North Atlantic, North Pacific, and Southern Right Whales (marine mammals)

 

Right whales occur in temperate to subpolar latitudes of all of the world’s oceans. North Atlantic [(Etibalaena glacialis (Miiller, 1776)] right whales were the first target of commercial whaling and the first whale species to be seriously depleted, and today the two Northern Hemisphere species are the rarest large whales in the world. North Atlantic and North Pacific [(E.japonica (Lacepede. 1818)] right whales remain critically depleted even after more than six decades of international legal protection and may still be facing the threat of extinction. Right whale populations off the eastern United States, Argentina, South Africa, and Australia have been the focus of intensive long-term research and may be some of the most intensively studied large whales. Nevertheless, there are many areas where our knowledge is sadly lacking and where additional research is critically needed.

I. Systematics and Nomenclature

A. Common Names

Conventional wisdom holds that the common name “right whale” comes from English whalers, who designated this as the “right” (i.e., correct) whale to hunt because it occurred near shore, swam slowly enough to be caught irom a small boat propelled by sails or oars, floated when dead, and yielded large amounts of valuable oil and baleen. Alternatively, it may have derived from the sense of right whale meaning “true whale,” as later formally recognized in the Latin generic name Eubalaena. Other common names in English include black right whale and black whale.

B. Systematics

While Northern and Southern Hemisphere right whales have long been treated as two species, it was recommended in 1998 that all right whales should be considered as a single species, Balaena glacialis. In June 2000, the International Whaling Commission s scientific committee reviewed right whale taxonomy. Although morphological differences are nearly absent, the most recent genetic evidence demonstrates that right whales of the North Atlantic, North Pacific, and Southern Ocean possess fixed, unique genetic patterns indicating complete and long-established isolation. Genetic data also show that North Pacific and southern [E. austral is (Desmoulins. 1822)] right whales are more closely related to one another than either is to North Atlantic right whales, making the traditional combination of North Atlantic and North Pacific animals as “northern right whales” a systematics error. Based on the evidence, the committee recommended that the three populations be considered as separate species. They also recommended retention of the generic name Eubalaena, published by J. E. Gray (see the accompanying box) to separate right whales from bowhead whales (Balaena nvjsticetus), the only other living species included in the family Balaenidae. However, while there are no currently accepted genetic criteria for differentiation at the generic level, systematic classifications are scientific hypotheses, subject to revision after further study. The few authors who have looked critically at morphological or molecular differences between right whales and bowheads have concluded that there is little evidence supporting their separation at the generic level and that those differences which do exist are less than those between species of Balaenoptera. In addition, the known fossil species of Balaena cannot be shown as more closely allied with either right whales or bowheads.

II. Description

Right whales have an extremely robust body form, bordering on rotund, with the girth at times exceeding 60% of total bodv length. The body is mostly black, sometimes with irregular white ventral patches. Some individuals may have a mottled appearance. and calves may sometimes be lighter colored. There is no dorsal fin. The pectoral flippers are large, broad, and blunt, and the flukes are very broad (up of 40% of body length), black on both dorsal and ventral surfaces, deeply notched, and smoothly tapered to the tips. Calves are 4.5-6 m long at birth; typical adults are 13-16 m. North Pacific right whales attain larger maximum sizes than the other species, up to 18 m and over 100 metric tons.

The head is relatively large, comprising about one-quarter to one-third of the total body length. The upper jaw is somewhat arched, and the margin of the lower lip forms a veiy pronounced curve. There are 200-270 baleen plates on each side Are Whale-lice Parasites?

The most conspicuous external characteristics of right whales are the callosities on the head. These are irregular patches of thickened, keratinized tissue, which are inhabited by dense populations of specialized amphipod crustaceans, known as cyamids or “whale lice” (see accompanying box). At least three species of whale lice occur on right whales: Cyamis gracilis, C. ovalis, and C. erraticus. In southern right whales the callosities are also inhabited by barnacles, Tubicinella sp. The callosities occur at the tip of the snout (called the “bonnet” by whalers), on the lower lips and chin, above the eyes, and in front of and behind the blowholes. The callosities are congenital and not caused externally, as their beginnings are present in fetuses and neonates, but the pattern is not fully developed and colonized by cyamids until the whale is at least several months old. The callosity patterns are unique to individuals and are therefore extremely useful as a natural “tag,” which allows repeated identification of individuals by photographs (Fig. 1).

