The Antarctic minke whale, also called the southern minke whale (Balaenoptera bonaerensis), is a type of minke whale in the group of baleen whales. It is the second smallest rorqual and the third smallest baleen whale. Scientists first studied this whale in the 1800s, but it was not recognized as a separate species until the 1990s. Because it is small and produces little oil, the whaling industry largely ignored it. This helped the Antarctic minke whale avoid the decline faced by other baleen whales, allowing its population to remain large into the 21st century, with hundreds of thousands of individuals. Today, it is the most common baleen whale in the world and plays a key role in the whaling industry, along with the common minke whale. The Antarctic minke whale lives mainly in the Southern Hemisphere, though some have been seen in the North Atlantic. It primarily eats euphausiids.
Taxonomy
In February 1867, a fisherman found a male rorqual whale about 9.75 meters (32 feet) long floating in the Río de la Plata near Belgrano, about ten miles from Buenos Aires, Argentina. After taking the whale to land, he showed it to Hermann Burmeister, a German zoologist living in Argentina. Burmeister named the whale a new species, Balaenoptera bonaerensis, the same year. In 1873, a skeleton of another whale, 4.7 meters (15 feet) long, was found off Otago Head, New Zealand. Professor Frederick Hutton, who worked at the Otago Museum, sent the skeleton to the British Museum in London. There, John Edward Gray, a British zoologist, examined it and named it B. huttoni, a new type of "pike whale" (now known as minke whale, B. acutorostrata). These descriptions were not widely accepted for about 100 years.
In the 1950s, Gordon R. Williamson studied three whales from the Southern Hemisphere. He examined a pregnant female caught in 1955 and two males caught in 1957, all taken aboard the British ship Balaena. These whales had pale gray flippers and baleen with white plates at the front and gray plates at the back. Studies in the 1960s supported his findings. In the 1970s, scientists compared the whales' bones and physical features and suggested they might be a subspecies of the common minke whale, named B. a. bonaerensis after Burmeister’s original specimen. By the 1980s, more research based on appearance and bones showed there were two forms in the Southern Hemisphere: a larger type with dark flippers and a smaller type with white flippers. The smaller type appeared more closely related to the common minke whale in the Northern Hemisphere. Genetic studies using DNA analysis later confirmed there were at least two species of minke whale: B. acutorostrata and B. bonaerensis. One study even suggested sei whales and a type of Bryde’s whale were more closely related to each other than to either minke whale species. Dale W. Rice, an American scientist, supported these findings in his work on marine mammals. He gave the Antarctic minke whale (B. bonaerensis) full species status, and the International Whaling Commission later agreed. Other organizations followed this decision.
Antarctic and common minke whales separated into different species about 4.7 million years ago during a warm period in the early Pliocene. This warming disrupted the Antarctic Circumpolar Current and created areas where deep ocean water rose to the surface, splitting whale populations and leading to new species.
Two hybrids between Antarctic and common minke whales have been confirmed. Both were caught by Norwegian whaling ships in the northeastern North Atlantic. The first, an 8.25-meter (27.1-foot) female, was caught near western Spitsbergen on June 20, 2007. She was the offspring of an Antarctic minke mother and a common minke father. The second, a pregnant female caught near northwestern Spitsbergen on July 1, 2010, had a common minke mother and an Antarctic minke father. Her unborn calf was fathered by a North Atlantic common minke, showing that hybrids can sometimes mate with one of the original species.
