The seal counts of the entire Wadden Sea are synchronised to the degree possible between the three Wadden Sea countries, Denmark, Germany and the Netherlands, in order to obtain a single estimate for the number of harbour seals and pups in the entire Wadden Sea. Seals are counted when hauling out on land and counts are scheduled to be carried out when low tide occurs around midday. The variation in the number of seals hauling out from year to year and over several years may be affected by different weather conditions, disturbance, distance to food patches, or a change in the age and sex composition of the population (Härkönen et al. 1999). Also, the timing of birth has been shown to change over time, potentially affecting the percentage of pups counted at the same time of year over a long period (Reijnders et al. 2010). It is unclear if and how this shift might also affect the moult counts. It is of importance to understand if changes in timing of pupping and moult have occurred due to changes in age composition in the population, climate change or other environmental factors. The timing of the surveys depends on this. Therefore, studies on these topics should be initiated as soon as possible. These studies could include additional coordinated surveys in some particular years or detailed studies on the number of seals on land on selected haul out sites.