The closest relative of the right whale is the bowhead whale. Bowheads are somewhat longer and substantially stouter, have relatively larger heads (about 40% of body length) with a more arched appearance, have much longer baleen plates (up to 5.2 m long), and completely lack callosities.

III. Distribution and Abundance

Right whales are found in the middle latitudes of both the Northern and Southern Hemispheres, between approximately 20° and 60°S and N latitudes (Fig. 2). There are three geographically isolated populations currently recognized as separate species: in the North Atlantic, North Pacific, and Southern Ocean. The populations are kept separated by Arctic ice and warm equatorial waters so that there is no interchange between populations, and apparently has not been for millions of years.

A. North Atlantic Right Whales

The historical range of North Atlantic right whales apparently extended as far south as Florida and northwestern Africa and as far north as Labrador, southern Greenland, Iceland, and Norway. The traditional hypothesis has been that there were separate stocks with little interchange on the western and eastern sides of the basin; however, recent evidence is casting some doubt on that model. Analysis of some 19th century whaling specimens in European museums shows that they do not differ genetically from living western individuals, and there have been one or two right whales seen in the eastern North Atlantic in recent years that were known individuals from the western stock. It is possible that the structure of a right whale population is that a particular ocean basin is inhabited by a single breeding population without long-term genetic isolation of stocks, but where return to traditional habitats learned from the mother (matrilineal habitat fidelity) maintains shorter term separation between two or more subsets of the population.

The present range of western North Atlantic right whales, from Florida to Nova Scotia with very occasional occurrence beyond those limits, is much reduced from its historical extent. The best estimate of present abundance is about 300 animals. In the eastern North Atlantic, there have been only a handful of right whale sightings in the last few decades. It is not known whether these represent a small remnant eastern stock or whether some or all of them are individuals from the known western population.

Right whales are in the genus Eubalacna cind include three species. Individuals con be identified with varying success using callosity patterns on the head. Southern right whales (E. australis), pictured here, are represented by multiple stocks, and some of these stocks appear to be both healthy and increasing, in contrast to the much reduced abundance and distribution of the North Atlantic right whale.

Figure 1 Right whales are in the genus Eubalacna cind include three species. Individuals con be identified with varying success using callosity patterns on the head. Southern right whales (E. australis), pictured here, are represented by multiple stocks, and some of these stocks appear to be both healthy and increasing, in contrast to the much reduced abundance and distribution of the North Atlantic right whale.

Worldwide range of right whales (Eubalaena glacialis, E. japonica, and E. australis). Much of what is shown here is relatively speculative based on sparse historical records of whaling catches and the available recent sightings. Most recent data come from areas relatively nearshore, with few or no data for the pelagic areas between the known coastal habitats.

Figure 2 Worldwide range of right whales (Eubalaena glacialis, E. japonica, and E. australis). Much of what is shown here is relatively speculative based on sparse historical records of whaling catches and the available recent sightings. Most recent data come from areas relatively nearshore, with few or no data for the pelagic areas between the known coastal habitats.

B. North Pacific Right Whales

The historical range in the North Pacific was similarly much more extensive than today. Right whales occurred from Japan and northern Mexico north to the Sea of Okhotsk, Bering Sea, and Gulf of Alaska. Recent sightings are extremely rare, primarily in the Sea of Okhotsk and eastern Bering Sea. There are no reliable estimates of abundance, and there may be even fewer whales than in the North Atlantic. There are also insufficient genetic or resighting data to address whether there is support for the traditional separation into eastern and western stocks.

C. Southern Right Whales

Right whales are known from several areas of the Southern Ocean. Multiple stocks have been hypothesized, including Argentina/Brazil, South Africa, east Africa/Mozambique, western Australia, southeastern Australia, New Zealand, and Chile. Additional stocks have been hypothesized for the central Indian Ocean, the Campbell and Auckland Islands in the southwestern Pacific, and Tristan da Cunha in the central South Atlantic. There have also been suggestions of even finer stock structuring, e.g., between Argentina and Brazil in the western South Atlantic or between Namibia and South Africa in the eastern South Atlantic. Preliminary genetic analysis shows incomplete separation between eastern and western South Atlantic right whales. Further genetic studies should shed light on the degree of gene flow and stock separation in southern right whales and on the possible role of matrilineal habitat fidelity in structuring the population.

