seals
| seals | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
A pacific walrus |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Pinnipedia | ||||||||||||
| Illiger , 1811 | ||||||||||||
| Familys | ||||||||||||
The seals (Pinnipedia) are a taxon of aquatic predators (Carnivora) and therefore belong ecologically to the marine mammals . The scientific name "Pinnipedia", derived from the Latin words pinna 'fin' and pes 'foot', means pinniped . Both this term and the term water predators can also be found in specialist literature . In an older biological system , the water predators were compared to the " land predators " (Fissipedia) , which are no longer recognized as taxons .
anatomy
Seals are medium to large mammals that can reach lengths between four and six feet. The weight varies extremely between the species and is between 25 kilograms for females of the Antarctic fur seals ( Arctocephalus gazella ) and more than 4 tons for male southern elephant seals ( Mirounga leonina ). A noticeable sexual dimorphism can often be seen: male elephant seals often weigh up to four times more than their females.
The seal body has a torpedo-shaped shape: the flattened head is only indistinctly separated from the rest of the body by a thick neck, and the tail is only preserved as a rudiment . The limbs are also embedded in the body up to the elbow or knee, so that only the forearm and thigh are exposed. All these properties reduce the flow resistance and thus serve to adapt to life in the water.
Skull and teeth
In the seal skull , the anterior occipital bone , the supraoccipital bone overlaps with the temporal bone , the parietal bone ; the eye sockets are enlarged, while the rostrum, the animal's " snout ", is greatly shortened. Instead of the typical predator teeth, most seals have a rather uniform fish-eating teeth. There are usually one to two pairs of lower incisors, conical, mostly little accentuated canines, and twelve to twenty-four simple, homodontic , i.e. similarly structured molars. The latter have two roots and are pointed; they are therefore less suitable for chewing than for holding onto the prey. Fangs as in the other predators are not found in seals. However, there are numerous deviations, especially with those seal species that have different diets: The canines of walruses are designed as tusks, while the teeth of crab eaters have complicated cusps that, when the jaws are closed, form a close-meshed sieve with which the animals prey on their food, krill .
Spine and limbs
Depending on the family, different parts of the spine are reinforced, this is due to the different locomotion of the animals. The cervical and thoracic vertebrae are significantly increased in ear seals, in which the front fins are the focus , while the lumbar vertebrae are enlarged instead in dog seals that use their hind fins to move . In addition, the articular processes of the vertebrae are greatly reduced, so that they are not as rigidly connected to one another as in other mammals. This flexibility gives the seal body its great maneuverability. This affects the freedom of movement of the limbs due to the lack of a collarbone ( clavicle ) and the small pelvic girdle that is parallel to the spine .
All four legs were transformed into fins in the course of evolution , the rear extremities were shifted to the extreme end of the body. The upper arm bone (humerus), ulna (ulna) and radius (radius) are shorter but more powerful than other predators, and the thigh bone (femur) is flat and wide, so that an effective power transmission in the water is possible. Each of the fins ends in five long, flattened toes that are webbed together; often the first and fifth toes are elongated. A further specialization of the fins was probably only prevented by the continuing need to move on land.
Fur and layer of fat
Seals are usually born with a thick coat, which disappears as they get older and is replaced by a short coat. Only the fur seals also keep older animals than a flashy fur garment consisting of a dense undercoat and about outstanding stiff guard hair is; Walruses have a short, inconspicuous coat of hair. In the case of ear seals, the fur is renewed together with the top layer of skin over a longer period of time, which can be up to a month, while dog seals usually complete this molting process relatively abruptly within a few days.
To protect against cooling down, there is a layer of fat up to ten centimeters thick in some species. This layer also serves as a nutrient store and contributes to buoyancy in the water . It is particularly pronounced in dog seals and walruses. However, it does not protect the fins supplied by a particularly large number of blood vessels .
Internal organs
The seal stomach is a simple elongated tube and is designed to accommodate swallowed prey as a whole. The small intestine, on the other hand, is very complex and long, and in males of the southern elephant seal ( Mirounga leonina ) can reach a length of over 200 meters; all other sections of the intestine are relatively short.
The testicles of the males are no longer externally visible, because they have largely been relocated to the inside of the body ; the only exception are the walruses, in which the sexual organs are particularly easy to recognize during the mating season. The teats of the females are also no longer on the surface: Since young animals can no longer grasp the teats with their mouth, the mother animal has to actively inject the milk into its boy's mouth if necessary.
