Harbour seals haul out (=come ashore) in order to rest, moult and breed. For breeding, seals use inter-tidal sandbanks within estuarine environments, e.g. Dutch Wadden Sea, because they are available only at low tide. Eems-Dollard is the only Dutch Wadden Sea core breeding area, consisting of eight major haul-out sites. During the 30-day lactation period seal females care for only one pup at a time and transfer a substantial amount of energy to their pups in form of lipid-rich milk. How do they manage? Females use both stored energy and energy from supplemental feeding, and therefore loose 32% of the body mass they had before birth. Undisturbed haul-out sites and long exposure times are essential for pup growth and survival. Thus, if females need to breed close to human activity, this could increase the risk to be exposed to anthropogenic disturbance (= caused by humans).

Aim was to get information about

? abundance of harbour seals in the Eems-Dollard (How many and where?)

? behaviour of mothers and pups (What do they do?)

? disturbance in this area (What is disturbing? How often does it happen? Effect?)

Thus, the aim of this study was the investigation of a) the haul-out pattern and abundance of harbour seals (Phoca vitulina) on inter-tidal sandbanks in a Wadden Sea estuarine environment, b) the frequency, initiation and duration of mother-pup interactions and c) the frequency and impact of anthropogenic disturbance during breeding season (May/June/July).