Little killer whale
|Little killer whale|
Little killer whale
|Scientific name of the genus|
|Reinhardt , 1862|
|Scientific name of the species|
|( Owen , 1846)|
The little killer whale ( Pseudorca crassidens ), also known as loggerhead or black killer whale , is a species of dolphins (Delphinidae) and the only recent representative of the genus Pseudorca . It is similar to the Orca in shape and proportions, but is monochrome black and with a maximum length of about six meters, significantly smaller. Small killer whales form schoolsof an average of ten to fifty animals, although they also socialize with other dolphins and mostly stay away from the coast. They are native to all oceans of temperate, subtropical and tropical latitudes, but are found, especially in warmer seasons, as far as the temperate to subpolar zone south of the southern tip of South America, off northern Europe and off Canada.
Like other dolphins, the killer whale is an active hunter and feeds mainly on larger fish and cephalopods , but can also attack smaller dolphins or large whales in isolated cases. Compared to the great killer whale ( Orcinus orca ) and some other dolphin species, little research has been done on it and sightings are comparatively rare. Strandings occur, sometimes as mass strandings with several hundred animals, but are less frequent than with the more well-known species.
The killer whale is, apart from the killer whale, one of the largest species among dolphins. The males of the killer whale reach body lengths of up to 6.10 meters and a maximum weight of 2200 kilograms, the females remain significantly smaller with a maximum of 5.10 meters and a maximum weight of 1200 kilograms. The newborn young animals are 1.5 to 2.0 meters in length and weigh around 80 kilograms. The body of the animals is colored completely dark gray to black on the back and the flanks as well as on the belly and the dorsal fins, the flippers and the caudal fin ( fluke ) also correspond to the body color. In good lighting conditions, it can be seen that the back from the dorsal fin to the back is darker in color like a cloak than before, the darkest pigmentation is in the area of the attachment of the fluke. There is often a grayish to almost white anchor-shaped spot between the pectoral fins, which in some individuals can begin at the throat and end in a line that extends to the genitals . In some cases the animals also have a light gray spot on the sides of the head. The typical dark color is already present in the young animals and could also be detected prenatally in an embryo about 70 centimeters long . In contrast to the closely related round-headed dolphin ( Grampus griseus ), scars from internal and external interactions form new pigments and thus turn black again; however, the body may have local star-shaped scars from healed cigar shark ( Isistius ) bites .
The body of the whale is relatively slim and the head is only short in relation to the total length. The forehead area ( melon ) is long and slightly arched; there is no separate beak. In the adult males, the melon is more prominent than in the females and juvenile whales. The area around the blowhole is slightly arched. The sickle-shaped dorsal fin is roughly in the middle of the body ; the relatively short pectoral fins (flippers) start far in front of the body and have a species-typical shape with an S-shaped front edge and a pointed, rounded fin tip. The caudal fin (fluke) is also short; the indentation in the middle is not very pronounced.
Features of the skull and skeleton
The killer whale skull is sturdy with a short and wide snout region. This is at least 1.5 times as long as it is wide and widens with the age of the animals. The total length of the skull of an adult animal is just over 50 centimeters. The whale has very strong, conical and curved teeth . There are seven to eleven teeth per half of the jaw in the upper jaw and eight to twelve teeth in the lower jaw, although in many animals the number of teeth in the right lower and upper jaw does not correspond to that in the left (bilateral asymmetry). The uniform or homodontic dentition of this species, in which there are no different types of teeth as in other mammals, is typical of the entire suborder of the toothed whale and represents an adaptation to their preferred food from difficult to fixate, streamlined and smooth prey such as fish and cephalopods .
The skull of the killer whale can be distinguished from that of the killer whale by the proportions of the bones to one another: In the killer whale, the width of the intermaxillary bone (premaxillary) directly in front of the antorbital notches, i.e. the notches in front of the eyes, is more than 50% of the total width of the Facial skull, less than 50% in the little killer whale. In addition, the side edge of the intermaxillary bones is more S-shaped when viewed from above and wider in the front area. The tympanic cavities reach a length of 47.7 to 50.5 millimeters, they have an atrophied keel and are not laterally flattened.
