Crabeater
| Crabeater | ||||||||||||
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Crabeater |
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| Systematics | ||||||||||||
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| Scientific name of the genus | ||||||||||||
| Lobodon | ||||||||||||
| JE Gray , 1844 | ||||||||||||
| Scientific name of the species | ||||||||||||
| Lobodon carcinophaga | ||||||||||||
| ( Hombron & Jacquinot , 1842) |
The Crabeater ( Lobodon carcinophaga ) is in south polar waters common seal , which is named after their unusual diet.
features
Crabeater have a slender, streamlined shape with a clearly visible neck. This is how they can be distinguished from many other Antarctic seal species from a distance.
The color of the crabeater changes with the seasons. In the summer coat (January / February) it is colored silver-gray. In the following months, the color fades more and more to a creamy yellow shade. Brown areas of fur extend over the back, flanks and fins. The exact pattern and coloration is different for each individual. The fins are always the darkest parts of the body. As a rule, however, males are slightly lighter than females; but since this is only a statistical evaluation, it cannot be used to differentiate between the sexes.
This seal is about 220 to 245 cm long and relatively light at 170 to 230 kg in weight. Males are on average 5 cm smaller and 8 kg lighter than females. The largest crabeater ever recorded was a female 277 cm in length.
The crabeater's teeth are adapted to the diet and differ from all other seal bites. The teeth have tubular recesses on their surface. When the seal closes its mouth, the teeth of the upper and lower jaw fit exactly between each other and water can only penetrate through the recesses. The largest gap between the teeth is then 2.6 mm. These teeth serve as a filter for planktonic food (see below).
Crabeater have sharp claws on the front fins, while the claws of the rear fins are reduced to horny stumps.
distribution
The crabeater is an Antarctic seal. In summer it lives in the waters of the Southern Ocean and colonizes the edge of the pack ice. In winter the crabeater wanders far and wide and then reaches the coasts of Patagonia and various sub-Antarctic islands. Crab eaters seen further north are mainly juveniles that have been driven away by the currents. Such wanderers have been seen on the coasts of Australia , New Zealand , South Africa and South America . The northernmost place where a crabeater has ever been seen is near Rio de Janeiro .
Way of life
nutrition
The crabeater is the only seal that has adapted to the diet of plankton animals . The Antarctic krill ( Euphausia superba ) is by far the most important prey. It makes up more than 90 percent of all food. The crabeater eats the krill by taking in water with its mouth open and then pressing it out again through the filter system of its teeth. The krill gets stuck in the teeth and is swallowed. A fish can also be captured in the same way, but the maximum size of the fish caught by the crabeater is 10 cm.
As well as krill of the genus Euphausia, the Antarctic silverfish , crocodile ice fish , squid , amphipods and hover shrimp have been identified as preyed by crab eaters .
The crabeater does not have to dive very deep to find the readily available food; his dives therefore usually lead him to depths below 10 m, rarely up to 50 m. However, a maximum diving depth of 528 m has also been proven. Typically, crab eaters stay underwater for three to six minutes, followed by a half to one minute stay on the surface. The maximum measured diving time was eleven minutes. On average, crab eaters stay in the water for sixteen hours before venturing out onto the ice to rest.
behavior
Sexually mature crab eaters live solitary or in small groups. These groups are only found temporarily without any ties between the members. When resting, the groups consist of two to five seals, in the water you can find up to 30 crab eaters swimming next to each other. In exceptional cases, group sizes can reach fifty (resting) or five hundred (swimming).
A special case are immature seal pups, which gather in particularly large groups of fifty to a thousand animals on the fast ice. Since they cannot keep ice holes open with their teeth, they sometimes use the ice holes of the Weddell seals that live in Antarctica all year round . An unusually high number of young crab eaters lose their bearings and migrate inland. Young crab eaters have been found up to 113 km from the sea and even 1100 m above sea level. These seals die on their hopeless migrations, and their mummified carcasses are quite common in the Antarctic ice.
Reproduction and development
The females throw their only young after a gestation period of 11 months (actual gestation period 260 days, plus 80 days of dormancy ) between September and October on the Antarctic ice. The rearing of the young usually takes place on an ice floe and only very rarely on fixed ice. A young is always born; The fact that twin births are possible is known from the discovery of twin fetuses, but no crab eaters with two cubs have been observed in the wild. The cubs have light brown lanugo hair that is replaced two weeks after they are born.
The mother and young animal are in the company of a male who is very likely not the father, but stubbornly defends the female and her offspring against invading other males and also against leopard seals and humans. The male bites the intruder in the head and neck area and tries to prevent him from entering the center of the ice floe.
At the same time, the female does not allow the protective male to get closer than 2 m while it is suckling the young. While the young is suckled, the mother does not consume any food and only feeds on its fat reserves. The baby is suckled for 14 to 21 days, during which time it increases its weight fivefold. In total, the female gives 90 liters of milk from her two teats to the young and loses around 5.6 kg of weight every day. The thickness of the bubbler is reduced from 6.7 cm to 4 cm. During this time, the male consumes less food than usual, but usually does not completely refrain from looking for food.