Description
The Antarctic minke whale is one of the smallest baleen whales, with only the common minke and the pygmy right whale being smaller. The longest Antarctic minke whale recorded off Brazil was an 11.9-meter (39.0-foot) female caught in 1969 and an 11.27-meter (37.0-foot) male caught in 1975. The female was 4 feet longer than the second-longest female, and the male was 5 feet longer than the second-longest male. Off South Africa, the longest measured were a 10.66-meter (35.0-foot) female and a 9.75-meter (32.0-foot) male. The heaviest Antarctic minke whales recorded in the Antarctic were a 9-meter (29.5-foot) female weighing 10.4 metric tons (11.5 short tons) and an 8.4-meter (27.6-foot) male weighing 8.8 metric tons (9.7 short tons). At physical maturity, females average 8.9 meters (29.2 feet) and males average 8.6 meters (28.2 feet). At sexual maturity, females average 7.59 meters (24.9 feet) and males average 8.11 meters (26.6 feet). Calves are estimated to be 2.74 meters (9 feet) at birth. In a study by Konishi in 2008, the longest individuals were a female measuring 10.22 meters (33.5 feet) and a male measuring 9.63 meters (31.6 feet). The heaviest individuals were a female weighing 12.5 metric tons (28,000 pounds) and a male weighing 11.05 metric tons (24,400 pounds).
The Antarctic minke whale is similar in body shape to the common minke whale. It has a narrow, pointed, triangular snout with a low splash guard. Its prominent, upright, curved and pointed dorsal fin is located about two-thirds of the way along the back. About half of the individuals have a light gray flare or patch on the back half of the dorsal fin, similar to patterns seen in some dolphin species. The whale is dark gray on the back and clean white on the belly. The lower jaw extends beyond the upper jaw and is dark gray on both sides. Unlike the common and dwarf minke whales, the Antarctic minke lacks a light gray rostral saddle. All individuals have pale, thin blowhole streaks that trail from the blowhole slits, first curving left and then right, especially the right streak. These streaks are more visible and consistent on this species than on the common or dwarf minke. Most also have a variably colored ear streak behind the opening for the ear, which widens and becomes more diffuse toward the back. A light gray, double chevron or W-shaped pattern lies between the flippers, forming a light gray shoulder patch above the flippers. Like the common and dwarf minke, they have two light gray to whitish areas called the thorax and flank patches. The thorax patch runs diagonally from the armpit and forms a triangular shape on the chest, while the flank patch rises vertically and extends upward before sloping backward to merge with the white underside of the tail. A dark gray triangular area separates the thorax and flank patches, and a narrower dark gray area separates the thorax patch from the shoulder patch. Two light gray, forward-pointing chevrons on the tail extend from the dark gray area, creating a whitish blaze between them. The smooth, flat tail flukes are usually 2.6 to 2.73 meters (8.5 to 9.0 feet) wide, dark gray on top, and clean white (occasionally light gray or gray) on the bottom, with a thin, dark edge. Some small dark gray spots may be present on the body.
The Antarctic minke whale does not have the bright white, horizontal flipper band of the common minke or the white shoulder blaze and bright white flipper patch of the dwarf minke. Its narrow, pointed flippers, which are about one-sixth to one-eighth the body length, are usually light gray with a nearly white leading edge and a darker gray trailing edge or have a thin light gray or dark band separating the darker gray of the front third of the flipper from the lighter gray of the back two-thirds. Unlike the dwarf minke, the dark gray area between the eye and flipper does not extend to the throat’s ventral grooves to form a dark throat patch. Instead, there is an irregular line running from the eye level to the front of the flipper, merging with the light gray of the shoulder patch.
The longest baleen plates average 25 to 27 centimeters (9.8 to 10.6 inches) in length and 12.5 to 13.5 centimeters (4.9 to 5.3 inches) in width, with 155 to 415 pairs (average 273). These plates are two-toned, with a dark gray outer edge on the back plates and a white outer edge on the front plates, though some rows of dark plates may be present among the white plates. There is an uneven distribution, with fewer white plates on the left side (about 12% on average) than on the right (about 34% on average). The dark gray border covers about one-third of the plate’s width (ranging from one-seventh to over half), with the average width being greater on the left side than on the right. In contrast, dwarf minkes have smaller baleen plates (20 centimeters or 7.9 inches long), more white plates (over 54%, often 100%), and lack this uneven coloration. Dwarf minkes also have a narrow dark gray border (less than 6% of the plate’s width) when present. Antarctic minkes have an average of 42 to 44 thin, narrow ventral grooves (ranging from 32 to 70) that extend to about 48% of the body length—short of the umbilicus.