The spine consists of 7 cervical vertebrae , 9 to 11 thoracic vertebrae , 9 to 13 lumbar vertebrae and 16 to 26 caudal vertebrae , the total number of vertebrae being 47 to 52. In numerous animals, the first four to seven caudal vertebrae in particular are in different numbers with one another fused, the number of fused vertebrae likely to increase with age. The chest consists of 9 to 12, mostly 10 pairs of ribs , 6 of which each have two origins (bicipital). The number of ribs on each side of the body can be different. Four pairs of ribs are fused directly to the sternum , six more are connected to it by cartilage . The 11th and 12th pairs of ribs, if any, are not connected to the breastbone and accordingly end freely. The breastbone itself consists of four parts that grow together with age. The number of finger bones in the flippers can vary widely, usually the animals have zero to one bone on the first, four to eight bones on the second, four to six bones on the third, one to three bones on the fourth and zero to two bones on the fifth Finger. As with all whales, the fingers are connected to a fin (flipper) via the surrounding tissue.
Like other whales, the killer whale has the typical chromosome set of 2n = 44 chromosomes for this group of animals . The karyotypical killer whale is estimated to be more stable than the killer whale. Hybridizations with bottlenose dolphins have occurred repeatedly in captivity because the genomes of these two species are compatible.
The killer whale is an offshore species that can be found in the temperate to tropical areas of all oceans . Sightings away from the coast are relatively rare, and strandings only occur occasionally. The whale has been observed frequently in the Atlantic off the North American coast and in the Caribbean . It also occurs regularly in the Pacific and Indian Oceans . The distribution area also includes individual demarcated marine regions such as the Mediterranean Sea , the Gulf of Mexico , the Gulf of California , the Red Sea and the Arabian Sea and the Sea of Japan . In the area of tropical islands, especially around Hawaii, the animals are also found near the coast. The animals probably make seasonal migrations and come to shallower waters near the coast, especially in winter.
The main area of distribution is between the 40th north and 40th south latitude. The animals have been detected in water areas with a temperature between 8 and 31 ° Celsius, whereby they prefer higher water temperatures. The most southerly distribution of the animals so far is documented by a group of killer whales from the region east of the southernmost point of the South American continent at Cape Horn , Chile . This sighting also showed that the animals can live at least temporarily in cold water areas of up to 8 ° Celsius. When 22 small killer whales were mass stranded on the east coast of the Falkland Islands in 2013, the species was also detected for the first time in this region.
The European records of the species mostly come from sightings of individual groups of whales and from reports of stranding. They were made on the coasts of Great Britain , Spain , the Netherlands and the German and Danish North Sea coasts . There are also rare sightings in the Baltic Sea and the Mediterranean , especially from southern Spain and Italy . The northernmost records in North America come from Canada, where in May 1987 an individual stranded on Denman Island , British Columbia .
Way of life
The killer whale is a species of whale that prefers the deep areas of the oceans, i.e. the pelagic , as a habitat. Accordingly, these whales can mainly be observed in the high seas, but also near islands and coasts that are surrounded by deep water. Due to the distance from the coast and the life in the high seas, the way of life of the killer whales has not been adequately researched. Most of the information about the species comes from studies of stranded animals, animals living in captivity, and sightings primarily near the coast, such as around Hawaii and other islands.
The animals are active during the day and night, with likely their maximum activity during the day. The whales live in schools with an average size of 5 to 25 individuals, although larger groups of over 100 to 400 animals have occasionally been observed. The groups sometimes swim far apart at speeds of 5 to 20 kilometers per hour, and a school can stretch over a length of up to 20 kilometers. The animals regularly jump completely out of the water. Within the schools, killer whales have strong social ties between the individual animals, with the individuals sometimes staying together for years. These smaller, more stable groups are mixed in age and sex, and there does not seem to be any apparent gender or age segregation in this species. Larger groups are often amalgamations of several small schools, which usually separate again after a while. The largest documented stranded group of whales to date consisted of 835 individuals in Mar del Plata ( Argentina ) in 1946.