Sense organs
The sense organs of the seals have to function both under water and on land and are therefore exposed to conflicting demands.
eyes
The eyes are relatively large and allow a good underwater view. They are adapted to the often low light intensity under water by a greatly increased number of rods in the retina , which in contrast to the cones do not allow color vision, but are much more sensitive to light. The sensitivity range varies with the habitat: The maximum is deep-diving species such as elephant seals ( Mirounga ) in the blue range, but at about harbor seals ( Phoca vitulina , moved) who reside primarily in coastal waters in the direction of green. Color vision is only possible to a limited extent with seals due to the limited number of cones. Another adaptation to the low light conditions is the tapetum lucidum , a reflective layer behind the retina that reflects light that has passed through the retina: This means that light that was not perceived the first time it was passed through is possible the second time to register.
Life in water is not only characterized by an often low light intensity, but also a different refraction of light : the cornea has almost the same refractive index as water and is therefore a component of the imaging apparatus under water. In order to compensate for this, the eye lens of seals is almost spherical and therefore has a much higher refractive power. Because the lens and cornea have a refractive effect in the air , seals are very nearsighted on land, where the sense of sight is less important. To do this, they are able to tolerate the high light intensities emanating from sunlit ice surfaces, for example, by constricting the pupil to a narrow vertical slit. The cornea forms the outer edge of the eye. It is constantly moistened with tear fluid to wash away foreign bodies and prevent direct eye contact with salt water. Unlike their close relatives, seals do not have tear ducts.
Although the sense of sight is also of great importance for seals, it is not irreplaceable: With sea lions and fur seals , the males of which often fight bloody territorial fights, it is not uncommon for them to lose sight; the animals are apparently not limited by their blindness and get along with relatively few problems.
Hearing
Externally, the seals' ears are stunted or non-existent; if available, they are closed when diving. However, seals have excellent hearing. The inner ear is only connected to a single skull bone, which prevents the indiscriminate transmission of sound waves through the entire skull; only then is directional hearing possible under water. The lining of the auditory canal and the middle ear allows the internal pressure to be adjusted while diving.
The perceived frequency range differs depending on the medium: In water, seals can perceive much higher tones than humans; on the other hand, hearing on land is less sensitive with roughly the same perception spectrum.
Sense of smell and touch
As with most land carnivores, the sense of smell is very well developed; since the slit-like nostrils are closed underwater, it only works on land. It plays a role especially in encounters with conspecifics: the mother-child relationship is often maintained by the sense of smell; in many ear seals it is used by the males to determine the willingness of the females to conceive.
Another sense is important for orientation in the water: the highly developed sense of touch of the whiskers ( whiskers ) arranged in horizontal rows on the “snout” . Each of these hairs arises in a connective tissue capsule richly supplied with nerve endings and blood vessels. Vibrissae can sense changes in pressure and flow and are probably also used by the animals to estimate their speed. There is also evidence that whiskers are particularly sensitive to low-frequency vibrations that result from the movement of prey. In fact, seals that have lost their whiskers can no longer catch fish on their own and therefore have to starve to death. After all, vibrissae are used for communication, for example, in conflicts of hierarchy - whiskers that are raised often signal a readiness for aggression.
Thermoregulation
Like all mammals, seals are endothermic , which means that their body has an almost constant internal temperature. In order to avoid cooling down in the water and at the same time overheating on land, the animals have developed numerous adaptations.
Even the body size, which usually exceeds that of land-dwelling predators many times over, reduces cooling due to the much more favorable ratio of heat-producing body volume to heat-emitting body surface and can be evaluated as an adaptation to the medium of water. The already mentioned layer of fat directly under the skin is also a good insulator that is independent of the depth of the water due to its lower thermal conductivity. In addition, the fur seals have a waterproof fur, which has a heat-retaining effect mainly due to the air bubbles dissolved in it. However, the insulating layer of air is compressed by the pressure increasing with the water depth and therefore loses its effectiveness during deep dives.
Seals are also able to regulate the flow of blood to their limbs. In this way, you can minimize the energy output via the fins under cold conditions so that the temperature remains just above the freezing temperature. Conversely, special cross-connections between arterial and venous vessels, the arteriovenous anastomoses (AVA), allow increased blood flow in superficial layers of skin in a warm environment. In fur seals, they are only present in the fins and the loss of heat through these limbs is the only way to cool down. On land, the animals therefore often also beat their fins in order to maximize the energy exchange with the environment through the air flow generated. Another possibility is to wet the fins with urine in order to extract energy from the body through the evaporative cold.