Right whale populations in Argentina, South Africa, and Australia are presently the largest and the best studied. The total abundance of those three stocks is currently estimated at about 7000 animals, and all three stocks appear to be healthy and increasing at 7-8% annually.

IV. Ecology

A. Prey

Right whales feed entirely on zooplankton, especially on large calanoid copepods (crustaceans approximately the size of a grain of rice). At times they also feed on smaller copepods, krill (larger shrimp-like crustaceans), pteropods (tiny planktonic snails), or the planktonic larval stages of barnacles and other crustaceans. The details of their diet likely differ between regions, e.g., it is likely that krill comprise a higher proportion of the diet in southern right whales. It is also likely that right whales can be somewhat opportunistic, feeding on any prey of a size that can be filtered efficiently by the baleen, which does not swim strongly enough to escape, and which is concentrated into sufficiently dense patches to trigger feeding behavior. For example, there have been recent observations of North Atlantic right whales in the Bay of Fundy feeding on aggregations of salps.

B. Habitat

Right whales migrate annually between high-latitude feeding grounds and low-latitude calving and breeding grounds. These are substantial differences in the locations where most research has been conducted between the Northern and the Southern Hemispheres; therefore, there is often a lack of directly comparable information for different populations.

1. Feeding Grounds Right whale feeding takes place in spring, summer, and fall in higher latitude feeding grounds, where ocean temperatures are cooler and overall biological productivity is much higher. The best known right whale feeding grounds are in the western North Atlantic. These habitats are in nearshore and shelf waters, where some combination of bottom topography, water column structure and stratification, and currents acts to physically aggregate zooplankton into extremely dense concentrations. The densest zooplankton concentrations measured in the North Atlantic were found by sampling near right whales. There are probably also offshore feeding grounds, in locations not yet known, based on historical whaling records and on the fact that some known whales are often missing from the known habitats for months or years at a time. There must also have been other feeding grounds in the past, when the range of North Atlantic right whales was much more extensive.

Feeding grounds for the other species of right whales are much more poorly known. In the North Pacific, based on historical whaling records and the few recent sightings, the principal feeding grounds were most likely in the Sea of Okhotsk, central and eastern Bering Sea, and Gulf of Alaska. All of these feeding areas are much more pelagic or offshore than in the well-studied North Atlantic habitats. In the Southern Ocean, right whale feeding grounds are also apparently mostly in offshore, pelagic regions. Southern right whale feeding grounds are likely to be found associated with areas of extremely high productivity; limited sighting data available show most whales in the regions between the subtropical and Antarctic convergences.

2. Calving Grounds Calving in right whales occurs during winter. Where the calving grounds are known, they are in shallow coastal regions or bays. The only known current calving ground in the western North Atlantic is in coastal waters near Georgia and northeastern Florida. It has been speculated that other coastal areas, including Delaware Bay and Cape Cod Bay, may have been calving grounds before the population was depleted by whaling. It has been noted, for example, that Cape Cod is similar topographically to Peninsula Valdes in Argentina and is located at about the same latitude. In the eastern North Atlantic, Cintra Bay in northwestern Africa is believed to have been a historical right whale calving ground. It is possible that areas near the Azores and Madeira, as well as the Bay of Biscay, were also calving grounds. In the North Pacific, no right whale calving grounds have ever been discovered. In the Southern Hemisphere, shallow coastal waters and bays in many areas are currently known to be southern right whale calving areas or hypothesized to have been calving grounds historically, including Argentina, Brazil, Falkland Islands, Tristan de Cunha, Namibia, South Africa, Mozambique, Kerguelen Island, Australia, New Zealand, Auckland Islands, and Chile.

3. Breeding Grounds Breeding or mating also occurs during the winter. Because of the 3-year female reproductive cycle, breeding can take place geographically distant from calving. In the western North Atlantic, the location of the majority of the population during the winter is not known, and adult males are nearly absent from the calving ground. Breeding must occur wherever the adult population spends the winter, but it is not known whether there are specific, distinct winter habitats or whether the whales are broadly dispersed across wide regions of the North Atlantic.