Distribution
Antarctic minke whales are found in many areas of the Southern Hemisphere. Some may travel near the equator into the Northern Hemisphere. In the western South Atlantic, they have been seen off Brazil between 0°53'N and 27°35'S (nearly year-round), Uruguay, central Patagonia in Argentina (November–December), and in the Strait of Magellan and Beagle Channel of southern Chile (February–March). In the eastern South Atlantic, they have been recorded in the Gulf of Guinea off Togo, Angola, Namibia (February), and Cape Province, South Africa. In the Indian and Pacific Oceans, they have been seen off Natal Province, South Africa, Réunion (July), Australia (July–August), New Zealand, New Caledonia (June), Ecuador (2°S, October), Peru (12°30'S, September–October), and the northern fjords of southern Chile. Vagrants have been reported in Suriname, where an 8.2 meters (26.9 feet) female was killed 45 km (28 mi) upstream the Coppename River in October 1963; the Gulf of Mexico, where a 7.7 meters (25.3 feet) female was found dead off Louisiana, USA, in February 2013; and off Jan Mayen (June) in the northeastern North Atlantic.
During the breeding season, Antarctic minke whales move into offshore waters. In spring (October–December), surveys from 1976 to 1987 found many minke whales off South Africa and Mozambique (20°–30°S, 30°–40°E), Western Australia (20°–30°S, 110°–120°E), the Gambier Islands of French Polynesia (20°–30°S, 130°–140°W), and the eastern South Pacific (10°–20°S, 110°–120°W). Later surveys, which separated Antarctic and dwarf minke whales, showed that most of these were Antarctic minke whales.
Antarctic minke whales are found around the Southern Ocean year-round, including the Bellingshausen, Scotia, Weddell, and Ross Seas. They are most common in the MacKenzie Bay–Prydz Bay area (60°–80°E, south of 66°S) and are often seen off Queen Maud Land (0°–20°E, 66°–70°S), the Davis Sea (80°–100°E, south of 66°S), the Ross Sea (160°E–140°W, south of 70°S), and the southern Weddell Sea (20°–40°W, south of 70°S). Like blue whales, they prefer areas with pack ice. In spring (October–November), they are found widely in pack ice zones near the edge of fast ice, between ice belts, and in leads and polynyas, even in heavy ice. Some whales have been trapped in ice and forced to overwinter in Antarctica, such as up to 120 "lesser rorquals" trapped in a small breathing hole with sixty killer whales and an Arnoux's beaked whale in Prince Gustav Channel, east of the Antarctic Peninsula and west of James Ross Island, in August 1955.
Two Antarctic minke whales marked with "Discovery tags" (26 cm stainless steel tubes with inscriptions and numbers) in the Southern Ocean during the austral summer (January) were found later off northeastern Brazil (6°–7°S, 34°W) during the austral winter (July and September). The first was tagged near Queen Maud Land (69°S 19°E) and the second southeast of the South Orkney Islands (62°S 35°W). Over twenty tagged whales showed large-scale movements around Antarctica, each moving more than 30 degrees of longitude. One moved at least 114 degrees of longitude from the Adélie Coast (66°S 141°E) to the Princess Ragnhild Coast (68°S 26°E). Another moved over 139 degrees of longitude from north of Cape Adare (68°S 172°E) to northwest of the Riiser-Larsen Peninsula (68°S 32°E). Both were tagged and recovered in January.
On 20 January 1972, a 49.5 cm (19.5 in) broken piece of a marlin’s bill (Makaira sp.) was found embedded in the rostrum of a minke whale caught in the Southern Ocean at 64°06′S 87°14′E, providing indirect evidence of migration to the warmer tropical or subtropical waters of the Indian Ocean.
Earlier estimates suggested there were several hundred thousand minke whales in the Southern Ocean. In 2012, the Scientific Committee of the International Whaling Commission estimated there were 515,000. The report noted this estimate might be slightly lower because some whales were outside surveyable ice edge boundaries.