Both dog seals and walruses, on the other hand, have arteriovenous anastomoses over the entire body surface, so that they can regulate the blood circulation and thus the heat release or absorption in a targeted manner. In this way, the animals are able to warm themselves up, even at low air temperatures, by the energy released by the absorption of solar radiation. In sunbathing walruses, this effect can be seen particularly clearly due to the lack of hair on the basis of the pink skin color.
In addition, some seals use behavior-based thermoregulation: if there is a threat of overheating, monk seals ( Monachus ) return to the water. This also includes the fact that the energy-intensive moulting, which is associated with reduced protection against cooling, usually takes place on land, with numerous animals often laying close to each other in order to reduce the heat release to the environment.
Getting around in the water and adapting to diving
In the water seals show the advantages of their physique. Propulsion is generated by the front fins in the case of the ear seals and by the hind fins in the case of walruses and dog seals. In doing so, they developed some of the most energy-efficient methods of locomotion in the animal kingdom.
Although seals need to come to the surface to breathe, they can remain underwater for a considerable amount of time. When diving, the lungs collapse and the air they contain is expelled through the mouth or nose. In this way, there is hardly any free gas in the seal body when diving and therefore cannot lead to the formation of bubbles in the blood when surfacing, as with human divers. All of the oxygen available during the diving process must therefore be in bound form. The blood volume and the total number of red blood cells are increased in seals, as is their hemoglobin content , which leads to a significantly increased oxygen storage capacity compared to purely terrestrial mammals. The muscle tissue of the animals is also significantly enriched with the oxygen-storing protein myoglobin compared to land mammals and tolerates large amounts of carbon dioxide (CO 2 ).
In addition, the seals' heartbeat slows down considerably when diving. The heart's activity can be reduced from a normal hundred beats per minute to up to four beats, while at the same time the blood supply to organs that are not immediately vital to life is restricted and the body temperature is lowered. These measures serve to reduce the oxygen consumption during diving. The reduction in heartbeat and vasoconstriction are usually not as pronounced as would be expected with a regular diving reflex . In addition, seals can regulate your heartbeat in anticipation of the expected duration of the dive.
Despite these adjustments to oxygen storage and rationing during diving, seals' cerebral neurons and cardiac muscle cells are regularly exposed to longer periods of hypoxia. Neurons from the brain of the collapsible cap, for example, last over ten minutes under hypoxic conditions without long-term damage, while neurons from mice can be severely damaged after just five minutes. The basic mechanisms of this hypoxia tolerance are largely unknown.
Some seals, such as elephant seals, can stay underwater for up to two hours at a time without surfacing, and can reach depths of up to 1,500 meters. Most species, however, do not reach such record levels. This is primarily due to the greater body volume of the elephant seals compared to these species and the resulting greater storage capacity for oxygen. Most seal dives are within the aerobic diving limit of the species in question. This can minimize the amount of time a seal needs to recover on the surface of the water after each dive. This allows seals to spend up to 90% of their day underwater.
Getting around on land
Seals seem rather clumsy on land. There are differences between the ear seals and dog seals. While the former have kept strong hind limbs with which they can support the body and also carry out activities such as personal hygiene, the hind legs of the dog seals are largely useless on land, so they have to "crawl" on their stomach and pull themselves forward.
distribution and habitat
Almost all seals inhabit the sea. Since they have to come ashore again and again for many activities, they do not stray too far from the coast and are therefore not found on the high seas.
Only a small number of seals occur (1) optionally, (2) with preference as a subspecies or even (3) permanently as endemic in inland waters: (1) The common seal , predominantly a marine animal, also lives on lake shores in Canada . (2) Two subspecies of the ringed seal are mainly in freshwater before that Ladogaringelrobbe ( P. h. Ladogensis ) in Russian Lake Ladoga and Saimaa ringed seal ( h P.. Saimensis ) in Finnish Saimaa Lake. (3) Two endemic species live exclusively outside of the sea, the Baikal seal ( P. sibirica ) and the Caspian Seal ( P. caspica ). The most likely explanation is inland migration of the Arctic ringed seal ( Pusa hispida ) during a cold period around 400,000 years ago, which corresponds to its genetic distance from the Baikal seal. For this, the ancestors of the Baikal seal would have to have traveled 3800 km from the Arctic following the Angara . However, during severe cold periods there was always a connection to the (currently non-existent) glacier reservoir, called Komisee, last about 60,000 to 50,000 years ago. In the case of the Caspian seal, there is no river connection between the Caspian Sea and the Arctic Ocean in the current interstadial , but there was a connection to the Black Sea.