It happens that schools join forces with other whales, mainly schools of bottlenose dolphins ( Tursiops truncatus ) and rough-toothed dolphins ( Steno bredanensis ), and form hunting communities. Above all, the relationship with the bottlenose dolphins can last for several years, as was found in long-term studies around New Zealand. The groups consist of animals of different ages, whose social structure is very pronounced. Long-term relationships within schools of up to 15 years have been demonstrated in the areas around Hawaii, and mass stranding of these animals is attributed to these close individual ties. Little is known about the diving behavior of this species; one tagged animal dived for up to 12 minutes and at depths of over 230 meters.
The killer whale has a varied repertoire of tones for intra-species communication as well as for sonar orientation and for catching prey. Above all, they use drawn out calls at a frequency of 28 kHz, which last around 60 to 75 milliseconds and have a wave-like frequency pattern similar to that of the porpoise. There are also longer click sequences, single or double clicks with a frequency of around 100 kHz and short whistles with a frequency of around 8 kHz. Using underwater sonograms, it was estimated that the hearing range of the animals ranges from 2 to 115 kHz with a hearing optimum between 32 and 70 kHz.
Like other dolphins, the killer whale feeds primarily on various fish and cephalopods. The composition of the food can vary greatly from region to region due to the available prey. It is assumed that the animals ingest about 4.7 to 5% of their weight in food daily, the calculation being based on animals in captivity. Hunting and feeding takes place regardless of the time of day, both during the day and at night; On the basis of stomach analyzes of stranded animals, a higher amount of food was given in winter than in the other seasons. The animals hunt together in schools and share the prey among themselves.
Among the prey are different among other pelagic squid and squid as Martialia hyadesi , Ilex argentinus , Berryteuthis magister , Gonatopsis borealis and Ommastrephes bartramii , further various fish such as sea salmon ( Oncorhynchus ), bonito ( Katsuwonus pelamis ), Large dolphinfish ( Coryphaena hippurus ) and other mackerel , moonfish ( Mene maculata ), Japanese sea bass ( Lateolabrax ), tuna ( Thunnus ) and sailfish ( Istiophorus platypterus ). Some of the prey, especially the tuna and sailfish, are quite large, and especially in the region around Japan the killer whale is known for eating tuna off the fishing lines. In other regions as well, such as around Hawaii and the Gulf of Mexico and the Indian Ocean, killer whales are one of the few species of toothed whales that occasionally steal fish from both commercial and recreational fishermen.
In addition, killer whales have been observed to attack smaller and young dolphins and feed on them. So far, this behavior has only been observed to a limited extent in the area of the tuna fishing zones in the Pacific, in which injured dolphins were freed from the lines and released. It is therefore only attributed to isolated populations with a certain adaptation to this additional food source. In rare cases, killer whales have also been observed to attack humpback whales ( Megaptera novaeangliae ) in schools and sperm whales ( Physeter macrocephalus ) in the Galápagos region .
Reproduction and development
Information and data on the development of the animals come almost exclusively from examinations of stranded individuals and often relate to dental examinations in order to determine the age of the stranded animals on the basis of the enamel layers. There is correspondingly different information about the age of sexual maturity and other age-related data. It is assumed that both sexes reach sexual maturity between the ages of 8 and 14, although it is assumed that the males are only able to mate later. For the marine areas off Japan it is assumed that the females reach sexual maturity with a length of 3.40 to 3.80 meters and thus at an age of 8 to 11 years; in the case of males, however, sexual maturity should only occur when they are more than 4.20 meters in length and around 18 years of age. In contrast, there are estimates that the males should be sexually mature by the age of 8 to 14. In contrast to the females, in whom sexual maturity goes hand in hand with the first ovulation , in the males this can only be determined with difficulty and indirectly, for example via the size and weight of the testicles .
