See also:
|
The harbour seal and the grey seal are normal inhabitants of the Dutch coastal waters. They are protected from human activities through various directives and Conventions. Ringed seals, harp seals and hooded seals swim in more northerly seas but are sometimes found in the southern North Sea, having wandered too far south. Seals belong to the pinnipeds. Seals consume primarily fish. They use their whiskers for locating their prey in these predominantly turbid waters. Seals can feel the slightest movements in the water, such as displacement caused by a swimming fish. They can determine where the fish is swimming and snatch it with their sharp teeth. Seals do not have a preference for one specific fish species. They eat whatever fish is found in their area at the time, which can vary from season to season. Distribution and counts
The numbers and communal areas of the seals in the Wadden Sea region are well documented. Observations made from boats and airplanes have been providing a reliable picture since the 1960s. Scientists IMARES count the seals in the Dutch Wadden Sea eight times per year by making photos of the populations. Studies have also been made by providing seals with transmitters. These studies have shown that around two-thirds of the total number of seals are actually counted from the airplane (when only seals visibly present on the sandbanks are counted). The other third is apparently under water during the count, so that half of what is counted must be added for the final population estimate. Of the seals that inhabit the international wadden region, the large majority are harbour seals, numbering around 21,000 in 2005. However, harbour seals also inhabit other waters, and in the North Sea area, they are found around the Scottish islands, in the Wash, along the English, French and Belgium coasts, in the Danish Skagerrak and along the southern coast of Norway. Grey seals are found primarily around the Scottish islands, along the British east coast and in Cornwall. In December 1999, there was even a young seal seen in the Thames beyond London. Environmentalists see this as proof that the Thames has become less polluted. Up till the beginning of the 19th century, it was normal to see seals and dolphins in the Thames. In the Dutch Wadden Sea, a colony of grey seals was established in the early 1990s. In the meantime, it has expanded to the largest in the Wadden Sea, where 1500 were counted in 2005. The largest groups are located west of Terschelling. Small groups or individuals are sometimes seen elsewhere. Only the German islands of Helgoland and Amrum have larger colonies, counting more than a hundred animals. Satellite observations of seals with transmitters show that grey seals from the Wadden Sea can swim all the way to Northern Scotland. This shows that the seals are not dependent upon the Wadden Sea and that it is difficult to count the entire population.
With a top speed of 35 kilometres an hour and a cruising speed of 6 to 7 kilometers per hour, one can classify seals as good swimmers. The front flippers serve as paddles; the body and hind fins provide the propulsion. A seal swims on its back just as readily as on its belly, right side up or upside down. The body is fully adapted to speed under water: it has a torpedo-shaped body and protrusions such as ear lobes are absent. The nostrils are continually closed while swimming and will only open when the seal comes to the surface for a breath of air. The North Sea is not deep enough but seals can easily dive to depths of a few hundred meters. During the first few minutes, they swim actively downwards, after which they go into a kind of gliding flight while they sink even deeper. During this gliding flight, the seals can move at a speed of 1 meter per second (more than 3.5 kilometer per hour) while they use only half as much oxygen as when they actively swim. Only cetaceans are capable of making such gliding dives. During ascension, the seals can pump out the inhaled air from the air sacs, whereby no oxygen ends up in the blood. When rising from large depths, nitrogen can form air bubbles in the blood. This is sometimes deadly for scuba divers, known as the bends or the caisson disease. On land
In contrast to all the adaptations for life in the sea, the seal is clumsy on land: it cannot walk since the hind fins lie in extension of the body. Sea lions, on the contrary, can use their back fins more or less as 'hind feet'. This makes it easier for them to 'walk' much. Seals drag their body over the ground with the help of their front flippers, a movement referred to as hobbling. However, you'd be amazed how fast they can cover a short distance. Sleep
Seals sleep in the water as well as on land. In the water, they sleep floating in a standing position, like a fishing bobber, or floating horizontally on the surface. Because they are sleeping and not actively swimming, they can stay under water much longer than when hunting for food. There are known incidents where seals stay under water up to half an hour, however on the average, their stay is not longer than fifteen minutes. Diving