The majority of seals live in polar and sub-polar latitudes. The seas of the Arctic and Antarctic have a remarkable wealth of species and shapes. Here many seals form large colonies on the coasts of uninhabited islands. On the other hand, the number of species decreases rapidly towards the temperate seas, and there are almost no seals in the tropics. Here, too, there are exceptions, for example the monk seals and the Galápagos fur seal . Large regions in which there are no seals at all are the coasts of tropical Africa, the Asian coasts of the Indian Ocean and the island world of the western Pacific . It is characteristic of almost all distribution areas that the water temperature remains below 20 ° C all year round; the monk seals are the only exception to this rule.
There are only three species of seals on the coasts of the North and Baltic Seas : the harbor seal , the gray seal and the ringed seal . The harbor seal is ubiquitous in the North Sea, but an extreme rarity in the Baltic Sea; Gray seal colonies can be found on German soil on the Jungnamensand west of Amrum and on Heligoland , outside of the rearing of young on all North Sea coasts and rarely on West Pomeranian Baltic coasts; The ringed seal lives in Finland and Gulf of Bothnia in the Baltic Sea and does not arrive at German coasts.
Way of life
In contrast to whales and manatees , which have completely migrated to aquatic life, seals lead an amphibious way of life. Mating and young rearing takes place on land. Although seals can sleep on the surface of the water, they often come to the coast to rest.
nutrition
All seals are carnivores. The overwhelming majority of the species feed on fish . But some have developed special ways of life: Krill forms the basis of food for the crabeater , the walrus searches the sea floor for snails and mussels , squids form part of the diet of elephant seals , while the leopard seal hunts penguins and smaller seals. Small prey are usually swallowed as a whole underwater, while larger food is brought to the surface of the water, where individual pieces may be bitten off. Young animals in particular are dependent on an abundant supply of food, as their smaller body size means they have an unfavorable ratio of body surface area to volume and therefore have to compensate for greater heat losses. Healthy adult animals, on the other hand, are able to survive longer periods of fasting, not least because of their fat layer under the skin.
Gastroliths are known from the stomachs of various species of seals and sea lions. The function of the stomach stones is still largely unclear, both the crushing of the food in the stomach and the reduction in buoyancy in the water are plausible .
Social behavior
Most seals are sociable. Solitary species like the Ross seal are the exception. Seals come together to form colonies, especially for rearing young, which can range in size from a few individuals ( gray seals ) to several million animals ( southern fur seals ) . However, as a result of the massive slaughter of previous centuries, very large colonies have become rare.
Sound behavior
Seals communicate aloud using clicks and singing whistles. Larger seals develop a wide range of sounds like a long, deep roar. One species of seal (first seen at the Hoover Seal , Boston Aquarium ) is known to mimic human sounds.
Reproduction
The breeding season is typically in spring or early summer. In most species, the males establish territories from which they try to keep competitors away. In the rival fights that arise, weaker males inevitably lose out, so that a dominant male can usually claim several partners for himself.
The females, mostly pregnant from the previous year, sometimes arrive in the colony weeks later than the males. There they look for the best places to raise their offspring, which are usually occupied by the most assertive males; there they give birth to their young. Dog seals suckle it for a few days or several weeks, depending on the species, and then mate with the owner of the territory after weaning. The relationship between mother and young is practically over at this point. In the case of ear seals, on the other hand, contact persists beyond the mating of the mother, which usually takes place around a week after the birth of their offspring. This only becomes independent after about four to six months, but can occasionally even be supplied with breast milk after the birth of the next boy.
After fertilization, the embryo only develops to the blastocyst stage, a still undifferentiated hollow sphere of cells. Only after a period of dormancy does the blastocyst embed itself in the maternal wall of the uterus and form a placenta . Only through this system can female seals accomplish birth and re-fertilization in the same period of time.
The gestation period for seals is eight to fifteen months, depending on the species. All species typically give birth to a cub that is born either head first or tail first. Twin births occur but are very rare; the mother's milk is almost never enough to raise both animals. Newborns have a special downy birth fur called lanugo , which is often different from the fur color of the adult animals. However, some species of dog seals change it already in the maternal uterus, while most ear seals do not take off their young clothes until they are two to three months old. All young animals do not yet have a sufficient layer of fat to guarantee buoyancy and water repellency. Although theoretically they could swim from the start, they do not go into the water for the first time until they are a few weeks old. Since the young are largely defenseless at the beginning of their life, growth takes place very quickly.