The ovulation of the females will probably once a year, in which it takes place spontaneously and has no fixed periodicity. Only one egg is released per ovulation. The mating season is accordingly all year round, but regionally there may be an environmental periodicity. In the waters around Japan, for example, most pairings take place between December and January. The number of pregnant females within the population is estimated to be around 14.5%. The calving interval, i.e. the distance between two births of individual females, is given as around 7 years, and calving can take place all year round, with a peak in late winter. With the age of the females, the interval between calvings increases, and it is believed that females over 45 years of age will no longer have young. This was confirmed, among other things, by examining the ovaries of stranded whales from Japan and South Africa.
The gestation period is about a year and the females only give birth to one young at a time. In a 1997 documentation off the coast of Morocco , the birth of a killer whale could be observed. This took place in a group of killer whales that had approached a boat, and the mother was in the middle of this group when the young was born. The birth was recognizable by a spreading blood stain and a piece of placenta that was aborted. Immediately after birth, the group's whales lifted the newborn baby together above the surface of the water to allow breathing . Then it was lowered back into the water to swim with the group.
The young animal is about 1.50 to 2.0 meters long at birth. The mother's breastfeeding period is likely to be around 18 to 24 months thereafter. The maximum lifespan is assumed to be 57 years for the males and 62 years for the females. The generation duration is estimated to be 25 years.
Predators and parasites
Little information is available about predators of the little killer whale, but it is believed that individual animals are preyed on by large sharks or whales such as the killer whale. Attacks by large sharks are documented via typical scars from shark bites on living individuals. An attack by a school of killer whales on a mixed group of killer whales and porpoises near New Zealand was reported in 2010. The small killer whales were attacked from below in the manner typical for large killer whales and thrown out of the water. At least one killer whale calf was killed and eaten in the attack. Merging with other species is likely a predator avoidance strategy, with different species responding differently to potential attackers.
In addition, the whales, like others, are attacked by cigar sharks ( Isistius ), which with the help of their special teeth are able to tear pieces out of the whale's skin and eat them. Accordingly, the body of the whale can be locally littered with fresh wounds and star-shaped scars from the healed bites.
Parasites have been documented by stomach and intestinal examinations of stranded animals. During stranding in Brazil, for example, a high rate of infestation of the animals with roundworms of the species Anisakis simplex , Anisakis typica , Stenurus glocicephalus and Stenurus auditivus as well as scraper worms of the species Bolbosoma capitatum was found. The density of scratchworms was up to 600 individuals per meter of intestine length. In addition, unidentified tapeworms of the Tetrabothriidae family were found. Bolbosoma capitatum and Anisakis simplex were also detected earlier even at little killer whales, as well as numerous other whales, associated with the documentation of the flukes Nasitrema attenuata , Nasitrema globicephalae and Orthosplanchnus elongatus . As ectoparasites on the body of animals could Whale louse ( Syncyamus pseudorcae , Isocyamus delphini ), barnacles as Xenubalanus globicipitus and the barnacles belonging Conchoderma auritum be determined.
Only sporadic information is available about infectious diseases; acute pneumonia has been demonstrated in captive animals .
Taxonomy History and Fossil History
The first description of the little killer whale comes from 1846 based on a fossil recovered from a peat bog in Lincolnshire in 1843 by the zoologist and paleontologist Richard Owen , who recognized the skeleton of a whale in the remains, which he believed to be a possibly extinct species of the Delphinidae . He described the remains as subfossil, i.e. conserved in recent times, and dated the find to the middle Pleistocene with an age of about 126,000 years. He named the type Phocaena crassidens , thus placing it in the relationship of the porpoises . In 1846, John Edward Gray , in his description of the whales in The Zoology of the Voyage of HMS Erebus and Terror , a travel description of the Antarctic expedition by James Clark Ross from 1839 to 1843, assigned the species directly to the genus Orca (today Orcinus ) as Orca crassidens . The species was first found alive by Johannes T. Reinhardt , who examined a group of whales stranded in the Kiel Bay in 1861 and viewed them as a new genus closely related to the killer whales ( Orcinus orca ) , which he named Pseudorca in 1862 and which he included in the Owen classified the remains as Pseudorca crassidens together with the living specimens he describes . In 1864, William Henry Flower described Orca meridionalis, a species of killer whale from Tasmania that was new to him , which he referred to Pseudorca the following year and which was later synonymous . Other species descriptions that are now considered synonyms are Orca destructor Cope, 1866 , Pseudorca grayi Burmeister, 1869 and Pseudorca mediterranea Giglioli, 1882 .
