The CWSS counted 10,044 seal pups in the entire Wadden Sea in June 2025. This corresponds to an increase of 22 per cent compared to the previous year. According to the birth figures, the population is therefore at a historic high.
A different picture emerges when counting the total seal population. A total of 23,954 animals were recorded, an increase of around one per cent compared to 2024. While the number of births has therefore risen sharply in historical terms, only moderate growth was observed in the overall population. In Denmark (-20%) and Schleswig Holtstein (-8%), the population of animals has even declined. The overall number of harbour seals is therefore lower than the birth figures suggest. Counts were conducted throughout the Wadden Sea from Denmark to the German coast and the Netherlands. Heligoland was added as a separate location. The animals were counted from the air at low tide when they were lying on the dry sandbanks.
Seal population under pressure
According to the CWSS report, the combination of high numbers of pups and a stable overall population indicates increased mortality in the seals' early life phase. As a result, many animals often do not even reach the age at which they are included in the regular population counts.
According to the CWSS report, there are various factors influencing the mortality rate of young harbour seals: climatic changes and fluctuating fish stocks mean that they spend more time in the water overall and have to expend more energy searching for food. At the same time, harbour seals are competing with harbour porpoises and grey seals for the remaining fish stocks. Grey seals not only act as competitors, but occasionally even hunt smaller seals.
Another driver of development is the influence of humans. Offshore wind farms, the use of trawl nets and heavy shipping traffic are permanently changing marine habitats. It could therefore become even more difficult for young harbour seals in particular to adapt to the new environmental conditions in the future.
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Regional differences
In Denmark, both the population and the birth rate of the harbour seal population have declined. According to the CWSS report, the number of pups here fell to 727 animals, while the total population also declined to 1,721 animals (-20%). The opposite trend was seen in the Netherlands. Here, the number of puppies rose to 2,809 animals after a weak previous year. This corresponds to an increase of 44 per cent. The total population increased by ten per cent.
In Germany, on the other hand, the picture was mixed. Schleswig-Holstein recorded a significant increase in harbour seal births, but at the same time a decline in the population. In Lower Saxony, both the number of pups and the total population increased slightly. Only two pups and around 100 animals were counted on Heligoland. Grey seals are dominant there.
Uncertainties in the extrapolation
The authors of the report estimate the total population of the Wadden Sea at around 35,200 seals. This estimate is based on a study from 1998, when they assumed that around 32 per cent of the animals are in the water in summer and therefore cannot be counted.
The authors of the current CWSS report point out that this factor could be inaccurate under current ecological conditions. For example, if harbour seals were to hunt longer at sea due to changes in feeding conditions, the proportion of animals that are not visible would increase. In this case, the beach count would indicate a greater decline than is actually the case. The report is therefore expressly in favour of reviewing and updating these assumptions.
David Ingelfinger
Volontär