Predators and life expectancy
The seals' enemies are mainly sharks and killer whales . The latter are so specialized in seal hunting in Patagonia that they even throw themselves on the beach to catch the fleeing seals. In the Arctic , the polar bear appears as an important enemy of the seals, in the Antarctic the leopard seal, which is itself a species of seal that specializes in hunting relatives.
Most species have a life expectancy of around thirty years. The walrus often lives more than forty, and many ear seals not more than twenty years. With seals that live in herds, the males often die much earlier than the females because they exhaust themselves in the territorial fights or suffer serious injuries. Theoretically, the smaller seal species also have a high life expectancy - the harbor seals, for example, over 30 years - which they can seldom reach due to natural enemies and human influences.
Tribal history
Modern styles
Traditionally, seals were either viewed as a separate order or they were contrasted with land carnivores as a subordination of water predators . At least the latter classification is unusual today. The seals evolved from land carnivores, more precisely from canines ; they are therefore also to be found within the canine species.
On the basis of morphological studies, some zoologists still assumed in the 1990s that the seals form two different lines of development. It was believed that the ear seals were descended from bear-like ancestors and the dog seals from otter-like ancestors. Accordingly, the two seal groups would have developed independently of each other. Following this hypothesis, seals would be polyphyletic , i.e. a pure form taxon that would have no justification as a systematic group of mammals.
However, since the 1990s this hypothesis has been pushed back in molecular genetic analyzes. In 1996, Olaf RP Bininda-Emonds and AP Russell cited strong evidence of seal monophyly; later studies have confirmed their results.
Since the 19th century, a relationship between seals and bears and their relatives has been believed to be likely. However, the exact position of the seals in the zoological system is still unclear, so that the sister group of seals is not yet known beyond all doubt.
With Malcolm C. McKenna and Susan K. Bell the seals appear as a sister group of the bears and this within a superordinate taxon Ursida:
| Ursida |
|
||||||||||||
|
|
The Amphicyonidae are an extinct group that lived from the Eocene to the Miocene ; the Ursoidea include the bears and the also extinct Hemicyonidae (Eocene to Pliocene ); and Phocoidea is the term used synonymously for Pinnipedia by Malcolm C. McKenna and Susan K. Bell. The hypothesis shown here is the most widespread, but there are also contradicting views in which, for example, the marten or the little panda are seen as sister groups of the seals.
Fossil representative
.jpg)
The first fossil- preserved seal-like animals date from the late Oligocene around 27 to 25 million years ago, including the otter-like Puijila and the genera Enaliarctos and Pacificotaria , which are part of the Enaliarctidae family . This long puzzling group has recently become better known through the discovery of complete skeletons. The animals of the genera Enaliarctos and Pacificotaria were already seal-like, but still had front and rear legs suitable for walking on land. Whether the Enaliarctidae or the also extinct animals of the genus Pteronarctos were real seals is a question of definition. A. Berta and AR Wyss denied this in 1994 and combined seals and Enaliarctidae to form a higher taxon Pinnipedimorpha:
| Pinnipedimorpha |
|
||||||||||||||||||||||||
|
|
The seals' biogeographical origin was very likely in the North Pacific, probably on the west coast of the North American continent. The modern ear and dog seal taxa, which first appeared in the Miocene , probably originate from this area . However, this is only documented by fossils for the ear seals and walruses, the earliest species of which all come from North Pacific sites; the first dog seal fossils, on the other hand, are only known from former Atlantic waters off the east coast of the USA.
Systematics
The 33 seal species living today ( Japanese sea lions are considered extinct) are traditionally divided into three families :
- Dog seals (Phocidae) have no externally visible ears; their leg fins are pointed backwards so that they cannot be used when moving on land. In the water, however, they provide the animals' propulsion in alternation. After the Caribbean monk seal became extinct, 18 species still exist. The dog seals include a variety of smaller seals such as common seals or gray seals , but also the giant elephant seals .
- Eared seals (Otariidae) have small external ears and can use their leg fins in their original position under the body to be able to move better on land. Their forefins are the main source of propulsion in the water. The 15 species in the group are mainly large colony-forming seals such as sea lions and fur seals.
