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Seal monitoring

The two seal species – harbour seal and grey seal – are flagship species in the Wadden Sea National Park. In early summer the pupping season and moult of harbour seals take place on sand banks in the inner Wadden Sea. In winter they are found on sand banks closer to the edge of the National Park, as they now increasingly hunt in the open North Sea. The pupping season of grey seals is in winter and in recent years their population has been growing steadily.

Since the foundation of the Wadden Sea National Park the seal population has regularly been monitored by aerial surveys. Since 1994 this effort is conducted in close coordination between the adjoining Wadden Sea National Parks and countries (Germany, the Netherlands and Denmark) within the framework of the trilateral monitoring and assessment programme (TMAP). The seals are protected by a seal treaty that has been ratified by the trilateral states and is binding under international law. Moreover, this monitoring effort is conducted to meet the requirements of the EU-FFH guideline.

BioConsult SH carries out the aerial monitoring surveys in the Schleswig-Holstein Wadden Sea on behalf of the Landesbetrieb für Küstenschutz, Nationalpark und Meeresschutz (LKN-Tönning). After the first approval period from 2016 to 2020, further flights have been commissioned until April 2024. With five flights each year, both seal species are to be recorded. Flights to assess grey seal numbers take place in December (pupping season) and April (moulting season), while flights to record the harbour seal are conducted in June (pupping season) and August (moulting season).

All dates are intended to occur as synchronously as possible in the Wadden Sea areas and are therefore coordinated trilaterally. The flights should yield estimates for the entire population and will also take into account the recording of pup production for each year.

Results 2021 - Harbour seal monitoring

To determine the annual population of harbour seals in the international Wadden Sea, the number of seals recorded in August is considered. On August 16, 2021, a total of 8,849 harbour seals were counted in the Schleswig-Holstein Wadden Sea.

During the pupping season in June, harbour seal numbers increase in Schleswig-Holstein: on June 28, 2021, 13,908 adults and pups were counted. Due to the natural mortality of juveniles and migration of harbour seals out of the Schleswig-Holstein Wadden Sea, this number decreases until the time of moulting in August.

For 12 years, the August population has been stable, fluctuating around a mean value very close to the 2021 value.

The proportion of juveniles increased up to a maximum of 36% during the three flights in June 2021. The overall juvenile proportion has increased with annual fluctuations since the early 1990s.


During aerial surveys, all seal haul-out sites in the Schleswig-Holstein Wadden Sea are covered at low tide capturing digital photographs. The exact number of seals in these photographs is determined subsequently. In order to get a comprehensive picture of the seal population, surveys are conducted during the breeding season in June as well as during the annual moult in August.

grey seals

This picture shows seals of different ages. During the counting process the individuals are being marked differentially (males (here grey seals) = red dots; females (here grey seals) = blue dots; young (here harbour seal) = yellow dots). (The picture was taken on 15.04.2016. Click on picture to enlarge.)

grey seals A group of grey seals can be seen in this picture. A multitude of pictures is being taken during each aerial survey. The red line in this one indicates that the picture overlaps with another. Grey seals to the left of the line are being ignored in this image. (The picture was taken on 06.12.2016. Click on picture to enlarge.)

harbour seals

In this picture a group of harbour seals is shown on a sandbank with adults (red dots) and this year’s young (yellow dots). (The picture was taken on 15.06.2016. Click on picture to enlarge.)

harbour seals

Here adult seals (red dots) can be seen with this year’s young (yellow dots) on a sand bank. On either side of the image resting groups of Common eider ducks can be seen. (The picture was taken on 15.06.2016. Click on picture to enlarge.)


Thomas Grünkorn

Thomas Grünkorn