In order to be able to dive deeply and for a long period of time, the seal's body has been adapted to living under water. Its blood can take up much more oxygen than man's blood, due to the high level of the oxygen-binding protein hemoglobin in the blood and myoglobin in the muscles. Both proteins can also bind oxygen better than in human bodies. Furthermore, seals have relatively more blood (12% body weight) than man (7%). During a dive, a seal can decrease its heartbeat enormously, from forty to less than one beat per minute, whereby decreasing the need for oxygen. Once above water, the heartbeat rises to 120 beats per minute in order to provide the organs with sufficient oxygen. A layer of fat keeps the animal warm. In the flippers, which are less insulated, the cold blood from veins is warmed up by warm blood from arteries because the blood veins are intertwined with each other (see illustration). This prevents the animal from cooling down. Wandering guest from northern regions In addition to the harbour seal and the grey seal, both indigenous to the southern North Sea, an occasional arctic seal species will wander into these regions. Ringed seals are the most common. They come primarily from the northern Baltic Sea. The harp seal is the second most common. In 1987, there was talk of an invasion of harp seals in the southern North Sea, probably due to a lack of food in the Barents Sea. Beaching of hooded seals, bearded seals and walruses are much rarer. In 1986, several hooded seals washed ashore on the coasts of France, Belgium and the Netherlands. This 'mini' invasion was possibly related to a hunting party on the island of Jan Mayen in the Northern Arctic Sea. A unique event was the stranding of a female bearded seal on 27 June 1988 in the harbour of Yerseke in Zeeland. Furthermore during the 20th century, there are accounts of a total of 6 walrus beachings, the last one on Ameland in January 1998. Details of strandings can be found by the descriptions of the species. Human threats Up till the 1970s, hunting was the greatest threat for seals in the North Sea region. After the large-scale seal hunt ended, seals were still threatened, but the cause was a flow of polluting waste materials from land to sea and from discharges and accidents at sea. In addition, disturbances from shipping and recreation became a problem. Present threats include seals swimming after fish into fykes and standing rigging and ending up drowning.
A well-known example of poisoning is the influence of PCBs upon the reproduction and immunity systems of the seals in the Wadden Sea. Disturbing the peace
Another problem for seals in the North Sea and Wadden Sea is the increasing pressure in their haul-out areas, for example, from tourists and military activities. Especially during the summer when the pups are born, this disturbance can form a threat for the seals. The newly born pups cannot miss their mothers during the first few weeks. They drink milk from their mothers during the hours that the sandbanks are above water. If mother and child are continually chased into the sea by tourists, then the pup will not get enough to drink, which can have serious consequences. The young animal will grow weak and be more vulnerable to diseases or more readily contaminated with parasites. Sometimes, the mother and pup get separated from each other. During the summer season, the water police must take action against tourists around four times a day due to disturbance of the seals lying on the sandbanks. Seals versus fisherman The amount of fish consumed by seals is considerable. Therefore, the seal is considered a threat to the fisheries. In the past, premiums were offered for shooting seals due to the damage they supposedly caused. This argument is still used in Scotland, Norway and Canada to rectify culling the seals. Locally, seals can cause problems for fyke and standing rigging fisheries in particular. Not only do they 'steal' away fish, they can also damage the nets and the catch. Even the Scottish and Norwegian salmon nurseries are regularly visited by grey seals that eat salmon. Exact data as to the damage is difficult to give since there are large differences between what the fish farmers say (enormous) and the nature-lovers (damage more or less negligible in relationship to the profit of the nurseries). Neutral sources say the average annual loss lies between 1 and 4% of the the total profit. Another problem is the competition between seals and fisheries for the fish. Studies of the stomach content and excrement has clearly shown that the diet of the harbour seal consists of fish species that for 75% are interesting for commercial fishing. Ninety percent of the fish consumed by grey seals is fished by fishermen. The study was performed by Scottish and Danish researchers, and they consider lesser sandeel (50% diet of the grey seal) to be a commercially important species. The same researchers claim that the seals around Scotland eat 30% of the cod that are caught and around 5% of the lesser sandeel. Other sources calculate that the seals eat a percentage of 2 or 3 of the total cod yield. One can say that the seals consume an average amount of around 10% of the total catch in the North Sea. That percentage is lower for the Dutch situation. All Dutch harbour seals eat an amount of fish per year equivalent to 3.4% of what the fisheries bring on land. The seals eat relatively lots of young flounder, a species which is hardly commercially interesting. Studies on food habits of grey seals are not yet ready, so that no comparison can be made. Experiences with management hunting as done in Scotland are not very positive. The hunters shot mostly female seals by the seal nurseries, while the salmon robbers are usually young males. In addition, the complex ecosystem in which the seals live must be taken into consideration. Shooting the seals may lead to an increase in cod, but cod themselves eat whiting, haddock and herring, so by decreasing the number of the seals will indirectly put more pressure on these species. Obligatory retaining net in fykes
The fish which swim into a fyke form an attractive prize for a seal. The seal swims into the fyke to catch the fish. Once in the fyke, the seal cannot get out and drowns. In the Netherlands since 1994, all fykes in tidal waters are required to be equipped with a retaining net, specifically to keep out seals. This retaining net is a large-meshed net in the 'throat' of the fyke, through which eel and other fish can swim, but not seals. Nevertheless in 2000, there are still seals drowning in fykes which were not equipped with the required retaining net.
