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A conservation success story: 30 years of the Wadden Sea Seal Agreement – a milestone for the remarkable recovery of the Wadden Sea harbour seal population.

Friday 1st October, 2021

30 years ago, on the 1st of October 1991, the Agreement on the Conservation of Seals in the Wadden Sea (Wadden Sea Seal Agreement/WSSA)) entered into force and became the first international, legally binding agreement under the auspices of the UN Convention on the Conservation of Migratory Species of Wild Animals - established in the year 1979. The Trilateral Wadden Sea Cooperation’s aim with the agreement was to achieve and maintain a favourable conservation status for the Wadden Sea harbour seal population through close collaboration in research and monitoring and by increasing the public awareness as an integral part of this ecosystem.

The agreement became necessary due to the massive decline in harbour seal numbers in the Wadden Sea. While the harbour seal population was estimated at roughly 40.000 animals in 1900, in the 1960’s less than 10% of the population were left. As marine top predators, harbour seals use the same resources as we do, namely fish, and are viewed by some as a threat to local fisheries and were severely hunted in the first half of the 20th century. Urgent policy changes were needed to help the seal population to recover and by 1977 hunting bans were in place in all three Wadden Sea countries. While first signs of recovery were observed in the following years, pollutants such as polychlorinated biphenyl discharged from the river basins limited the seals ability to reproduce, and the outbreak of Phocine Distemper virus in 1988 decimated the population by 57%. These events further illustrated the need for increased trilateral cooperation in the management of the population and the establishment of the WSSA.

Despite a second outbreak of Phocine Distemper virus and a resulting population decline of 50% in 2002, the harbour seal population has recovered significantly since the Wadden Sea Seal Agreement came into effect. In the 2017 Quality Status Report it was stated that the population has once again reached the pre-hunting population size of roughly 40.000. The exceptional growth rate of this population has stabilised since and the population is now regarded as viable and in no immediate risk of critical decline.

For the three Wadden Sea countries the agreement has made impacts that can been seen in management changes, which have been adopted based on the results of the trilaterally agreed monitoring carried out regularly which reflects and supports the continued success of the WSSA. In Germany, several decades of intensive conservation efforts in the states of Schleswig-Holstein, Hamburg and Lower Saxony have laid the basis and thus contributed to making this Wadden Sea-wide agreement a success for species conservation in Germany: a management system has been established, and in particular pupping and moulting sites in the National Parks are under special protection. Raising public awareness for the importance of protecting the Wadden Sea as a habitat for the seals, which is supported by the local information and seal centres, is also a key component in management.

Tineke Schokker, chair of the Dutch Seal Rehabilitation Agreement Group, is satisfied with the results of the agreement so far: “In the last thirty years, we managed via the Wadden Sea Seal Agreement to reach a very healthy population of seals in the international Wadden Sea. I am proud that the recently concluded Seal Agreement in the Netherlands demonstrates and reinforces our common objective to act fully in line with this trilateral WSSA.”
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Natural disease outbreaks are likely to reduce the population size of harbour seals at regular intervals, but if the population is well managed these outbreaks are unlikely to critically threaten the conservation status of the Wadden Sea population. A variety of human activities, including pollution, shipping, fisheries, construction of wind farms, and tourism, have the potential to negatively affect the population. With the transnational monitoring programme and the regularly updated Seal Management Plan, the Trilateral Cooperation has strategies in place to assess the impact of human activities on the harbour seal population and to ensure the quality of their Wadden Sea habitat is sufficient to protect and to maintain the seal population at this level. It will also aid the recovery of the harbour seals population after naturally occurring disease outbreaks.