Large eyes, a woolly white coat and a birth weight between 10 and 20 kilos. They look cute, but make no mistake, says Erik Jansen, ecologist at Natuurmonumenten on Schiermonnikoog. In no time, the gray seals grow into enormous animals.
When they drink milk from their mother, the puppies gain about two kilos a day. “The males can grow up to three meters long and weigh over 300 kilos,” says Jansen.
Not surprising when you consider that an adult gray seal eats an average of 5.7 kilos of fish per day. Jansen: “The gray seal with its powerful jaws and sharp teeth is one of the top predators of the Wadden Sea.”
Before that happens, the young depend for about the first four weeks of their life on their mother, who gives birth just after spring tide, the period when the difference between high and low tide is greatest.
She does this in a carefully chosen location, says ecologist Jansen. “On the highest part of a mud flat. A puppy cannot swim right away, so it is important that it is born in a place that cannot run under water. ”
Moreover, a quiet place is chosen where no people come, because (young) gray seals are very sensitive to disturbance. “That is why they are not born on Vlieland, for example,” says Jansen.
The harbor seal gives birth in the summer, the gray seal gives birth in the winter. According to Jansen, it seems that they come into the world earlier and earlier in the winter. “Previously most of them came around Christmas, nowadays the first puppies are born at the end of November.”
Exactly how that is, is not entirely clear, according to the ecologist. Climate change could be a cause. The influx of British seals that have a different mating time and a large proportion of older seals that give birth earlier in the winter are also obvious explanations.
A female gives birth to one young at a time after carrying it for a total of 11.5 months. However, because the embryo does not develop until three months, the actual gestation period is slightly shorter.
The newborn puppy is suckled every five hours. “After about three weeks, the young are left to their own devices. Many puppies don’t survive without their mother, but luckily it usually goes well. They can use their fat reserves for about a week before they start looking for food themselves. ”
Less than a month after the birth of the seals, the males arrive on land. They flap their fins to attract the attention of the females and to scare each other.
Then they fight each other to determine which one is allowed to mate with all the females. “That is not exactly easy,” says Jansen. “After the fight, the” king “remains and the other males drip off. The females are fertilized again. ”
According to Jansen, the mammals are very mobile. “They easily swim all the way to England to go fishing. The common seal usually stays close to the Wadden Sea. ”
Gray seals in the Netherlands are doing well. The number in the Wadden Sea is increasing. Last spring, Wageningen University counted 5,687, twenty percent more than the year before. In the international Wadden Sea they counted 7649; 17 percent more.
It is still being investigated whether this is due to the corona crisis. It is quite possible that the gray seal had little human disturbance due to lockdowns.
Gray seals live not only in our Wadden Sea, but also along the coasts of the North Atlantic Ocean. The adults can be spotted in the Baltic Sea, Iceland, the Faroe Islands, Norway to Great Britain and northeast Canada. Almost all gray seals (95 percent) in Europe live in the North Sea around the Scottish Islands and along the British coast.
The males of the gray seal can grow up to three meters and weigh 350 kilograms. Females grow to a maximum of two meters and weigh 200 pounds. The seals are born with a white coat, but later turn gray with black spots. The females are usually lighter in color. They eat a lot of fish and shellfish and sometimes a bird. The gray seal can live up to 50 years.
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