Blue whale

Nomenclature The genus name, Balaenoptera, means winged whale, 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. This tinge is due to a coating of huge numbers of diatoms. The earliest discovered anatomically modern blue whale is a partial skull fossil from southern Italy identified as B. cf. musculus, 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. The earliest description of a possible hybrid between a blue whale and a fin whale was a 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 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. Gene flow was found to be unidirectional from fin whales to blue whales. Comparison with Antarctic blue whales showed that this hybridization began after the separation of the northern and southern populations. 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 traditionally recognized, some of which are divided into population stocks or "management units". Like many large rorquals, the blue whale is a cosmopolitan species. They have a worldwide distribution, but are mostly absent from the Arctic Ocean and the Mediterranean, Okhotsk, and Bering Sea. Chilean blue whales might 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 such that interbreeding is unlikely. However, the genetic distinction is less between them and the Eastern North Pacific blue whale, hence there might be gene flow between the Southern and Northern Hemispheres. A 2019 study by Luis Pastene, Jorge Acevedo and Trevor Branch provided new morphometric data from a survey of 60 Chilean blue whales, hoping to address the debate about the possible distinction of this population from others in the Southern Hemisphere. Data from this study, based on whales collected in the 1965/1966 whaling season, shows that both the maximum and mean body length of Chilean blue whales lies between these values in pygmy and Antarctic blue whales. Data also indicates a potential difference in snout-eye measurements between the three, and a significant difference in fluke-anus length between the Chilean population and pygmy blue whales. This further confirms Chilean blue whales as a separate population, and implies that they do not fall under the same subspecies as the pygmy blue whale (B. m. brevicauda). A 2024 genomic study of the global blue whale population found support for the subspecific status of Antarctic and Indo-western Pacific blue whales but not eastern Pacific blue whales. The study found "...divergence between the eastern North and eastern South Pacific, and among the eastern Indian Ocean, the western South Pacific and the northern Indian Ocean." and "no divergence within the Antarctic". ==Description==

, showing the blowholes The blue whale is a slender-bodied cetacean with a broad U-shaped head; thin, elongated flippers; a small 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 70–400 black baleen plates less than in length. The throat region has 60–88 grooves which allows the skin to expand during feeding. It has two blowholes that can squirt up in the air. The mottling patterns near the dorsal fin vary between individuals. The underbelly has lighter pigmentation and can appear yellowish due to diatoms in the water, Size measuring The blue whale is the largest animal known ever to have existed. Some studies have estimated that certain shastasaurid ichthyosaurs and the ancient whale Perucetus could have rivalled the blue whale in size, with Perucetus actually being heavier with a mean weight of . However, these estimates were based on fragmentary remains, and the proposed size for Perucetus was disputed by studies in 2024. Other studies estimate that, on land, large sauropods like Bruhathkayosaurus (mean weight: 110–170 tons) and Maraapunisaurus (mean weight: 80–120 tons) might have rivalled the blue whale, with the former even exceeding the blue whale based on its most liberal estimates (240 tons). However, these estimates were based on even more fragmentary specimens that had disintegrated by the time estimates could be made. The International Whaling Commission (IWC) whaling database reports 88 individuals longer than , including one of . The record length was measured at . The longest scientifically measured individual blue whale was from rostrum tip to tail notch. Female blue whales are larger than males. Hydrodynamic models suggest a blue whale could not exceed because of metabolic and energy constraints. The existence of blue whales exceeding in length has been questioned. Length measurements of blue whales in the Gulf of California suggest a mean length of and a maximum length of , which is comparable to Northeast Pacific blue whales. The maximum length of the individual is estimated by another estimate to be between , with a probability of 0.95. In the Northern Hemisphere, males weigh an average and females . Eastern North Pacific blue whale males average and females . Antarctic males average and females . Pygmy blue whale males average to . The average weight of an adult blue whale is between . The brain of a blue whale, which weighed , weighed about . The male blue whale has the largest penis in the animal kingdom, at around long and wide. The oldest blue whale discovered using this method was found to be 110 years old. The maximum age of a pygmy blue whale determined this way is 73 years. Long-term identification studies in the Northeast Pacific suggest that they live for at least 40–45 years. In a female pygmy blue whale, one corpus albicans is formed on average every 2.6 years. ==Behavior and ecology==

