Balaenoptera musculus
The blue whale (Balaenoptera musculus), also known as the blue whale, is a species of cetacean Mystice of the Balaenopteridae family. Its average size is between 24 and 27 meters in length and weigh between 100 and 120 tons, although there are records of specimens of more than 30 m in length and 170 t in weight, which make it the largest animal on planet Earth., not only currently but also the largest on record in the history of life on Earth.
Long and slender, the body of this marine mammal is bluish-grey along the back and slightly lighter ventrally. There are at least three distinct subspecies: B. m. musculus, from the North Atlantic and North Pacific; B. m. intermedia, from the Antarctic Ocean and B. m. brevicauda (also known as the pygmy blue whale), found in the Indian Ocean and the South Pacific. There are doubts about the validity of a fourth subspecies, B. m. indica, which is also found in the Indian Ocean. Like other baleen whales, their diet consists mainly of small crustaceans known as krill.
Blue whales were abundant in almost all oceans until the early 20th century. For more than forty years they were hunted to near extinction, prompting their protection by the international community in 1966. A 2002 report estimated their number between 5,000 and 12,000 worldwide, located in at least five groups, although more recent research on the pygmy subspecies suggests that these data may be an underestimate. Before the start of commercial whaling, the largest population was in Antarctica, with around 239,000 (between 202,000 and 311,000). Currently only much smaller concentrations (of about 2,000 individuals) remain in the northeast Pacific, Antarctic, and Indian Oceans. There are two more groups in the North Atlantic and at least two in the southern hemisphere.
Taxonomy
Although all mysticetes are usually called "whales", there are those who reserve this name for the Balaenidae family and call the species of the Balaenopteridae family "rorquals", a family that includes, in addition to the blue whale, the humpback, the fin whale, Bryde's whale, northern minke, minke whale, minke whale, tropical whale and Omura's whale. The family Balaenopteridae is thought to have diverged from other families of the suborder Mysticeti as early as the middle Oligocene; However, it is unknown when the members of that family separated from each other. The blue whale is normally classified as one of eight fin whale species included in the genus Balaenoptera, and although one authority classified it in a separate genus, Sibbaldus, this classification was not accepted by anyone else. Recent DNA sequencing analyzes indicate that it is phylogenetically closest to the northern minke whale (Balaenoptera borealis) and Bryde's whale (Balaenoptera brydei) than other members of the family Balaenoptera, and closer to the humpback (Megaptera) and gray whale (Eschrichtius) than to fin whales (Balaenoptera acutorostrata) and southern (Balaenoptera bonaerensis) whales. If future research confirms these relationships, it would be necessary to reclassify the whales.
There are documented cases of hybrids between this species and fin whales in the wild, but the reproductive capacity of these hybrids is unknown. Arnason and Gullberg described the genetic distance between fin and blue whales as the same as exists between the human being and the gorilla.
The name of the species, musculus, comes from Latin and can be translated as "muscle", although it can also be translated as "little mouse". Linnaeus, who assigned that name to the blue whale in his Systema naturæ of 1758, he may have used a deliberate and ironic double meaning in giving it this name. (by Sir Robert Sibbald), great blue whale and great northern whale. These names fell out of use in recent decades.
Different authorities subdivided the species into four subspecies, one of which is doubtful:
- B. m. musculus (Linnaeus, 1758), North Blue Whale, including North Atlantic and North Pacific populations,
- B. m. intermediate (Burmeister, 1871), Antarctic blue whale, the largest one in the Antarctic Ocean,
- B. m. brevicauda (Ichihara, 1966), the pygmy blue whale, with populations in the Indian Ocean and in the South Pacific,
- and the most problematic B. m. indicates (Blyth, 1859), the great rorcual of India, which is also in the Indian Ocean and which, although described earlier, may be the same subspecies as the one that the B. m. brevicauda.
Description and behavior
It has a long, slender body that appears slender compared to the stockier build of other mysticetes. The head is large (approximately a quarter of its body), flat and U-shaped, with a crest running from the spiracles to the front end of the rostrum. The front of the mouth is thick with between 300 and 400 wattles on each side, each wattle about a meter in length, and hanging from the upper jaw; they are particularly broad (50 cm) in proportion to their length. They have between 55 and 88 grooves. (called ventral folds) along the throat and parallel to the body. These folds help the evacuation of water from the mouth after their "lunges" to feed. The dorsal fin (only visible briefly during the submersion sequence) is located at the beginning of the last quarter of the body and is small and variable in shape (triangular, rounded, slightly falcate, or just a small bulge). When it surfaces to breathing, it takes its back and the blowhole out of the water to a greater extent than other large mysticetes such as the fin whale or the northern whale. This feature can be used by observers to differentiate it from these species on the high seas. Before starting a maneuver to dive to a great depth, they usually take their caudal fin out of the water. When breathing on the surface, it emits a dense and spectacular jet of water vapor that can reach a height of between 6 and 12 m (generally around 9 m), which can be seen from a great distance on a calm sea day. Their lung capacity is 5,000 litres. Like all mysticetes, they have a double blowhole, protected anteriorly and laterally by a larger prominence than in other rorquals.