The harbour seal and grey seal are both on the Red List for mammals. Since 1978, a conference is organized every two years between the ministers of the three Wadden Sea countries, The Netherlands, Germany and Denmark. During the Wadden Sea conference in 1988 in Bonn, the three countries signed the Seal Treaty, which regulates the protection of the seals in the Wadden Sea. Beside the ban on hunting, it was agreed to establish protected areas for the seals in the Wadden Sea. Seal reservations were designated to prevent disruption to resting and nursing seals. These resrevations are also closed areas in the summer, when the seal pups are birthed and nursed. In other European waters, the harbour seal and grey seal fall under protection of the EU Habitat Directive (Appendix ll and V), the Bonn Convention (Appendix ll) and the Bern Convention (Appendix lll). Seal rehabilitation
Sometimes, young or sick seals are found along the coast. These seals can be brought to special centres, where they are cared for. Once rehabilitated and healthy, they are released back into the wild. There are five such centres in the Wadden Sea region. The oldest professional seal rehabilitation center is Ecomare on Texel. The centre's predecessor, the Texels Museum, began in 1952 as a first to take care of seals in a professional manner and be successful. The Artis Zoo in Amsterdam had been attempting to rehabilitate seals since 1925, but had not as yet devised a successful system. Nowadays, Ecomare cares for and releases twenty to thirty seals a year.
The other four centers are: in the town of Pieterburen in the Province of Groningen, founded in the early 1970s; two centres in Germany, one in Norden-Norddeich and one in Friedrichskoog; and one in Esbjerg, Denmark. The seal sanctuary in Norden-Norddeich cares for 20 to 50 mammals yearly. In addition to seals, they also care for various whale species. The Fiskeri-og Søfartsmuseet in Esbjerg, Denmark is equipped for helping seals although, with the exception of scientific study, that has not happened since 1982. This has to do with the Danish ban on releasing animals back into nature which have been held in captivity. Those animals unable to survive in the wild are shot or brought to zoos. There are also several sanctuaries outside of the wadden region. A seal sanctuary was founded in 1998 in the Belgium town of Blankenberge and there are a couple of sanctuaries along the British coast. In 2005, 29 pups were cared for in Blankenberge. There is a lot of discussion concerning seal care: is it necessary? Why do we do it? Are we creating a stronger or weaker population by keeping weaker species alive? In the Netherlands, the matter often seems predominantly emotional. While scientists plead for a limited amount of rehabilitation, whereby in any case no sick seals should be allowed to be removed from protected nature areas, there is a strong lobby to help all seals in need, no matter where they come from. Opponents of rehabilitation say that aid is contrary to efforts in preserving an independent and natural seal population in the wadden region. Supporters say that the Wadden Sea has not been a natural area for years now, therefore rehabilitation is not an infringement in the character of the system. In addition, they believe that rehabilitation is necessary in order to increase our understanding of the seals and the ecosystem. When in 2003 the Dutch minister Veerman tried to limit rehabilitation, the criticism was so strong that he relaxed his directives to the point that nothing changed. Rehabilitation still takes place. Seal hunt in the wadden region Seals used to be hunted intensely in the North Sea region. They were considered harmful animals. They damaged fishing nets and pinched the fish from under the fishermen's noses. Hunters were given premiums for shooting seals. In order to receive the premium, they had to hand in the right flipper to the Town Hall where it was registered. Based upon this data, it is possible to make an approximate calculation as to how many animals there must have been in 1900, when the premiums were first offered. The estimate for 1900 are between 6000 and 14,000 animals in the Dutch section of the Wadden Sea. In 1950, around 3000 seals still lived in the Dutch section of the Wadden Sea, an amount far below that in 1900. This was due to hunting. Beginning in the early 1950s, the demand for seal fur increase and practically all young seals were killed every year, leading to an accelerated decline in the number of animals in the Wadden Sea and delta region. A general hunting ban on seals in the Netherlands went into effect in 1962. At that point, there were approximately 1100 seals