The blue whale is usually solitary, but can be found in pairs. When productivity is high enough, blue whales can be seen in gatherings of more than 50 individuals. The animals appear to use memory to locate the best feeding areas. There is evidence of alternative strategies, such as year-round residency, and partial (where only some individuals migrate) or age/sex-based migration. Some whales have been recorded feeding in breeding grounds. Blue whale typically swim at but may swim faster at during encounters with boats, predators or other individuals. However, it is unclear whether the blue whale can actually reach a speed of , and the most reliably reported maximum speed was . Their massive size limits their ability to breach. The greatest dive depth reported from tagged blue whales was . however, the longest dive measured was 15.2 minutes. A blue whale's heart rate can drop to 2 beats per minute (bpm) at deep depths, but upon surfacing, can rise to 37 bpm, which is close to its peak heart rate. Diet and feeding The blue whale's diet consists almost exclusively of krill, which they capture through lunge feeding, where they swim towards krill at high speeds with their mouths open up to 80 degrees. They squeeze the water out through their baleen plates with pressure from the throat pouch and tongue, and swallow the remaining krill. Blue whales have been recorded making 180° rolls during lunge-feeding, possibly allowing them to search the prey field and find the densest patches. While pursuing krill patches, blue whales maximize their calorie intake by increasing the number of lunges while selecting the thickest patches. This provides them enough energy for everyday activities while storing additional energy necessary for migration and reproduction. Due to their size blue whales have larger energetic demands than most animals, resulting in their need for this specific feeding habit. Blue whales have to engulf densities greater than 100 krill/m3 to maintain the cost of lunge feeding. They can consume from one mouthful of krill, which can provide up to 240 times more energy than used in a single lunge. On average, a blue whale eats each day. In California, they feed mostly on Thysanoessa spinifera, but also less commonly on North pacific krill (Euphausia pacifica). Research of the Eastern North Pacific population shows that when diving to feed on krill, the whales reach an average depth of 201 meters, with dives lasting 9.8 minutes on average. Different whale species select different feeding spaces and times as well as different prey species. In the Southern Ocean, baleen whales appear to feed on Antarctic krill of different sizes, which may lessen competition between them. Blue whale feeding habits may differ due to situational disturbances, like environmental shifts or human interference. This can cause a change in diet due to stress response. Due to these changing situations, there was a study performed on blue whales measuring cortisol levels and comparing them with the levels of stressed individuals, it gave a closer look to the reasoning behind their diet and behavioral changes. Reproduction and birth The age of sexual maturity in blue whales is thought to be between 5 and 15 years, In the Northern Hemisphere, the length at which they reach maturity is for females and for males. In the Southern Hemisphere, the length of maturity is and for females and males respectively. Female pygmy blue whales are in length Since corpora are added every ~2.5 years after sexual maturity, physical maturity is assumed to occur at 35 years. Little is known about mating behavior, or breeding and birthing areas. A male blue whale typically trails a female and will fight off potential rivals. The species mates from fall to winter. amounting to 60% of their overall body weight throughout summer foraging periods. Gestation may last 10–12 months with calves being long and weighing at birth. The first video of a calf thought to be nursing was filmed in New Zealand in 2016. Calves may be weaned when they reach 6–8 months old at a length of . Vocalizations Blue whales produce some of the loudest and lowest frequency vocalizations in the animal kingdom, The fundamental frequency for blue whale vocalizations ranges from 8 to 25 Hz. The maximum loudness is 188 dB. Vocalizations produced by the Eastern North Pacific population have been well studied. This population produces pulsed calls ("A") and tonal calls ("B"), upswept tones that precede type B calls ("C") and separate downswept tones ("D"). A and B calls are often produced in repeated co-occurring sequences and sung only by males, suggesting a reproductive function. D calls may have multiple functions. They are produced by both sexes during social interactions while feeding. and by males when competing for mates. A blue whale call recorded off Madagascar, a two-unit phrase, consists of 5–7 pulses with a center frequency of 35.1 ± 0.7 Hz lasting 4.4 ± 0.5 seconds proceeding a 35 ± 0 Hz tone that is 10.9 ± 1.1 seconds long. There is evidence that some blue whale songs have temporally declined in tonal frequency. The vocalization of blue whales in the Eastern North Pacific decreased in tonal frequency by 31% from the early 1960s to the early 21st century. tracing "more than six years of acoustic monitoring" off of California, researchers found that during a heatwave, the blue whales were vocalizing less often, potentially due to needing to spend their energy trying to find food that is increasingly scarce due to the effects of climate change. A June 2022 study suggested that the decline in song frequency in blue whales is simply a cultural phenomenon. Off southeastern Australia, 3.7% of blue whales photographed had rake marks and 42.1% of photographed pygmy blue whales off Western Australia had rake marks. A blue whale mother and calf were first observed being chased at high speeds by orcas off southeastern Australia. The first documented attack occurred in 1977 off southwestern Baja