The pectoral fins are pointed in shape and three to four meters long, with the upper part gray with a thin white border and the underside white. The head and tail fin are usually uniformly grey. The upperparts, and sometimes the fins, are usually mottled to a degree that varies considerably from individual to individual, and thus some may have a uniform slate-grey color all over the body, but others show considerable variation of dark blue, gray, and black, all with small spots along the entire body. Its belly often has a grayish or yellowish color, due to the rubbing of mysticetes with microorganisms called diatoms in the cold waters of the Antarctic, the North Pacific and the North Atlantic.
They can reach speeds of up to 50 km/h (27 knots) when threatened, although their normal travel speed is 22 km/h (12 knots). While feeding, their speed ranges from 2 to 6.5 km/h (1 - 3.5 knots).
They generally live alone or in pairs, although groups of up to seven individuals can be observed; where there are large concentrations of food, up to 60 specimens have been recorded together in the same area. However, they do not form the large groups that they are observed in other species of mysticetes. Determining gender by analyzing their DNA, a study found that adult blue whale pairs are generally made up of a male and a female, and have often been seen together for long periods, although some have also been found to males have mated with different females at different times.
Size and Mass
Due to their enormous size, they are difficult to weigh. Most blue whales caught by whaling ships were not weighed whole, but were first cut into more manageable pieces. This caused an underestimation of his total weight due to loss of blood and other fluids. Even taking the above into account, an adult specimen can measure between 24 and 27 meters in length and weigh between 100 and 120 tons. The largest specimen on record measured 33.63 m and the longest scientifically validated length was 29.9 m. The most massive was a female caught off South Georgia in 1947, which weighed 173 tons. Southern Hemisphere populations are generally larger than Northern Hemisphere populations and females are larger than males.
It is considered to be the most massive animal that has ever existed on planet Earth, surpassing in mass any extant or extinct terrestrial animal. The blue whale is heavier than the extinct Patagotitan mayorum, the largest of the dinosaurs, whose mass is estimated at 77 tons. It also surpasses the extinct fish Leedsichthys which may have come close to its size. Even allowing for the difficulty of finding complete fossils and that their weight can only be estimated, all of these animals would be smaller than the blue whale..
Its tongue weighs approximately 2.7 tons, and, when fully open, its mouth is large enough to hold up to 90 tons of food and water. Despite the size of its mouth, however, the The dimensions of its throat are such that a blue whale cannot swallow objects larger than a beach ball. The heart of the largest specimens can weigh 600 kg, making it the largest known of any animal. Its aorta is approximately 23 cm in diameter. At birth the calves measure between 7 and 8 m, and weigh up to 2,700 kg (the same as an adult hippopotamus).
Food
They feed almost exclusively on krill, although they will also ingest small amounts of copepods. The specific species of zooplankton they feed on varies from ocean to ocean; in the North Atlantic Meganyctiphanes norvegica, Thysanoessa raschii, Thysanoessa inermis and Thysanoessa longicaudata are their usual food; in the North Pacific, Euphausia pacifica, Thysanoessa spinifera, Thysanoessa raschii and Nyctiphanes symplex;, in the Antarctic, Euphausia superba, Euphausia crystallorophias and Euphausia valentin.
An adult can ingest up to 40 million krill in a day. They always feed in areas with the highest concentration of krill and can consume up to four tons of krill in a day during the peak feeding season. day, although there are reports of consumption of up to eight t. The energy requirements of an adult are around 1.5 million calories each day. They generally feed at depths of more than 100 m during the day and they only feed on the surface at night. Dives during their feeding are generally between five and fifteen minutes, although dives of up to twenty minutes are common and there are records of up to thirty-six minutes. The fin whale is carried out by a filtering system: in a "push" it opens its mouth introducing large amounts of water and krill, then it closes its jaws and pushes the water back out through its baleen, allowing the water to escape. come out while capturing the prey held in them. Although its diet is almost exclusively krill, it also incidentally consumes small fish, crustaceans, and squid that swim among it.
Life Cycle
Mating season begins in late autumn and continues until late winter. Little is known about mating behavior or breeding locations. Females generally give birth once every two to three years in early winter after a gestation period of ten to twelve months. The calf weighs nearly three tons and is about 7-8 m in length. Calves drink about three hundred and eighty liters of milk a day and gain about two hundred kilograms of weight each day as well. Weaning occurs at approximately eight months of age; at that time the calf has already doubled its length. Sexual maturity of males occurs at approximately five years of age, when they measure around 20–21 m, and that of females when they measure 21–23 m, also at five years old. Physical maturity for males in the Northern Hemisphere occurs when they reach 24 m in length, while females reach 25 m in length. Scientists estimate that blue whales can live to 80 years or older.
