Seals 2002 Common Seals in the Wadden Sea in 2002 Common Wadden Sea Secretariat, Wilhelmshaven November 2002   Common seals in the Wadden Sea areas of the Netherlands, Lower Saxony, Schleswig-Holstein and Denmark are monitored through trilaterally coordinated aerial surveys. The flights are scheduled during the seal whelping and moulting seasons (i.e. June/early July and August, respectively), when the highest numbers of hauling out seals can be registered. Annual maximum counts from the four sub-areas have been added to give a total number for the Wadden Sea. In 2002, the maximum counts revealed an all time high number of 20,975 registered seals in the whelping season. Among these, 4,735 were newborns. Clearly, the population continued yet to increase, as it has done since 1989 (see Fig.).The average rate of increase over the last five years (1997 – 2002) was 10% p.a. Note that the 2002 count results for the Danish Wadden Sea were put together in another way than before. From 2002 onwards the result will strictly refer to the area under Danish administration, the southern border of which runs through the Sylt-Rømø-Bight. In earlier years, quoted numbers included those animals encountered in the German part of the Sylt-Rømø-Bight. This was changed now so that the sum of the count results quoted for the political sub-areas equals the number of seals given for the entire Wadden Sea. Like in 1988, the growth of the Wadden Sea seal population was interrupted by an outbreak of the pdv disease in 2002. The population size this year was roughly twice that of 1988. Although the epidemic has not yet completely come to an end, it seems that the number of seals found dead in the entire Wadden Sea area is not twice as high as found in 1988 (see contribution by Reineking in this issue). Given the larger size of the population now, it is tempting to conclude that the percentage of the mortality is smaller this time. This impression may be misleading, because the number of seals washed ashore partly depends on weather conditions, particularly wind direction. In 2002, there were long periods of off-shore winds. It is premature to conclude about the actual mortality rate. The percentage loss of seals of the population will become more evident in the 2003 count season. The 2002 maximum count results were apparently not affected by the epizootic, since the maximum count for the whole Wadden Sea is usually obtained in late June. By that time this year, there had only been a few pdv victims in the Netherlands. The 2002 mass mortality will likely be followed by an another phase of increase. While the characteristic growth rate of this population is known to be 10 – 13% p. a., the exact development of the growth rate is hard to be foreseen, because it depends to some extent on the age distribution of the seals. In case of an age distribution of the surviving seals, abnormal annual changes between 0 and 20% of the growth rate may occur for limited periods. Trilateral Seal Expert Group: DK:      Svend Tougaard, Fiskeri-og Søfartmuseet, Esbjerg SH:      Ursula Siebert, Kai F. Abt, FTZ Büsum der Universität Kiel LS:       Michael Stede, LAVES Cuxhaven NL:       Peter J.H. Reijnders, Sophie M.J.M.Brasseur, Alterra – Marine and Coastal Zone Research, Texel  Figure 1: Number of Counted Seals in the Wadden Sea since 1975   Home | Trilateral Cooperation | News/Service | Management | Monitoring | Interregional Cooperation