Harbour Seal Numbers in the Wadden Sea and on Helgoland in 2022
Expert Group Marine Mammals
To obtain an estimate of the number of harbour seals and pups hauled out in the entire Wadden Sea area (including Helgoland), counts are synchronized between the three Wadden Sea countries, Denmark, Germany and the Netherlands.
Harbour seals are counted when hauling out on land and counts are scheduled to be carried out when low tide occurs around midday. The five counts are scheduled around five dates to describe pup production and moult numbers accurately. Three counts are aimed at pup numbers during the pupping season in June and two during the moulting season in August aim to obtain an estimate of the population size and its fluctuations.
The observed variation in the number of seals hauling out 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 each year over a long period (Reijnders et al. 2010). Though efforts are made to maximise the standardisation of the surveys with respect to weather, tides and dates, changes could influence the counts. Additional studies are needed to ascertain when the peak in birth and moult occurs.
Authors: Anders Galatius, Sophie Brasseur, Florian Carius, Armin Jeß, Kristine Meise, Julia Meyer, Jessica Schop, Ursula Siebert, Ole Stejskal, Jonas Teilmann, Charlotte B. Thøstesen
This report was published 2022-11-01.
This report should be cites as: Galatius A., Brasseur S., Carius F., Jeß A., Meise K., Meyer J., Schop J., Siebert U., Stejskal O., Teilmann J., Thøstesen C. B. (2022) Survey Results of Harbour Seals in the Wadden Sea in 2022. Common Wadden Sea Secretariat, Wilhelmshaven, Germany.