- Walruses (Odobenidae), today only represented by one species, are primarily characterized by the conspicuous tusks, the greatly enlarged canines of the upper jaw. They can put their hind fins, which are more like those of the dog seals, under the body like ear seals.
The ear seals are sometimes considered to be the more "primitive" group because of their visible outer ears, but the fossil record of the dog seals is as old as that of the ear seals.
Eared seals and walruses are mostly viewed as closely related clades , although the walruses mediate between the two groups in numerous traits. Malcolm C. McKenna and Susan K. Bell, contrary to this popular belief, have classified walruses as a subfamily of dog seals. This is a minority view, however, as most zoologists see strong evidence of a common taxon of ear seals and walruses, sometimes called otarioidea:
| Seals (Pinnipedia) |
|
||||||||||||
|
|
Walruses (Odobenidae)
|
People and seals
.jpg)
The relationship between humans and seals is highly dependent on the region in which a human culture was located. It probably began as early as the Paleolithic, from which engravings in seal bones and teeth are known. From the culture of the Eskimos seals are still hardly imagine, they form not only an important source of food, but also provide skin for leather and sealskin for furs . In the past, bones were also used to make tools, tendons for bows and fat for heat and light giving oil lamps.
Seals also served as a source of food for other peoples. The Māori of the South Island of New Zealand and the Aborigines of the Australian south coast hunted fur seals and used them in similarly diverse ways. Fur seals were also popular prey for the indigenous people of the South American Tierra del Fuego .
In contrast, the ancient kingdoms of the Mediterranean region had little contact with seals, as only one species, the Mediterranean monk seal , is found here, which was probably a rarity in ancient times. Aristotle provided a description of this seal, which is therefore the earliest representative of the animal group that has been preserved in written records. It is conceivable that monk seals lying on the coast were the model for the sirens in Greek mythology, but it is within the range of speculation.
None of the subsistence hunts mentioned presumably had a significant long-term impact on the stocks of the affected seal populations. Seals can die from plastic bags because they are mistaken for jellyfish.
Modern mass hunt
The great age of the seal hunters began in the late 18th century, although ships had been sent out for the sole purpose of slaughtering seals since the 16th century. Throughout the 19th century, ships were sailing in the Arctic Ocean and docking on islands to kill the large seals that lived in colonies there. The fur seals were particularly affected, and their fur was considered particularly valuable. The seal hunts reached a scale that is unparalleled among the extinctions in the animal kingdom. Every summer about fifteen ships camped at the same time on the Juan Fernández Islands , whose crews killed 250,000 fur seals lying on the coast every year and thus completely destroyed one of the largest animal colonies in the world within fifteen years. The Antarctic fur seal, which was home to millions of animals on the coasts of sub-Antarctic islands, was almost wiped out by seal hunters crisscrossing the Southern Ocean between 1800 and 1830. The South Shetland Islands , for example, were not discovered until 1819, but two years later the five hundred thousand fur seals that lived here were killed down to the last specimen. It is an astonishing fact that only one species, the Caribbean monk seal ( Monachus tropicalis ), became extinct during these extermination excesses . However, almost all seals have declined sharply, and some species that used to form huge colonies now only live in tiny groups on the coasts.
Today other seal species are mostly killed, as the last remaining fur seals are mostly under protection. It is above all the harp seal whose young are killed to gain fur. Every year these killings are accompanied by protests by animal rights activists who use the faces of baby seals to publicize them. In contrast, the traditional hunting of adult animals by the Eskimos is mostly accepted by nature conservationists. Proponents justify the need to decimate seals, among other things, arguing that an uncontrolled seal population is plundering fish stocks; Marine biologists assume, however, that the decline in schools of fish is not caused by the few remaining seals, but by the deep sea fleets of the industrialized countries.
In 1972, the Convention on the Conservation of Antarctic Seals, or CCAS, was concluded as an additional protocol to the Antarctic Treaty .
On May 5, 2009, the European Parliament passed a trade ban on numerous products made from seals such as seal skins and omega-3 capsules made using seal oil . Narrowly limited exceptions allow trade in seals hunted by Eskimos , for which a certificate of origin is required. The ban should come into force before the next 2010 hunting season. One of the main arguments is not the economic use of the seal population per se, but the manner in which the animals are slain, which is classified as unsuitable for animal welfare. Canada and Norway , which are mainly involved in the trade in these products, lodged a complaint with the World Trade Organization , thereby ensuring that the embargo was suspended until at least 7 September 2010.