California, Mexico, but the injured whale escaped after five hours. Four more blue whales were documented as being chased by a group of orcas between 1982 and 2003. In September 2003, a group of orcas in the Eastern Tropical Pacific was encountered feeding on a recently killed blue whale calf. In March 2014, a commercial whale watch boat operator recorded an incident involving a group of orcas harassing a blue whale in Monterey Bay. The blue whale defended itself by slapping its tail. A similar incident was recorded by a drone in Monterey Bay in May 2017. The first direct observations of orca attacks occurred off the south coast of Western Australia, two in 2019 and one more in 2021. The first victim was estimated to be an adult between . Infestations and health threats In Antarctic waters, blue whales accumulate diatoms of the species Cocconeis ceticola and the genera Navicola, which are normally removed when the whales enter warmer waters. Barnacles such as Coronula diadema, Coronula reginae, and Cryptolepas rhachianecti, latch on to whale skin deep enough to leave behind a pit if removed. Whale lice species make their home in cracks of the skin and are relatively harmless. The copepod species Pennella balaenopterae digs in and attaches itself to the blubber to feed on. Intestinal parasites include the trematode genera Ogmogaster and Lecithodesmus; the tapeworm genera Priapocephalus, Phyllobotrium, Tetrabothrius, Diphyllobotrium, and Diplogonoporus; and the thorny-headed worm genus Bolbosoma. In the North Atlantic, blue whales also contain the protozoans Entamoeba, Giardia and Balantidium. ==Conservation==

The global blue whale population is estimated to be 5,000–15,000 mature individuals and 10,000–25,000 total as of 2018. The protected status of North Atlantic blue whales was not recognized by Iceland until 1960. In the United States, the species is protected under the Endangered Species Act. and the IUCN Red List. and the Convention on the Conservation of Migratory Species of Wild Animals. Although, for some populations, there is not enough information on current abundance trends (e.g., pygmy blue whales), others are critically endangered (e.g., Antarctic blue whales). Threats platform In 2017, DNA evidence was used to identify whale bones at Icelandic archaeological sites. Of the 124 bones analyzed more than 50% were from blue whales and some dated as far back as 900 CE. This, and other evidence, suggests that Icelanders were hunting whales as early as the 9th century, just as the settlement of Iceland began. Thus Icelanders would have been among the earliest known humans to hunt the blue whale. Blue whales were initially difficult to hunt because of their size and speed. Blue whale whaling peaked between 1930 and 1931 with 30,000 animals taken. Harvesting of the species was particularly high in the Antarctic, with 350,000–360,000 whales taken in the first half of the 20th century. In addition, 11,000 North Atlantic whales (mostly around Iceland) and 9,500 North Pacific whales were killed during the same period. However, the Soviet Union continued to illegally hunt blue whales and other species up until the 1970s. Ship strikes are a significant mortality factor for blue whales, especially off the U.S. West Coast. A total of 17 blue whales were killed or suspected to have been killed by ships between 1998 and 2019 off the U.S. West Coast. Lethal ship strikes are also a problem in Sri Lankan waters, where their habitat intersects with one of the world's most active shipping routes. Here, strikes caused the deaths of eleven blue whales in 2010 and 2012, and at least two in 2014. Ship-strike mortality claimed the lives of two blue whales off southern Chile in the 2010s. Possible measures for reducing future ship strikes include better predictive models of whale distribution, changes in shipping lanes, vessel speed reductions, and seasonal and dynamic management of shipping lanes. Few cases of blue whale entanglement in commercial fishing gear have been documented. The first report in the U.S. occurred off California in 2015, reportedly some type of deep-water trap/pot fishery. Three more entanglement cases were reported in 2016. In Sri Lanka, a blue whale was documented with a net wrapped through its mouth, along the sides of its body, and wound around its tail. Increasing man-made underwater noise impacts blue whales. They may be exposed to noise from commercial shipping and seismic surveys as a part of oil and gas exploration. Blue whales in the Southern California Bight decreased calling in the presence of mid-frequency active (MFA) sonar. Exposure to simulated MFA sonar was found to interrupt blue whale deep-dive feeding, but no changes in behavior were observed in individuals feeding at shallower depths. The responses also depended on the animal's behavioral state, its (horizontal) distance from the sound source and the availability of prey. The potential impacts of pollutants on blue whales is unknown. However, because blue whales feed low on the food chain, there is a lesser chance for bioaccumulation of organic chemical contaminants. Analysis of the earwax of a male blue whale killed by a collision with a ship off the coast of California showed contaminants like pesticides, flame retardants, and mercury. Reconstructed persistent organic pollutant (POP) profiles suggested that a substantial maternal transfer occurred during gestation and/or lactation. Male blue whales in the Gulf of St. Lawrence, Canada, were found to have higher concentrations of PCBs, dichlorodiphenyltrichloroethane (DDT), metabolites, and several other organochlorine compounds relative to females, reflecting maternal transfer of these persistent contaminants from females into young. == See also ==