Biology
Antarctic minke whales reach sexual maturity at 5 to 8 years for males and 7 to 9 years for females. Both genders become physically mature at about 18 to 20 years of age. After a pregnancy lasting about 10 months, a single calf measuring 2.73 meters (9.0 feet) is born. Twin and triplet births have been recorded but are uncommon. The calf is weaned after about six months of nursing, at a length of 4.6 meters (15 feet). Calves are born every 12.5 to 14 months on average. Peak calving occurs between May and June, while peak conception happens between August and September. Most Antarctic minke whales live less than 50 years, though one female was estimated to be 47–48 years old. The oldest Antarctic minke whale recorded in 1967/68, measured using earplugs, was 40 years old. A study by Konishi in 2008, which analyzed earwax, estimated the maximum lifespan of Antarctic minke whales to be 59 years for females and 63 years for males.
Antarctic minke whales primarily eat euphausiids, a type of small crustacean. In the Southern Ocean, over 90% of these whales feed on Antarctic krill (Euphausia superba). Another species, Euphausia crystallorophias, is also an important food source in some areas, such as the shallow waters of Prydz Bay. Rarely, they consume other prey, including calanoid copepods, the pelagic amphipod Themisto gaudichaudii, Antarctic sidestripes (Pleuragramma antarcticum), the crocodile icefish Cryodraco antarcticus, nototheniids, and myctophids. Many whales caught off South Africa had empty stomachs, but those with food mainly ate euphausiids, such as Thysanoessa gregaria and Euphausia recurva.
Antarctic minke whales are the primary prey of Type A killer whales in the Southern Ocean. Their remains have been found in the stomachs of killer whales caught by the Soviets. Japanese-caught whales often showed signs of attacks, including damaged flippers with tooth marks and scars on their bodies. Large groups of killer whales have been seen chasing, attacking, and killing Antarctic minke whales. Most attacks involve Type A killer whales. However, in January 2009, a group of ten Type B killer whales, which typically hunt Weddell seals by washing them off ice floes, were observed attacking and feeding on a juvenile Antarctic minke whale in Laubeuf Fjord, located between Adelaide Island and the Antarctic Peninsula.
Few studies have been published on the parasites and organisms that live on Antarctic minke whales. Many whales have orange-brown to yellowish patches of the diatom Cocconeis ceticola on their bodies, found in 35.7% of whales off South Africa and 67.5% in the Antarctic. One-fifth of whales caught by a Japanese expedition along the ice edge had cyamids, a type of whale lice. One species identified was Cyamus balaenopterae. Hundreds of these lice can be found on a single whale, with an average of 55 per individual. Most are located near the ventral grooves and around the umbilicus. A copepod named Pennella was found on only one whale. Cestodes, a type of parasitic worm, were commonly found in the intestines, with one example identified as Tetrabothrius affinis.
Behavior
Antarctic minke whales are more social than smaller minke whales, such as the common and dwarf minke whales. In the Antarctic, the average group size was about 2.4 whales (adjusted for observer bias), with about 25% of sightings showing single whales and 20% showing pairs. The largest group observed had 60 individuals. Off the coast of South Africa, the average group size was about 2 whales, with nearly 46% of sightings showing single whales and 31% showing pairs. The largest group there had 15 individuals. Off the coast of Brazil, most sightings showed single whales (32.6%) or pairs (31.5%), with the largest group having 17 individuals.
