Harbour seals population thriving in the Wadden Sea

2019 has been another record year for harbour seal pups observed in the Danish-Dutch-German Wadden Sea. The number of newborns was the highest and its percentage of the total August moult count is the second highest ever recorded. The Expert Group Seals (EG-Seals) of the Trilateral Wadden Sea Cooperation estimates a total of 40,800 harbour seals in their newly published “Trilateral surveys of Harbour Seals in the Wadden Sea and Helgoland in 2019”, based on trilaterally coordinated surveys in the Danish, Dutch and German parts of the Wadden Sea World Heritage site.

“For years now we have observed a very strong and stable harbour seal population,” states Bernard Baerends, Executive Secretary of the Common Wadden Sea Secretariat (CWSS). “These are especially good news when remembering the severe disturbances in the past decades, from human activities to outbreaks of the phocine distemper virus in 1988 and 2002, as well as influenza virus in 2014, all of which caused significant losses. We can safely assume that our measures and trilateral cooperation to protect the marine mammal and its habitat are showing real impact in leading to a thriving population.”

The trilaterally coordinated aerial surveys are conducted twice a year – during moulting season, when harbour seals spend more time on land, and during pupping season. During the moult in August 2019, a total of 27,763 harbour seals were observed in the Wadden Sea and Helgoland, which is a minor increase of one percent to 2018, yet the highest count recorded since the first counts in 1975. The EG-Seals state that the result is a continuation of the stabilizing trend seen since 2012 where the average annual growth rate has been 0.4%. Looking at the regions, the harbour seal population in the Danish Wadden Sea remains the same at 2,676. In Schleswig-Holstein Wadden Sea, 8,721 seals were counted (+1% compared to 2017; no numbers for 2018 available) and 8,772 in Lower Saxony and Hamburg (+9% from 2018). In the Netherlands the count slightly decreased by 7% (7,338 individuals). On Helgoland the highest regional growth was noted with 256 seals and an increase of 33% to 2018. Shifts in regional numbers may have different reasons, such as a variation in the survey date, varying numbers of seals hauling out, weather or a migration between areas. The latter underlines the significance of trilateral counts and that harbour seals in the Wadden Sea must be regarded as one large population.

During the 2019 pupping season in June 9,683 pups were counted in the Wadden Sea, which is the highest number registered yet (+2% to 2018). Divided into regions, in Schleswig-Holstein, where in 2018 a large increase was observed, a significant decrease was detected (-19% to 2018) with 3,723 pups counted. In Denmark, 919 pups were counted (+64%). In Lower Saxony and Hamburg an increase of 26% was noted with 2,711 pups. In the Netherlands 2,330 newborns were recorded (+6%).

The percentage of pups of the total August moult count was 35%, the second highest ever recorded. The EG-Seals concludes that this trend, which has been observed since 2012, is paradoxical, as one of the signs of a population approaching carrying capacity would be a decrease in pup production or pup survival. Nevertheless, pup production has increased and in order to investigate pup survival, comprehensive data has yet to be collected.

Harbour seals, as well as grey seals, are one of the iconic species of the region. 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 harbour seal is trilaterally 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). CWSS acts as the secretariat of WSSA.

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