left in the Dutch section of the Wadden Sea. The population slowly increased after the ban went into effect. A hunting ban in Denmark and Germany was not established until 1975. After a slow begin, the population eventually recovered well from the enormous hunting pressure in the whole Wadden Sea. In fact, it recovered so well that at the beginning of 1999, the chairman of the Dutch Fisheries Union predicted that due to the large growth in the seal population, it may be necessary to shoot seals again in the future. Aand at the end of 2003, the Bird Society on Terschelling requested that the State Forestry maintain respect for island traditions. Hunting seals was one of the examples given. Seal hunt in the North Pole region Adult harp and hooded seals are hunted in Norwary. Hunting young harp seals in the northern Arctic Sea has been allowed again since the 1990s. They gave as reason that the seals caused a decrease in the fish stock. However according to seal experts, killing a relatively small number of young animals will have no regulating effect. Many more would have to be killed to see any change. The real reason for killing particularly young animals is that young harp seal fur yields more than from an adult. There is a blooming market for seal fur, especially in Asia. Because not enough hunting is being done in Norway to fill the quota, tourists are being allowed to participate if they have a hunting permit. There are too few hunters and it is difficult to see the seal heads when the wind blows too hard. Hunting season is from March to 15 April and 2100 animals are allowed to be killed. Hunting harp seals and hooded seal in Canada was reduced after actions from Greenpeace and other organizations between 1976 and 1983. Importing furs from the young seals was forbidden in Europe and the USA, whereby the fur market crashed and the worth of the seals was almost nothing. In the following period, between 1983 and 1995, 'only' an average of 52,000 seals were killed. However, when the cod fisheries collapsed in Canada in the early 1990s, certain groups of people blamed it on the seals. The renewed public acceptation of seal hunt and economic factors have led to major increase in the commercial hunt. The Canadian government finds hunting seals justifiable now because the population of harped seals is now 5.8 million animals, twice as much as in the 1970s. In 2006, the Canadian government permitted the hunt of 325,000 young seals. In 2007, the government decided that the number of young seals that could be hunted must decline by 65,000. The reason was because the ice was too thin due to the uncommonly high temperatures. Young seals that are still unable to swim sink through the ice and drown. Most of the seals that are hunted are 'beaters', harp seals between three weeks and one year old. Hunting new-born seals with a white coat has been banned since 1987. Not only the fur is used; the fatty layer is used for making oil. During the hunt of harp and hooded seals in Canada, the hunters perform cruelties on the seals at a large scale, as has been shown from video recordings in the early 21st century. In 2001, 260 violations of the Canadian law was filmed, including live skinning of seals; according to estimates, live skinning of caught seals occurs around 40% of the time. The hunters claim that 90% of the seals are shot and not beaten. Furthermore, they feel that their manner of working can be compared to the manner in which many millions of chickens, pigs, cows and other tame animals are slaughtered. Lobbyists in the field are given a very hard time by the Canadian government and the hunters. A Dutch Parliament member went to Canada in 2005 to see the seal hunt with his own eyes and was chased by a hunter with a knife. Seals younger than two weeks old are not allowed to be hunted in Canada. After this age, they loose their highly desired white coats. The European Community forbids importing seal fur from the Canadian harp seal. A majority of the Dutch Parliament was in favour of banning the import any kind of seal fur in April 1999. Weblinks For more information about the Canadian seal hunting, see the website: Information about seals in general The Seal Treaty: Seal Sanctuary Ecomare: Seal crèche Pieterburen (Dutch): Seal station Friedrichskoog (German): Sea station in Norden-Norddeich (German): Stand-by sanctuary Fiskeri- og Süfartsmuseet Esbjerg: Opinion about the future of seal care (Dutch):
|
Every day, the North Sea is treated to disposed wastes, originating from agriculture, industry and human communities. These materials find their way to the sea via rivers which mouth in the North Sea. Other waste materials come from 