In southern right whales, at least some mating occurs in or near the calving grounds, although there may be small-scale segregation of breeding adults from females with calves. In Argentina, because females are observed infrequently in these breeding groups in the year prior to calving, it is possible either that the mating which actually leads to conception occurs in some other, unknown habitat or that receptive females only visit coastal waters for very brief periods.

4. Learning and Habitat Use Circumstantial evidence suggests that learning is an important component of habitat selection in right whales. Calves apparently learn the locations of feeding grounds by accompanying their mothers during the first year of life and then return to those same habitats for the rest of their lives. This pattern of matrilineal habitat fidelity seems to be common in migratory whale species; resighting and genetic data demonstrate that it is responsible for population structuring in North Atlantic humpback whales.

C. Predators

Potential predators of right whales include killer whales and large sharks. There have been a few direct observations of killer whale attacks on right whales; more common are records of right whales in the North Atlantic, South Atlantic, and North Pacific with scarring patterns on the flukes that appear to be tooth rakes or missing pieces of the flukes. Predators may be more likely to attack calves or juveniles than adults. Predation may have been one of the selective pressures leading to the evolution of right whales’ use of shallow coastal habitats for calving, particularly since at least white sharks are known to often attack their prey from below.

V. Behavior

A. Aerial Behaviors

Right whales are observed to frequently perform highly energetic behaviors at or above the surface of the water. These aerial behaviors include breaching (jumping partly or almost completely above the surface), lobtailing (violently slapping the surface with the flukes), and flippering (slapping the surface with a pectoral flipper). The functions of these behaviors are not known. They all produce very loud sounds, which may sometimes have a communicative and/or aggressive function. Right whales in Argentina and South Africa have been observed to lift their flukes above the surface, where the flukes act like a sail and allow the wind to push the whale horizontally This “tail-sailing” behavior has not been reported in other habitats.

B. Feeding Behavior

Right whales are “skimmers” (Fig. 3). They feed by swimming forward with the mouth agape. Water flows into the opening at the front, and out through the baleen, straining their prey from the water. Feeding can occur at or just below the surface, where it can be observed easily, or at depth. At times, right whales apparently feed very close to the bottom, because they are observed to surface at the end of an extended dive with mud on the head. Typical feeding dives last for 10-20 min.

C. Reproductive and Social Behavior

Courtship in right whales often involves aggregations of whales termed “surface-active groups.” These are usually centered around a single female and may involve large numbers of males; groups of more than 20 animals have been observed. Often the female is belly-up at the surface, while the males stroke her with their flippers or attempt to push her under. There is some evidence that the female initiates the interaction by vocalizing. In the North Atlantic. surface-active groups are observed in all seasons, even though calving is highly synchronous and restricted to winter. Therefore much of the observed activity does not lead to fertilization and may serve a social function. The female may simply use the interactions to assess male quality for later mating. The interactions between males in the group generally involve very little of the violence and aggressiveness seen in humpback whales. One theory is that right whales engage in sperm competition, where the volume of semen is important in displacing the sperm of other males mating with the same female. Right whale testes may be the largest of any animal, at 2 m long and 500 kg each.

A "skimming' North Atlantic right whale feeding on plankton near the surface.

Figure 3 A “skimming’ North Atlantic right whale feeding on plankton near the surface.

D. Sound Production

Right whale vocalizations are primarily low-frequency moans, groans, belches, and pulses. Most acoustic energy produced is below 500 Hz, with some sounds up to 1500-2000 Hz. The functions of these sounds are not well understood. Hypothesized functions include maintenance of contact between separated individuals, threats or other aggressive signals, and social signals, including their possible involvement in surface-active group behavior.

VI. Life History

A. Age at Maturity

Information on the age at maturity in right whales is not available from whaling data as it is for other whale species taken by 20th century industrial whaling. The information must be derived from photoidentification studies which track known individuals from birth. The youngest mature female in the western North Atlantic was 4 at maturity and 5 at first calving. From both North Atlantic and Southern Hemisphere data, the average age at first calving is closer to 9 or 10 years. Age at maturity is not yet known for males, as there is no external method for identifying paternity. Newer genetic studies may be better able to identify fathers of calves and begin to provide data for age of maturity in males.