In the EU, Regulation (EC) No. 1007/2009 of the European Parliament and of the Council of 16 September 2009 with a ban on placing on the market for seals (and parts of them such as skins ) and products made from seals (such as oils) applies directly . . The placing on the market is defined here as importing into the common market, through which provision is made for third parties against payment; there are some exceptions that are linked to the type of seal hunt and its evidence. The implementation of the ban is regulated in Germany by the Animal Products Trade Prohibition Act .
Zoos and circuses
Seals are also kept in zoos and occasionally in circuses . In the zoo, the seal feedings are often a special attraction. The walrus Antje from the Hagenbeck zoo became famous and became the logo of the NDR . In circuses, dolphinariums and other animal shows, the Californian sea lion is preferred and can be trained to perform tricks with balls and hoops.
However, many animal rights activists criticize the fact that seals in the zoo cannot be kept in a species-appropriate manner - this is especially true for the ear seals that are often kept in zoos , which live in large colonies in the wild and where territorial warfare is part of the behavioral repertoire. In particular, the water basins in which the animals are kept are considered too shallow to offer the animals approximately natural conditions; in addition, the water is often chlorinated.
Military use
The efforts of the US Navy to include trained sea lions in military planning are relatively new . The animals are trained to track down sea mines , to warn of enemy divers and to retrieve objects that have been lost in deep water. The Swedish Navy carried out similar experiments during World War II.
literature
- Ronald M. Nowak: Walker's Mammals of the World . 6th edition. Johns Hopkins University Press, Baltimore 1999, ISBN 0-8018-5789-9 (English).
- Bernhard Grzimek: Grzimeks animal life . Volume 12 (Mammals 3). Bechtermünz, Augsburg 1979, 2000, ISBN 3-8289-1603-1 .
- C. McKenna, Susan K. Bell: Classification of Mammals. Above the species level . Columbia University Press, New York 2000, ISBN 0-231-11013-8 .
- Rüdiger Wandrey: The whales and seals of the world . Franckh-Kosmos, Stuttgart 1997, ISBN 3-440-07047-6 .
- A. Berta, AR Wyss: Pinniped phylogeny. In: Contributions in marine mammal paleontology honoring Franck C. Whitmore, Jr. Proceedings of the San Diego Society of Natural History. 29, 1994, pp. 33-56. ISSN 1059-8707
- Olaf RP Bininda-Emonds, AP Russell: A morphological perspective on the phylogenetic relationships of the extant phocid seals (Mammalia: Carnivora: Phocidae). In: Bonn Zoological Monographs. 41, 1996, pp. 1-256. ISSN 0302-671X
Individual evidence
- ↑ Coats and jackets made from walrus. In: The fur trade. No. 5, Leipzig / Vienna 1958 p. 231.
- ^ Frank E. Fish: Transitions from Drag-based to Lift-based Propulsion in Mammalian Swimming . In: American Zoologist . tape 36 , no. 6 , December 1, 1996, ISSN 0003-1569 , pp. 628–641 , doi : 10.1093 / icb / 36.6.628 ( oxfordjournals.org [accessed December 5, 2016]).
- ↑ GL Kooyman, WB Campbell: Heart rates in freely diving weddell seals, leptonychotes weddelli . In: Comparative Biochemistry and Physiology Part A: Physiology . tape 43 , no. 1 , September 1, 1972, p. 31-36 , doi : 10.1016 / 0300-9629 (72) 90465-3 ( sciencedirect.com [accessed December 5, 2016]).
- ↑ a b Randall W. Davis: A review of the multi-level adaptations for maximizing aerobic dive duration in marine mammals: from biochemistry to behavior . In: Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology . tape 184 , no. 1 , January 1, 2014, ISSN 1432-136X , p. 23-53 , doi : 10.1007 / s00360-013-0782-z , PMID 24126963 .
- ^ Claude Lenfant, Kjell Johansen, John D. Torrance: Gas transport and oxygen storage capacity in some pinnipeds and the sea otter . In: Respiration Physiology . tape 9 , no. 2 , May 1, 1970, pp. 277–286 , doi : 10.1016 / 0034-5687 (70) 90076-9 ( sciencedirect.com [accessed December 5, 2016]).
- ↑ Randall W. Davis, Terrie M. Williams: The marine mammal dive response is exercise modulated to maximize aerobic dive duration . In: Journal of Comparative Physiology A . tape 198 , no. 8 , May 15, 2012, ISSN 0340-7594 , p. 583-591 , doi : 10.1007 / s00359-012-0731-4 ( springer.com [accessed December 5, 2016]).