The sacrifice of the male, who is not even the father of the young animal, is based on the fact that it is allowed to mate with the female as soon as the young animal is independent. The couple then stays together for another two weeks before separating. A year later, the female will give birth to the young from this male and will then be defended by another male.
Crab eaters become sexually mature at three to six years of age and have a previously determined maximum life expectancy of 39 years.
ecology
The most important natural enemy of the crabeater is the leopard seal . Around 80 percent of all crab-eaters have scars from wounds that have been shown to have been inflicted by leopard seals. Young crab eaters in particular are attacked. The high risk is due to the fact that the leopard seals come to the ice floes and prey on the young there. Only 20 percent of young crab eaters survive their first year, and a high proportion of deaths are believed to be from leopard seals.
Another enemy is the killer whale , which chases crab eaters primarily in the water, but also capsizes ice floes in order to eat seals that are resting there. Shrimp eaters are less likely to fall prey to sharks .
In 1955 there was a mass death of crab eaters from an unknown virus whose symptoms resembled distemper .
Taxonomy and systematics
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Phylogenetic system of dog seals according to Higdon et al. 2007
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The shrimp eater was first described scientifically in 1842 by Jacques Bernard Hombron and Honoré Jacquinot under the scientific name Phoca carcinophaga without any indication of the Terra Typica . In 1853 Hombron and Jacquinot added the geographical indication to include “on ice around the South Pole between the South Sandwich Islands and Powell Island .” (»Sur les glaces du Pole Sud, entre les iles Sandwich et les iles Powels, á 150 lieuesde distance de cune de ces iles «). The species name ( epithet ) is often given in the male form carcinophagus , but according to the guidelines of the International Commission on Zoological Nomenclature (ICZN) it should remain female.
The crabeater is the only species of the genus monotypical . Based on molecular biological results from 2007 is the species as of the most basic representative of the Lobodontini combined group of species of crab-eater, Ross Seal ( Ommatophoca rossii ), leopard seals ( Hydrurga leptonyx ) and Weddell ( Leptonychotes weddellii considered), the elephant seals are considered in this view as a sister group of the Lobodontini.
population
No other seal has as many individuals as the crabeater. The total population is estimated at 30 million animals; this means that around every second seal in the world is a crabeater. The population density is 0.5 to 5 individuals per square kilometer, with it being highest at the edge of the pack ice belt.
It is believed that this seal has become increasingly common over the past few decades as more krill become available each year. The collapse of the krill-eating baleen whales caused by whaling seems to be directly related to the population growth of the crab-eaters, as an important food competitor of the seals has disappeared.
Relationship to people
The oldest illustration of a crab eater comes from Pawel Michailow, who accompanied Fabian Gottlieb von Bellingshausen's Russian Antarctic expedition as an illustrator from 1819 to 1821 . However, the animal was not given a name here. This only happened on the French expedition of Jules Dumont d'Urville (1837-1840), on which the naturalists Jacques Bernard Hombron and Honoré Jacquinot described this seal and gave it the name Phoca carcinophaga . The species name carcinophaga means "crab-eating". As early as 1844, John Edward Gray placed the crab eater in its own genus Lobodon (from lobus = "lobe", "tip", and odont = "tooth").
Crab eaters were never exploited on a large scale like other seals. For one, their habitat in the Antarctic pack ice makes it difficult to get at them. Since they raise their young on thin, thin ice floes, seal hunters cannot approach them and kill them as they can with the arctic harp seals . Another reason is the frequent scars from leopard seal attacks, which reduce the value of the hides and pelts.
Shrimp eaters are seldom kept in zoos , as food consisting almost exclusively of krill can hardly be made available. In isolated cases, however, it has been possible to get crab eaters used to fish food in captivity. They then also eat species such as mackerel and sardines, which they would never ingest in the wild, but must first be force-fed before they can accept the new food.
Individual evidence
- ↑ a b Jeff W Higdon, Olaf RP Bininda-Emonds, Robin MD Beck, Steven H. Ferguson: Phylogeny and divergence of the pinnipeds (Carnivora: Mammalia) assessed using a multigene dataset. BMC Evolutionary Biology 7, 2007. doi: 10.1186 / 1471-2148-7-216 .
- ↑ a b Brent S. Stewart: "Crabeater Seal - Lobodon carcinophaga." In: In: Don E. Wilson, Russell A. Mittermeier: Handbook of the Mammals of the World. 4. Sea Mammals. Lynx Edicions, Barcelona 2014; P. 174. ISBN 978-84-96553-93-4 .
literature
- Ronald M. Nowak: Walker's Mammals of the World. 6th edition. Johns Hopkins University Press, Baltimore 1999, ISBN 0-8018-5789-9
- Peter J. Adam: Lobodon carcinophaga . Mammalian Species No. 772, 2005.
Web links
- Lobodon carcinophaga in the endangered Red List species the IUCN 2006. Posted by: Seal Specialist Group, 1996. Retrieved on 12 May, 2006.