Like common minke whales, Antarctic minke whales show differences in where and when they are found based on sex, age, and reproductive status. Off South Africa, young whales are most common from April to May, while adult whales (mostly males) dominate from June onward. In August and September, adult males often join groups of mother whales and their calves. Off Brazil, many young whales (especially females) are seen in July and August, but by September, most whales are adults. By October and November, nearly all whales are adults. In Brazil, females outnumber males by about two to one, while in South Africa, males outnumber females by about two to one. Over a quarter of female whales off South Africa were lactating (producing milk for their young), but lactating females are rare in the Antarctic. However, a mother whale and calf were seen together in the Antarctic during the winter (August) in the Lazarev Sea. In the sub-Antarctic and Antarctic regions, young whales are often alone and are found farther from shore, while adult whales are usually in mixed groups. Adult males are more common in middle latitudes, while adult females are more common in the higher latitudes near pack ice. In the Ross Sea, two-thirds to three-quarters of the whales are pregnant females.
An immature Antarctic minke whale was briefly seen with four dwarf minke whales near the Great Barrier Reef in July 2000.
Unlike common minke whales, Antarctic minke whales often have a visible blow (a spray of water from their blowhole) that is easier to see in calm waters near pack ice. They have been observed spyhopping (raising their head vertically) to breathe through narrow openings in pack ice. In winter (July–August), they have even been seen breaking through sea ice to create breathing holes. When swimming quickly in open water, they can create large sprays similar to those made by Dall’s porpoises. When feeding, they often dive sideways into dense groups of prey, opening their mouths wide and expanding their throat pleats to take in water and prey. After several short dives, they make a longer dive lasting up to 14 minutes. At night (8 p.m. to 2 a.m.), they make shallow dives (less than 40 meters or 130 feet), while during the day (2 a.m. to 8 p.m.), they make deeper dives (over 100 meters or 330 feet). In a 2019 study, scientists tracked several whale species, including Antarctic minke whales, for four years to study how migration patterns change with size. Most whales swam at an average speed of 1.9 meters per second (6.8 km/h or 4.3 mph), but one Antarctic minke whale reached a top speed of 8.3 meters per second (30 km/h or 19 mph).
Antarctic minke whales make many sounds, including whistles, bell-like calls, clicks, screeches, grunts, downsweeps, and a sound called "bio-duck." Downsweeps are low-frequency calls that drop in pitch from about 130 to 60 Hz, peaking at 83 Hz. Each call lasts 0.2 seconds and is about 147 decibels loud at a distance of one meter. The "bio-duck" call, first noticed in the 1960s and named by submarine operators for its duck-like sound, consists of repeated pulse trains ranging from 50 to 200 Hz, peaking at 154 Hz. These calls are sometimes accompanied by higher-pitched sounds up to 1,000 Hz. They occur every 1.5 to 3 seconds and are about 140 decibels loud at one meter. For many years, the source of the "bio-duck" call was unknown, but it was linked to Antarctic minke whales in a 2014 study. The sound has been recorded in the Ross and Lazarev Seas, over Perth Canyon, off Western Australia (late June to early December), and in the King Haakon VII Sea (April to December). The sound is made near the surface before diving to feed, but its purpose is still unclear.
Whaling
The ship Antarctic, sent by whaling pioneer Svend Foyn and led by Henrik Johan Bull, successfully harpooned at least three minke whales in the Antarctic between December 1894 and January 1895. Two of the whales were saved and used for fresh meat (one whale produced only two barrels of blubber). In December 1923, members of the first modern whaling expedition to visit the Ross Sea saw "a number of spouts" after leaving the ice edge. They soon discovered that the whales were small minke whales. In the 1950s, the few minke whales caught by the British were taken more for curiosity than for practical use. Christopher Ash, a chemist who worked on the British factory ship Balaena during this time, described how the whales were small enough to be lifted by their tails using a 10-ton spring balance and weighed entirely. He explained that this process usually happened when no other whales were nearby and the deck was empty except for a group of sightseers. However, the crowd often scattered when the whale started to spin and swing from side to side. Like Bull before him, Ash noted that minke whale meat was "fine-textured" compared to other whales and, if cooked properly, was almost like beef.
