Grey seal population in the Wadden Sea steadily growing

Since the return of the grey seal to the Wadden Sea in the mid-20th century, the population has been growing steadily. In 2018-2019, 6,538 individuals were counted in the Danish-Dutch-German Wadden Sea and Helgoland. This increase of 6 % compared to the previous year can be seen in most regions, with some variation. In Denmark a particularly high increase of 79 %, from 228 to 408 animals was observed. These numbers indicate that the locally occurring grey seals are expanding their range throughout the area of the Wadden Sea. These are the main findings of the report “Grey seal surveys in the Wadden Sea and Helgoland in 2018-2019”, published by the Trilateral Expert Group Seals (EG-Seals) of the Trilateral Wadden Sea Cooperation.

“In light of the 10th anniversary of the Wadden Sea’s designation as World Heritage site, which we celebrate this year, I take it as a special gift that we see the grey seals prosper in the Danish Wadden Sea,” says Sascha Klöpper, Deputy Executive Secretary of the Common Wadden Sea Secretariat (CWSS). “For the moment, the grey seals observed in Denmark are non-breeding animals or breeding elsewhere, but in the future a new breeding colony may settle there as well, which can already be said for the other parts of the Wadden Sea.” Since the 1970s most parts of the Wadden Sea hold a conservation status. In 1991 an agreement was set in place to protect harbour seals, holding benefits also to grey seals. In 2009 the UNESCO World Heritage Committee titled the Wadden Sea a Natural World Heritage Site.

Since 2008, the EG- Seals (former Trilateral Seal Expert Group, TSEG) organises annual trilaterally coordinated surveys to observe both adult grey seals and pups. Adult seals are counted during the moulting season, when they spend substantial time on land. Next to the steep increase noted in the Danish Wadden Sea, since 2017-2018 numbers have also grown in the Netherlands with 4,760 counted animals (+4%) and in Lower Saxony and Hamburg wit 451 adult seals (+18%). In fact it is the first year grey seals are consistently being observed in the Wadden Sea of Hamburg. In Schleswig-Holstein numbers decreased both on Helgoland by 2% (764) and in the Schleswig-Holstein Wadden Sea by 18% (155). The EG-Seals states that differences between areas may be due to several reasons, including food availability in the surrounding area, changes in haul-outs, or local disturbance.

Newborns are monitored during the pupping season in the winter months. In the 2018-2019 season, 1,684 pups were recorded in the Wadden Sea and Helgoland with an increase of 22 %. The majority of pups, 1,062 individuals, were born in the Dutch Wadden Sea – with 29% the biggest growth. On Helgoland and in Lower Saxony numbers also grew by 20% and 3% respectively (387 and 235 counted pups). In Denmark, Schleswig-Holstein and Hamburg, no pups were recorded on the selected surveying dates, although one or two pups were observed that winter season in Schleswig-Holstein.

Grey seals are the largest predators along the Wadden Sea coast and, like harbour seals, they are one of the iconic species of the region. In former times grey seals were most possibly numerous in the Wadden Sea until they disappeared most probably after excessive hunting practices. They recolonised in the second half of the 20th century, originating from UK waters. Part of the Trilateral Wadden Sea Cooperation, the Trilateral Expert Group Seals (EG-Seals) (former TSEG) coordinates the counts and harmonizes the data from across the Wadden Sea region. The most numerous seal species in the Wadden Sea, the harbour seal, is specially protected under the Agreement on the Conservation of Seals in the Wadden Sea (WSSA) concluded under the auspices of the UN Convention on the Conservation of Migratory Species of Wild Animals (CMS). Although the WSSA does not officially cover the grey seal, the species benefits from the agreement’s protection measures. CWSS acts as the secretariat of WSSA.

The full report can be downloaded here.