb) of food. Blue whales hunt for food using lunge feeding, which involves accelerating towards a group of prey, opening their mouths and gulping them along with water. They feed by expanding the throat grooves, which allows them to take in more water. During the process, 90% of the blue whale's metabolic rate is expended. Blue whales most often feed at 100 meters (330 ft) deep during the day and only at night in surface waters. Foraging dives last around 10 minutes, though they can last up to 20 minutes. Blue whales typically eat twice a day during the feeding season.

Reproduction A blue whale's blow can be up to 12 m (39 ft) tall Blue whales have a long and slender body with mottled gray skin Blue whale mother and calf Blue whale mating season occurs during the winter. Males will follow a female and take turns getting close to her. If she surfaces to breathe, the males will attempt to escort her. After 10 months, the pregnant female will give birth to a calf at her breeding grounds. Newborn blue whales are typically 6–7 m (20–23 ft) long and weigh 2.3–3.6 tonnes (2.5–4.0 short tons; 2.3–3.5 long tons). The calf drinks 380–570 liters (100–150 US gal) of milk a day. Weaning occurs at around six months when the calf has doubled its length. Sexual maturity in blue whales happens at ages 5–10 for both sexes. Blue whales may live for at least 80 years and potentially over 100 years.

Migration Most blue whale populations migrate between summer feeding grounds in temperate or polar waters and winter breeding grounds in tropical waters. The migrations are generally poleward in spring and towards the Equator in autumn. Blue whales may follow leading whales that use their long-distance low-frequency sounds for navigation. Blue whales may also be found at their feeding grounds year-round.

Vocalizations A spectral display shows the first two phrases in a blue whale call A blue whale recorded near Cortes Bank, off the coast of Southern California Blue whales produce a variety of sounds including clicks, whistles, and pulses. The most common sounds are the long and patterned series of pulses, moans, and groans. Blue whales produce sounds with a fundamental frequency between 8–25 Hz. These sounds can be extremely loud and reach up to 188 decibels. They can be heard over distances of several hundred kilometers in good conditions. Blue whale vocalizations may play a role in communication, navigation, and locating prey.

Distribution and habitat Blue whale populations are mostly found in deep, open ocean waters. The specific habitats can vary based on regional characteristics. In general, they prefer colder waters for feeding and warmer tropical waters for breeding and calving.

Conservation status Blue whales are listed as Endangered on the IUCN Red List. The primary threats to their survival include ship strikes, entanglement in fishing gear, pollution, and the impacts of climate change on their food supply and habitat. Conservation efforts include international agreements to protect whale populations, regulations to reduce ship strikes and fishing gear entanglements, and monitoring and research programs to better understand blue whale behavior and ecology.