Seal counts 2015: Seal population resists influenza

Seal counts 2015: Seal population resists influenza

The harbour seal population in the Wadden Sea remains stable in 2015. Despite an increasing number of dead animals along the shore lines in autumnand winter 2014, caused by the appearance of the Influenza A virus, the overall population has remained largely unaffected. Coordinated counting flights in the whole Wadden sea area revealed similar harbour seal numbers as in the previous years. The Trilateral Seal Expert Group (TSEG), which is responsible for the coordination of these flights, stated that the population is very solid, the numbers decreased by less than 1% compared to 2014.

Since the last massive epizootic in 2002, which killed almost half of the population, harbour seal numbers increased constantly until 2013. The experts considered recent growth rates as a sign that the overall increase of the population has slowed down. Traditionally the seal counts are conducted during the moulting period in August, when many animals rest on haul out sites on sand banks and beaches. Consequently, last year’s influenza effects were documented for the first time in this year’s seal numbers. In Denmark and Schleswig-Holstein, which were mostly affected by the disease, 3,400 Harbour seals were found dead or severely sick. In Lower Saxony and the Netherlands only a small number of dead animals were found later in the year. Last year’s assumptions by the TSEG that the disease might not have a major impact on the overall population were finally confirmed by seal numbers in 2015. During the surveys a total of 26,435 harbour seals were counted in the Danish, Dutch and German Wadden Sea. Since a considerable number of harbour seals are in the water during the surveys, an assumption based on scientific investigations leads to a total of 38,900 animals in 2015.

The grey seal population was not directly affected by the influenza. Following a remarkable increase in 2014, the total number of grey seals in the Wadden Sea was 4,521 during the moulting period in spring. This is an increase of 5% compared to last year. The number of 829 pups indicates a further growth of the breeding population. For the first time specific grey seal counts in Denmark were conducted and the first newborn pup in the Danish Wadden Sea was documented. It seems that the grey seal population is establishing itself further in the Wadden Sea area and that the population is expanding northwards. As documented in former years, there is a major influence on the local population by visiting animals from UK waters.

For details, please also visit http://www.waddensea-secretariat.org/monitoring-tmap/topics/marine-mammals