Promotores: H.A. Udo De Haes, P.M. Brakefield
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In Dutch waters, two seal species occur namely common seals (Phoca vitulina vitulina) and grey seals (Halichoerus grypus). In the 1970s, the common seal population reached a historical low point after centuries of hunting, followed by exposure to pollution. Grey seals had already disappeared from Dutch waters in the preceding centuries, probably due to hunting. In this thesis, seals were studied over a period of four decades (1971-2013) in which the common seals have shown a recovery and the grey seals successfully recolonised Dutch waters. The research is conducted in the period 2006-2013 at the Seal Rehabilitation and Research Centre (Pieterburen) in collaboration with several universities. A multidisciplinary approach has been applied to learn more about the biology and pathology of seals and to obtain a comprehensive view on their status in Dutch waters. The patterns and trends in stranding were studied for both seal species, followed by a study of their current genetic status. Based on the analysis of stranding data, parasitic pneumonia (common seals only) and orphanage (both species) were found to be the main causes of stranding. Therefore, the occurrence of parasitic infections and the breeding biology of seals were studied in the following chapters.