The harbour seal
Two species of wild predators live along the Dutch coast: the harbour (or common) seal and the grey seal. Harbour seals are the most numerous in the wadden region. During low tide, they like to bask in the sun upon the sandbanks. During the summer, it is here where the young are born and nursed. They hunt for fish in the Wadden Sea and North Sea, covering large distances at times. Prior to 1980, the seal was first threatened by hunting and later on by pollution. Since then, the seal population has grown immensely, although two serious virus epidemics have prevailed.
Male harbour seals can reach a length of 1.80 meters and a weight of 130 kilograms. Females grow to 1.70 meters and a weight of 105 kilograms. In captivity, they can reach the age of forty while in nature they do not get older than twenty to thirty years. The harbour seal eats four to eight kilograms of fish per day.
The development of the Dutch population
In 2008, 5972 harbour seals were counted in the Dutch wadden region. Scientists assume that around 30% of the seals are underwater during a count, bringing the total population to an estimated 8500 animals.
The history of the population of harbour seals in the Dutch section of the Wadden Sea has had peaks and drops, caused by hunting, pollution and disease. Around 1950, approximately 3000 harbour seals still lived in the Wadden Sea. Because in those days one believed that the seal was a serious competitor for the fishermen, 500 to 600 animals were shot every year. Furthermore, furs from young seals came into fashion around this time. Because too many young animals were being killed, the seal population continually diminished. By the end of the 1950s, there were only approximately 1000 animals still around.
In 1962, hunting seals in the Netherlands was forbidden. As can be seen in the graph, the population grew up till 1965. Then another decline occurred; this time the cause was pollution in the seawater. Especially PCBs appeared to have a negative influence on the reproduction of the seals. The numbers continued to diminish halfway through the 1970s to an absolute low of approximately 500 animals. Slowly but surely, the population recovered, reaching approximately 1000 specimen in 1987. The growth was due to a ban on the use of PCBs, a ban on hunting seals in Germany an Denmark in 1975 and the work of the two Dutch rehabilitation centres, Ecomare and the seal crèche in Pieterburen, which began to bare fruit. As of 1988, the situation was determined by two epidemics. The population recovered quickly after both epidemics. In the summer of 2003, directly after the epidemic of 2002, around 2350 harbour seals were counted on Dutch sandbanks and tidal flats in the wadden region; five years later, it had almost doubled in size.
Distribution of harbour seals
Harbour seals are considered typical coastal inhabitants. One rarely spots a seal in open sea. Nevertheless, experiments done in 1997 where seals were provided with transmitters showed that seals often swim more than 100 km into the North Sea. The reason why seals are probably not often seen in open sea is because they stay mostly under water. The harbour seal is found along almost all coasts of the northern Atlantic and Pacific Oceans, including their bordering seas. Their preferences are tidal areas and river mouths, where isolated sandbanks or stones are exposed during low tide.
Other subjects:
Life as a harbour seal
Seal conservation areas
Weblinks
http://www.arkive.org/species/ARK/mammals/Phoca_vitulina/more_info.html#Facts
Names:
Dut: Gewone zeehond
Eng: Harbour seal (common seal, sand seal)
Fren: le veau marin
Ger: Gemeiner Seehund
Lat: Phoca vitulina
Dan: Spættede sæl
Nor: Steinkobbe