- ↑ J. Qvist, RD Hill, RC Schneider, KJ Falke, GC Liggins: Hemoglobin concentrations and blood gas tensions of free-diving Weddell seals . In: Journal of Applied Physiology (Bethesda, Md .: 1985) . tape 61 , no. 4 , October 1, 1986, ISSN 8750-7587 , p. 1560-1569 , PMID 3096941 .
- Jump up ↑ Lars P. Folkow, Jan-Marino Ramirez, Stian Ludvigsen, Nicolo Ramirez, Arnoldus S. Blix: Remarkable neuronal hypoxia tolerance in the deep-diving adult hooded seal (Cystophora cristata) . In: Neuroscience Letters . tape 446 , no. 2–3 , December 3, 2008, pp. 147–150 , doi : 10.1016 / j.neulet.2008.09.040 ( sciencedirect.com [accessed December 5, 2016]).
- ↑ GL Kooyman, EA Wahrenbrock, MA Castellini, RW Davis, EE Sinnett: Aerobic and anaerobic metabolism during voluntary diving in Weddell seals: Evidence of preferred pathways from blood chemistry and behavior . In: Journal of comparative physiology . tape 138 , no. 4 , ISSN 0340-7594 , p. 335–346 , doi : 10.1007 / BF00691568 ( springer.com [accessed December 7, 2016]).
- ↑ Lars P. Folkow, Arnoldus Schytte Blix: Diving behavior of hooded seals (Cystophora cristata) in the Greenland and Norwegian Seas . In: Polar Biology . tape 22 , no. 1 , ISSN 0722-4060 , p. 61-74 , doi : 10.1007 / s003000050391 ( springer.com [accessed December 7, 2016]).
- ↑ Miina Auttila, Tuula Sinisalo, Mia Valtonen, Marja Niemi, Markku Viljanen, Mika Kurkilahti, MerviKunnasranta: Diet composition and seasonal feeding patterns of a freshwater ringed seal (Pusa hispida saimensis) . In: Mar. Mammal Sci. , Volume 31, No. 1, January 2015, pp. 45-65, doi : 10.1111 / mms.12133
- ↑ Tero Sipilä, Heikki Hyvärinen: Status and biology of Saimaa (Phoca hispida saimensis) and Ladoga (Phoca hispida ladogensis) ringed seals . In: J NAMMCO Scientific Publications , Volume 1, 1998, pp. 83-99, doi : 10.7557 / 3.2982 ( PDF ).
- ↑ Tara Lynn Fulton, Curtis Strobeck: Multiple markers and multiple individuals refine true seal phylogeny and bring molecules and morphology back in line . In: Proceedings of the Royal Society B , Volume 277, 2010, pp. 1065-1070, doi : 10.1098 / rspb.2009.1783 .
- ↑ Olga Maslenikova, Jan Mangerud: Where was the outlet of the ice-dammed Lake Komi, Northern Russia? In: Global Planetary Change , Volume 31, No. 1, November 2001, pp. 337-345, doi : 10.1016 / S0921-8181 (01) 00128-X ( PDF ).
- ↑ January Mangerud, Valery I. Astakhov, Andrew Murray, John Inge Svendsen: The chronology of a large ice-dammed lake and the Barents Kara Ice Sheet advances, Northern Russia . In: Global Planetary Change , Volume 31, No. 1, November 2011, pp. 321–336 ( PDF ).
- ^ Language of the North Sea seals
- ↑ Katharina Kramer: "Get out of there!" Hoover, the talking seal . In: Spiegel online. Retrieved October 23, 2012.
- ↑ Plastic bags: harmful waste product. In: Ostthüringer Zeitung. otz.de , 2010.
- ↑ Questions & Answers about the seal hunt in Canada. ( Memento from August 2, 2012 in the web archive archive.today ) on: greenpeace.de , 2011.
- ↑ Decision of the European Parliament: The trade in seal products is prohibited. ( Memento from May 8, 2009 in the Internet Archive ) on: Tagesschau.de , May 5, 2009.
- ↑ Seal skins can still be sold despite embargoes. In: time online. August 20, 2010.
- ↑ Föreningen Armé- Marin- och Flygfilm , follow the link " Sök " (search), enter " Sälar " (seals), top keyword, visited: April 30, 2008.