B. Growth

Growth in right whales is relatively rapid from birth to weaning at about age 1, by which time the calf approximately doubles in body length to 9-11 m. Available data on growth after age 1 are not entirely consistent. For example, some studies indicate that growth also can be relatively rapid in year 2, by which time total length may reach 12-13 m, and thereafter is much slower. However, South African right whales apparently grow little between ages 1 and 4. Growth after age 1 is likely to be dependent on feeding success. The western North Atlantic female that matured at age 4 remained with her mother well into her second year, possibly growing much faster than the typical rate by nursing for a longer period. Right whales are believed to reach sexual maturity at body lengths of 13-16 m.

C. Life Span

There are very few data on the longevity of right whales. Aging baleen whales is an extremely difficult problem. Japanese attempts to use the wax plug found in the auditory canal from the North Pacific right whales taken for research in 1956-1968 were not successful. The oldest known right whale to date was in the North Atlantic. A mother-calf pair near Fort Lauderdale, Florida, was pursued and shot at by fishermen on March 24, 1935. The calf was killed, but the mother escaped. A photograph of her published in the New York Herald Tribune at the time was later matched to photographs taken in Cape Cod Bay (by pioneering right whale researcher William E. Schevill) in April 1959. She was also photographed in 1980, 1985, and 1992. On August 13, 1995 she was photographed offshore, with a large, gaping wound on the head apparently caused by a ship strike. It is unlikely she could have survived that injury. Assuming she was at least 10 years old in 1935, she would have been at least 70 years old in 1995. Recent research on bowhead whales suggests that they may live even longer.

D. Reproduction

The typical reproductive cycle in mature female right whales is 3 years between births. The gestation period is approximately 1 year, and weaning occurs at about 1 year of age. The female then takes a third year to replenish her energy stores, although it is possible for a female who has been especially successful at feeding to skip the resting year and calve after only a 2-year interval (one case observed in the North Atlantic, and at least one in Argentina). An alternative explanation for an observed 2-year interval is calf mortality soon after birth and subsequent avoidance by the mother of the high energetic demands of lactation; documented twice in Australia. This presumes that the mother-calf pair is sighted during the brief interval between birth and death of the calf. Otherwise what would be observed is an apparent 5-year interval, of which 25 were recorded in the North Atlantic between 1980 and 1998. Calving has been observed very rarely; in other instances, known females have been sighted in the calving ground both before and after the calf was born.

VII. Fossil Record

Five fossil species of Balaena have been described from deposits of late Miocene, Pliocene, or Pleistocene age (2-10 million years old) from Europe and North America: B. affinis, B. etrusca, B. montalionis, B. primlgenius, and B. prisca. The last of these is similar enough to modern bowheads (B. rmjs-ticetus) that it may, in fact, not be a separate species. There is then a long gap in the balaenid fossil record to Morenocetus parvus, the oldest known member of the family, found in early Miocene (23 million years old) deposits in South America.

VIII. Interactions with Humans

A. Whaling

North Atlantic right whales were the first whales to be harvested commercially by the Basques along the Atlantic coast of western Europe as early as the 11th century. The whales were killed primarily for oil, which was sold across Europe, as the technology of die time did not permit preservation and transportation of meat. As populations nearest shore were depleted, Basque whaling expanded to more distant waters, reaching eastern Canada by 1530. Basque whaling in Canada was centered in the Strait of Belle Isle between Labrador and Newfoundland and took 300-500 whales per year at its peak. Catches were declining by 1610-1620 and ended in 1713, by which time they had taken as many as 40,000 whales, including both right whales and bowheads.

Local shore-based right whaling in North America began soon after the establishment of permanent colonies during the early 17th century. Peak catches were in die early 18th century (e.g., 86 in Nantucket, Massachusetts in 1726; 111 in Long Island, New York in 1707), and right whales in western North Atlantic waters may have been effectively extinct as a basis for a commercial fishery by the middle of the 18th century. The familiar Yankee whaling industry soon developed as a high-seas fishery targeting sperm whales; however, the whalers continued to opportunistically take any right whales encountered. Yankee whaling (including ships from several European nations) spread to the South Atlantic by 1775, into the South Pacific in 1789, and into the North Pacific by 1820. The Japanese had also begun their own shore-based fishery, which took some coastal migrant right whales, in die late 16di century.