Minke whales were primarily hunted for their high-quality meat, which sold for as much as two dollars per pound in 1977. After larger whales like blue, fin, and sei whales were overharvested, whaling nations turned their focus to minke whales, which were smaller but more numerous. Though the Soviets caught several hundred minke whales in the 1950s, a significant catch did not occur until 1971–72, when over 3,000 were taken, nearly all by a single Japanese expedition. To avoid repeating past mistakes, the International Whaling Commission set a quota of 5,000 for the 1972–73 season. Despite these limits, the quota was exceeded by 745 whales, and later quotas reached as high as 8,000.
During the commercial whaling era, from 1950–51 to 1986–87, 97,866 minke whales (mostly Antarctic minke whales) were caught in the Southern Ocean, mainly by the Japanese and Soviets. The highest number caught in a single season was 7,900 in 1976–77. Because of their small size, whalers used harpoon guns with smaller calibers and "cold harpoons" (harpoons without explosive shells). To preserve meat quality, no air was pumped into the carcasses when they were tied to the ship for towing. While some expeditions were specifically organized to hunt minke whales, such as the Jinyo Maru (1971–72), Chiyo Maru (1972–74), and Kyokusei Maru (1973–74), most whaling expeditions ignored minke whales during peak seasons (November–December and late February to early March) and only caught them near larger whale hunting grounds. Minke whale hunting areas were much farther south (south of 60°S) than those for fin and sei whales.
From 1987 to the present, Japan has sent a fleet consisting of one factory ship and several catcher/spotting vessels to the Southern Ocean to catch Antarctic minke whales under Article VIII of the International Whaling Commission (IWC), which allows the killing of whales for scientific research. The first research program, the Japanese Research Program in the Antarctic (JARPA), began in 1987–88, when 273 Antarctic minke whales were caught. The quota and catch numbers increased to 330 and 440, respectively. In 2005–06, the second program, JARPA II, began. In its first two years, Japan aimed to catch 850 Antarctic minke whales and 10 fin whales each season (2005–06 and 2006–07). The quota was met in the first season, but a fire limited the catch to 508 whales in the second. In 2007–08, environmental groups disrupted operations, and only 551 whales were caught.
Beginning in 1968, more minke whales were caught off Natal, South Africa, to replace the declining numbers of larger species like sei whales. Between 1968 and 1975, 1,113 minke whales (mostly Antarctic minke whales, with a few dwarf minke whales) were caught in the region, with a peak of 199 in 1971. The whales were caught by ships with 90 mm harpoon guns and brought to the whaling station in Durban (29°53′S 31°03′E) for processing. Gunners avoided catching minke whales early in the day because sharks often ate the carcasses, forcing whalers to tow them while chasing other whales, which slowed their progress. They also could not use asdic (a type of sonar) because it frightened the whales and made chasing them longer. The whaling season ran from February to September, with the highest catch in September.
In 1966, minke whales became the target of whaling operations off northeastern Brazil (6°–8°S) due to the decline of sei whales. Between 1949 and 1985, over 14,000 minke whales were caught, with a peak of 1,039 in 1975. The whales were caught by several ships, including the Koyo Maru 2 (1966–1971), Seiho Maru 2 (1971–1977), and Cabo Branco (1977–1985), and brought to the whaling station in Costinha, operated by the Companhia de Pesca Norte do Brasil (COPESBRA) since 1911. The whaling season lasted from June to December, with the highest catch in September or October.
An 8.2-meter (27-foot) male Antarctic minke whale, confirmed by genetic testing, was caught west of Jan Mayen (70°57′N 8°51′W) in the northeastern North Atlantic on June 30, 1996.
Other mortality
Other causes of death include becoming entangled in fishing gear and being struck by ships. Entanglement in fishing gear has been reported near Peru and Brazil, while ship strikes have been reported near South Australia. All the cases involved young whales, either calves or juveniles.
Conservation status
The Antarctic minke whale is currently listed as Near Threatened by the IUCN Red List. The IUCN reports that the number of these whales is "clearly in the hundreds of thousands."
This species is included in Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is placed on Appendix II because its conservation status is not good or because it would greatly benefit from international cooperation through specific agreements.
Additionally, the Antarctic minke whale is protected under the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region.