In 1924, the Japanese vertebrate paleontologist Hikoshichiro Matsumoto described the fossil species Pseudorca yokoyamai as the only fossil representative of the genus so far, based on two fossil teeth from Japan . It was the Calabrium , a partial period of the Lower Pleistocene ago from 1.806 to 0.781 million years ago, dated.
In fact, the killer whale has long been considered to be closely related to the killer whale and placed with it in a subfamily orcinae within the toothed whale and dolphin. Genetic studies show that the small killer whale ( Pseudorca crassidens ) is more closely related to the pilot whale than to the great killer whale ( Orcinus orca ).
Phylogenetic systematics of the Delphinidae according to Horreo 2018
According to current studies, they are probably the sister species of a taxon from the two known species of the pilot whale ( Globicephala ) as well as the broad-billed dolphin ( Peponocephala electra ) and the dwarf pilot whale ( Feresa attenuata ). Together with the round-headed dolphin ( Grampus griseus ), these species form the subfamily Globicephalinae within the dolphins and are compared to the two species of the genus Orcaella .
William Henry Flower proposed as early as 1888 to distinguish a northern from a southern form and in 1945 Paules Edward Pieris Deraniyagala separated Pseudorca crassidens meridionalis as an independent subspecies, but without specific naming of characteristics on the basis of which the two subspecies could be separated from one another. This description is accordingly generally ignored and until today the species is regarded as monotypical without subspecies.
However, through genetic tests isolated populations and different haplotypes could be identified in different marine areas, there are also morphological differences, especially in the skull structure between individuals from Australia, Scotland, the waters around Hawaii and South Africa. In the case of the genetic diversity of the killer whales in the China Sea , the genetic differences in the haplotypes were so great, according to the authors, that the question was raised as to whether the species could be different. In the area around Hawaii it has been documented that there are genetic differences between the animals living near the coast and those of the open Pacific.
The killer whale is also known as the false killer whale or the false killer whale , in the English-speaking world it is called the false killer whale . Like the scientific generic name Pseudorca , this naming refers to the external similarity to the great killer whale ( Orcinus orca ), which is also known as the killer whale or orca. The scientific species name "crassidens" refers to the shape of the teeth ("crassus" = "thick" and "dens" = teeth).
Status and threat
The killer whale is a top predator and is generally considered to be rather rare, even in the regions with the highest population densities. The density is generally higher in the lower latitudes around the equator ; in the North Pacific, the density decreases massively north of about 15 ° north latitude. There are population estimates for a number of areas, some of which are quite out of date, and the estimates for larger areas may include more than one population . The only area that has both current population estimates and a good idea of the population structure is in Hawaiian waters. There are three established populations there, with partially overlapping territories. The main island population numbers between 150 and 200 individuals and uses an area around the main Hawaiian islands that is up to 120 kilometers from the coast. The population of the northwestern Hawaiian Islands is about 550 individuals. The pelagic population lives at least 1,700 kilometers from Hawaii and consists of around 1,550 individuals within the economic zone of the Hawaiian Islands. The total of estimates available for the total number of animals worldwide is about 60,000 animals, with the two largest estimates, which make up about 94% of the total, are more than 25 years old. Abundance estimates are not available for a substantial portion of the species' range, and therefore the overall abundance is likely much higher than these 60,000 animals. However, due to the low density of these whales, estimates are imprecise and trends cannot be assessed in most areas.
The International Union for Conservation of Nature classifies the killer whale as a type of the warning list ( near threatened ), whereby a classification close to the vulnerable level is given before the current data situation . The main threats to stocks are identified as accidental killing as bycatch in fisheries and, in some areas, targeted hunting or killing of the animals. Due to the comparatively long generation of around 25 years and the associated slow population development, even comparatively low killing rates in the killer whale can lead to a negative population development. The little whale falls like all small cetaceans not covered by the protective provisions of the International Whaling Commission (IWC) in cites it is listed in CITES Appendix II. The Hawaiian population is classified as endangered under the US Endangered Species Act.