Strandings on the coast of these animals are very rare and, due to the social structure of the species, mass strandings are truly unusual. Therefore, when a stranding occurs, it becomes a focus of public interest. In 1920, a specimen ran aground near Bragar (Isle of Lewis) in the Outer Hebrides of Scotland. A whaling ship stuck a harpoon into it, but it failed to explode and the whale ended up on the coast. Two of the whale's bones were erected in Lewis and remain as a tourist attraction.
Vocalization
Blue whales emit powerful regular sounds at low frequencies particularly suitable for long-range underwater communication. Estimates by Cummings and Thompson (1971) suggest that the volume of sounds emitted by these whales is between 155 and 188 decibels. relative to 1 micropascal (µPa) at a reference distance of one meter. All groups emit calls at a fundamental frequency between 10 and 40 Hz, even reaching 9 Hz (the lowest frequency sound that humans can perceive, it is usually 20 Hz) and the highest recorded (probably from the pygmy subspecies) reached 524 Hz. They emit calls of at least 10 to 30 seconds duration. Off the coast of Sri Lanka they have been recorded repeatedly emitting four-note "songs" lasting approximately two minutes each, evoking the famous humpback songs. The researchers believe that since this phenomenon has not been observed in any other population, it may be a characteristic unique to subspecies B. m. brevicauda (pygmy).
The reasons that lead them to make these sounds are unknown. Richardson et al (1995) talks about six possible motives: interindividual distance maintenance, species and individual recognition, transmission of contextual information (for example: feeding, alarm, courtship, etc.), maintenance of social organization (for example: calls between males and females), location of topographic features or position of sources of possible prey.
Population and hunting
The hunting decades
They are difficult animals to capture or kill. Their size, speed, and strength meant that they were rarely in the crosshairs of early whaling ships, which primarily targeted sperm whales and right whales. In 1864 the Norwegian Svend Foyn equipped a steamship with purpose-designed harpoons. for hunting large cetaceans. Although initially unwieldy and had a low success rate, Foyn perfected the harpoon gun and soon several whaling stations were established off the coast of Finnmark in northern Norway. Due to disputes with local fishermen, the last whaling station in Finnmark was closed in 1904.
Hunting soon began in Iceland (1883), the Faroe Islands (1894), the island of Newfoundland (1898), Spitsbergen (1903) and the Georgias and South Sandwich Islands (1904-1905). After the introduction of steam-powered factory ships with ramps at the stern in 1925, the number of blue whales (and mysticetes in general) killed annually increased dramatically. Between 1930 and 1931 these ships hunted 29,400 specimens in the Antarctic region alone. Towards the end of the Second World War, its population had been considerably reduced and in 1946 the first quotas that restricted the international trade in mysticetes were introduced, although they were ineffective because they did not contemplate a differentiation between species. Thus, the rarest species could be hunted to the same extent as those that had a relatively abundant population. Their hunting was banned in the 1960s by the International Whaling Commission, and illegal whaling by the Soviet Union stopped in the 1970s, during which time 330,000 blue whales had been killed in the region. Antarctica, 33,000 in the rest of the Southern Hemisphere, 8,200 in the North Pacific, and 7,000 in the North Atlantic. The largest original group, that of the Antarctic region, was reduced to 0.15% of its initial population.
Whaling ships had driven this species almost to extinction, but instead of taking fewer individuals over a longer period, the whalers continued to deplete their population. In retrospect, if the whaling industry had allowed supervision and regulation by marine biologists, more cetaceans might have become commercially available, albeit over a longer period. The demographic dynamics involved in hunting marine mammals that reach advanced ages are completely different from those involved in catching fish with shorter life spans. Due to longer breeding periods (one year gestation) and smaller litter sizes (one or two calves), cetacean populations recover much more slowly than populations of smaller animals, which tend to spend less time and time. resources in younger individuals.
Population and current distribution
Since the introduction of the whaling ban, studies have failed to find out whether the global level of conservation of the species is increasing or remaining stable. In the Antarctic region, the most optimistic estimates show a significant increase of 7.3% per year since the end of the Soviet Union's illegal hunting, although their numbers still remain at less than 1% of levels prior to their commercial hunting. It has also been suggested that the Icelandic and Californian populations are increasing, but these increases are not statistically significant. The total world population was estimated to be between 5,000 and 12,000 in 2002, although with high levels of uncertainty in the estimates available for many areas. It is listed as an endangered species on the IUCN Red List of threatened species, and it has been like this since the creation of the list. In the case of the Antarctic subspecies (B. m. intermedia), the largest, its situation is even worse and it is qualified in the List Red by the IUCN as critically endangered. It is also listed on Appendix I (species threatened with extinction) of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). The highest known concentration of the species, with about 2,000 individuals, it is the Northeast Pacific population of the northern blue whale (B. m. musculus) a subspecies that ranges from Alaska to Costa Rica, but is usually sighted in California during the summer. Sometimes this population strays into the Northwest Pacific Ocean and infrequent sightings have been recorded between the Kamchatka Peninsula and the northern tip of Japan.