The traditional high-seas Yankee whale fishery finally ended in the early 20th century, when it was replaced by modern industrial whaling. Total right whale catches (although records are not complete) were at least 38,000 in the South Atlantic, 39,000 in the South Pacific, 1300 in the Indian Ocean, 15,000 in the North Pacific, and at least a few hundred in the North Atlantic. Some shore-based whaling in the eastern United States persisted into the 1920s, but it was minor, with only 8 taken in Long Island after 1900. In the North Atlantic, the last episode of intensive right whaling was in the late 19th and early 20th century off Norway, Iceland, and Scotland, and the last right whales taken were at Madeira: 1 in 1952 and 2 in 1967. All right whale populations worldwide were protected from commercial whaling in the 1930s by the first International Convention for the Regulation of Whaling. However, the Japanese took 23 North Pacific right whales in the 1940s and 13 more under special scientific research permits between 1956 and 1968, some illegal takes of right whales along the coast of Brazil were reported in the 1950s, there was a significant amount of illegal Soviet taking of right whales in the North Pacific and Southern Ocean into the 1960s, and it is possible that there has been illegal right whaling elsewhere in the world.

B. Ship Strikes

The most significant human-related source of mortality at present in western North Atlantic right whales is collision with large ships. Between 1970 and 1999, 16 right whales were known to have been killed by ships, and 2 others were last seen with serious and probably fatal injuries. There are probably additional mortalities that are never discovered because the carcasses are lost at sea. Ship collisions may be less of a mortality factor in other oceans, where right whales spend less time in nearshore habitats or where the level of industrial development is lower, although at least three probable ship-strike mortalities have been recorded in recent years off the Brazilian coast.

C. Entanglements

The second most important human-related mortality factor in western North Atlantic right whales is incidental capture in commercial fishing gear. The gear involved is fixed gear (set in one location rather than towed behind a vessel), including sink gill nets, drift nets, and a variety of pot and trap fisheries. Since 1970, three right whales are known to have been killed by entanglements and eight others were seriously injured but disappeared and probably died. It is not always known whether entanglements occur in actively fishing gear or in gear that has been lost, damaged, or moved by storms or vessels (often termed “ghost” gear). There are few data on entanglement mortalities in other populations.

Entanglement seems to be very common in right whales. Many entanglements involve the tail, where the leading edges of the flukes begin, and leave characteristic scars afterward. Over 60% of whales in the western North Atlantic carry such scars, and some individuals have been entangled two or three times. Entanglements are therefore often not lethal. They may be more dangerous in younger animals, who might grow into a relatively benign entanglement until it becomes life-threatening.

D. Climate Change

Right whales are feeding specialists, with a relatively narrow range of acceptable prey species and requiring prey to be concentrated in exceptionally high densities. The development of right whale feeding grounds is closely linked to physical phenomena such as water structure, currents, and temperature. This may make right whales more sensitive than other species to impacts from global climate change. Any possible impacts may be increased because of matrilineal fidelity to their feeding grounds, and possibly a relatively low ability to locate new feeding grounds when conditions change. For example, right whales have never reoccupied the habitat in the Strait of Belle Isle where Basque whaling killed many thousands.

E. Other Human Impacts

There are a number of other potential human impacts on right whales:

1. Habitat loss due to high levels of human activity is mentioned frequently as a possible impact. Right whales no longer occur in Delaware Bay, eastern United States; Table Bay, South Africa; Wellington Harbor, New Zealand; or Derwent River, Tasmania. However, a plausible alternative explanation is that they were extirpated by whaling and have never reoccupied the habitat due to matrilineal habitat fidelity.

2. Pollution is another potential impact that is mentioned frequently but where evidence is sparse. Oil spills may be a bigger threat to right whales than to other baleen whales because their very fine baleen might be fouled more easily. Blubber samples show a presence of toxic contaminants, but at lower levels than in cetaceans that feed at higher trophic levels. A recent concern is that some contaminants may act as hormone mimics, affecting reproduction, or as immune system suppressants.

3. Man-made noise may have the potential for interfering with acoustic communication, particularly since the major noise source, shipping, is also concentrated in the lower frequencies.

4. Effects of intensive commercial fisheries may alter ecosystem structure, increasing the abundance of other species that feed on zooplanlcton, particularly small fishes with lower economic value than the larger species harvested by fisheries.

5. The long-term effects of extreme population depletion by whaling might include reduced genetic diversity and associated health and reproductive problems.

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