In addition to direct fishing and the killing of the animals as fishing competitors, there are other threats to the animals from environmental pollution and pollution. The killer whale is one of the species in which the ingestion of discarded plastic has been noted. In some tissues collected from stranded animals, high levels of poison and heavy metals could be documented. Very high silver concentrations were recorded in the organs of whales in stranded animals in South America, and in another study of stranded whales in Chile, very high concentrations of selenium and mercury were found in tissue samples. In Hawaiian waters, 84% of the whales sampled showed polychlorinated biphenyls (PCBs) in concentrations well in excess of proposed health thresholds, suggesting that there may be immunosuppression or reproductive effects in the affected populations. Also dichlorodiphenyldichloroethylene , a degradation product of the plant protection agent dichlorodiphenyltrichloroethane (DDT), was partly detected in a high concentration.
Interactions with humans
Fishing and by-catch
In Europe there has never been any specific economic use of the killer whale, but it is occasionally caught as bycatch in tuna and swordfish . In Japan, the animals are occasionally used as a source of food, with animals mostly appearing near the beach being driven to the shore and harpooned and killed there. They were also caught in St. Vincent and Taiwan and used as a source of food and oil. Given the high numbers of animals trapped in some of the areas where this has been studied, killing these whales could have had a significant impact on the local population.
In all areas where the killer whale habitats overlap with the fishing areas of large-scale commercial fisheries, injuries and kills occur as bycatch by the fishing industry. This happens regardless of whether it is trawling, longline or hook fishing. In well-studied Hawaiian waters, the number of animals killed and injured accidentally killed or seriously injured in longline fishing is likely to be greater than the population can sustainably survive, and it is believed that the same is true of almost all other fishing areas . In addition, there is an indirect influence on populations and their food supply in areas in which a high proportion of fish populations is commercially interesting and used.
This species is not very popular with commercial fishermen because it steals tuna from the lines that have already been caught. This also increases the risk for the animals to be caught themselves. On the Japanese island of Iki there was a concerted action by fishermen to exterminate the species in the region. Between 1965 and 1990, nine hundred killer whales were killed in the vicinity of Iki .
Whale watching and keeping
In Hawaii and in other regions such as New Zealand or Morocco, the animals are regularly encountered by commercial whale or dolphin watching vessels. Small killer whales have also been and are kept captive for scientific and entertainment purposes in a number of aquariums around the world, including Japan, the United States, the Netherlands, Hong Kong and Australia. They have been successfully bred in captivity at various locations, and in some cases viable hybrids with bottlenose dolphins have also emerged in captivity .
As with other whales, the killer whale is stranded more or less regularly , sometimes affecting entire schools or larger groups. However, they are comparatively rare compared to the more well-known species of dolphins.
The largest documented stranding of animals of this type occurred in Mar del Plata ( Argentina ) in 1946 and consisted of 835 individuals. In contrast to other dolphins, but similar to pilot whales, killer whales tend to get stranded in large groups, which leads to comparatively high mortality rates. These can also occur in temperate waters outside of its central distribution area, such as the mass beachings in Great Britain or Denmark. The reasons for the stranding are largely unknown. It is assumed that they happen due to misorientation of individual animals, which the entire group then follows. Environmental conditions such as water pollution and noise emissions, diseases or poisoning of the animals and other factors probably also play a role.
The mass stranding of 114 killer whales on July 30, 1986 in Flinders Bay , Western Australia , was observed by many people internationally and received a great deal of media coverage. The newly created Australian Department of Conservation and Land Management (CALM) saved 96 animals and established an informal network for whale strandings. The stranding of 120 animals in Geographe Bay on June 2, 2005 in Western Australia, the fourth in that bay, was caused by a storm that prevented the animals from seeing the shoreline. Here, too, a rescue operation was started, in which 1500 volunteers were organized by CALM.
Numerous other strandings have been and are being documented, and they occur in almost all regions of the distribution area. There have been at least seven strandings in New Zealand since 2005 and mass strandings have also been reported from South Africa and Florida in recent years.
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