Two groups of subspecies B. m. muscle. The first is found in Greenland, Newfoundland and Labrador, Nova Scotia and the Gulf of St. Lawrence, with about 500 specimens. The second (the easternmost group was discovered in the Azores in spring and in Iceland in July and August) is supposed to follow the Mid-Atlantic Ridge between the two volcanic islands. Beyond Iceland, they have been discovered as far north as Spitsbergen and Jan Mayen, although such observations are rare. Scientists do not know where the rorquals spend their winters. The total North Atlantic population is estimated to be between 600 and 1,500 individuals.
In the Southern Hemisphere there appear to be two distinct subspecies, the Antarctic blue whale (B. m. intermedia) and the little-studied pygmy blue whale (B. m. brevicauda) found in the waters of the Indian Ocean. Recent research (mid-1998) provided an estimate of 2,280 individuals in the Southern Ocean, of which less than 1% were likely pygmy blue whales. Estimates from 1996 work put 424 pygmy whales in just one small area south of Madagascar, so it is likely that specimens in the entire Indian Ocean number in the thousands. If this is true, global populations would be higher than given by initial forecasts.
A fourth subspecies, the B. m. indica, was described by Blyth in 1859 in the North Indian Ocean, but difficulties in identifying distinctive features of this subspecies make it a synonym of B. m. brevicauda, the pygmy blue whale. It appears that Soviet catch records indicate that adult females are closer in size to pygmy whales than to B. m. musculus, although populations of B. m. indicates and B. m. brevicauda appear to be distinct and breeding seasons differ by almost six months.
The migratory routes of these subspecies are not yet well known. For example, there are records of pygmy whales in the North Indian Ocean (Oman, Maldives, Sri Lanka) where they may form a resident population. On the other hand, the population of blue whales found in Chile and Peru may also be a resident population. different. Some Antarctic blue whales come close to the eastern coast of the South Atlantic in winter, and occasionally their vocalizations are heard in Peru, Western Australia, and in the North Indian Ocean. In Chile, the Cetacean Conservation Center, with the support of the Chilean Navy, undertook important research and conservation work and are working on the study of a concentration of specimens recently discovered feeding on the coast of the Isla Grande de Chiloé in an area called the Gulf of Corcovado where 326 animals have been sighted near off the coast in the summer of 2007.
Efforts to make more precise population estimates are being carried out by scientists at Duke University, who maintain OBIS-SEAMAP, Ocean Biogeographic Information System - Spatial Ecological Analysis of Megavertebrate Populations (Ocean Biogeographic Information System - Spatial Ecological Analysis of Megavertebrate Populations), a compilation of marine mammal data from approximately 130 sources.
Other threats
Because of their enormous size, strength, and speed, adults have virtually no natural predators. The only known animal is the orca. There are documented reports of attacks by these animals, such as a study showing that in the Sea of Cortez no less than 25% of adult specimens had scars resulting from orca attacks and the death of a specimen in Baja California victim of its attack, as well as a report in the magazine National Geographic of an adult attacked by orcas where, although the orcas were unable to kill the animal during their attack, he suffered extensive and numerous injuries and likely died from them shortly after the attack. However, while killer whales have been shown to attack and can kill a blue whale, the mortality rate due to these attacks is unknown.
They can also be injured, sometimes fatally, by colliding with large vessels on the high seas and also by becoming entangled or caught in fishing nets. The continuing increase in human-produced ambient noise in the ocean, including sonar, drowns out the vocalizations produced by cetaceans, making it difficult for them to communicate. Human threats to the potential recovery of their population also include the accumulation of polychlorinated biphenyls (PCBs) and other chemicals that they ingest while feeding and that are transmitted to pups through mother's milk.
Global warming causes glaciers and permafrost to melt rapidly, leading to a large increase in the amount of freshwater in the oceans, and there is a risk of reaching a tipping point in that increase that could lead to a disturbance in the thermohaline circulation. Like most cetaceans, blue whales are migratory, spending the summer in cooler, high latitudes, where they feed in krill-rich waters; in winter they move to warmer, low latitudes, where they mate and give birth. Given that their migration patterns are based on ocean temperatures, a change in this circulation that moves warm and cold water around the globe it would likely have effects on their migration. Changing ocean temperatures would also affect their food supply, as warming would cause a decrease in salinity levels that would cause a significant change in krill status and abundance.