Directional breeding migration of harbour seals in the Wadden Sea
Brasseur, S.M.J.M.; Reijnders, P.J.H.; Kirkwood, R.; Aarts, G. (2017). Directional breeding migration of harbour seals in the Wadden Sea, in: Brasseur, S.M.J.M. Seals in motion. How movements drive population development of harbour seals and grey seals in the North Sea. pp. 54-71
In: Brasseur, S.M.J.M. (2017). Seals in motion. How movements drive population development of harbour seals and grey seals in the North Sea. PhD Thesis. Wageningen University: Wageningen. ISBN 978-94-6343-612-0. 176 pp. https://dx.doi.org/10.18174/418009
Migration plays a central role in the spatial dynamics of many mobile species, but it has not been identified in the harbour seal (Phoca vitulina), which is generally considered a non-migratory species. However, in the Wadden Sea, extending from the Netherlands to Denmark, there is a regional misbalance between harbour seal pup production and resident population size. This led to the hypothesis that an annual breeding migration might occur. Harbour seals in the Netherlands were tracked with GPS data-loggers. The movement data were analysed to study whether harbour seals in the Wadden Sea migrate annually between the feeding and breeding areas. We demonstrate that prior to the breeding season a large proportion (30%) of females from Dutch waters where pup production is low relative to the numbers counted during the moult season; migrate towards Germany in the east, where pup production is higher. Also, the majority of animals tracked after the breeding season, including 78% of adult females, moved in the opposite direction, to the west, suggesting a return migration.
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