Behavioural responses of harbour seals to human-induced disturbances

In Denmark, harbour seals, Phoca vitulina, were first protected in 1977, and since then a number of seal reserves have been established in Danish waters. The effectiveness of these reserves to prevent human-induced disturbances to the seal population have, however, not been evaluated. To evaluate this, experimental disturbances were conducted in one of the most important seal reserves in Denmark (Anholt seal reserve). Specifically, the behavioural responses (alert distance, flight initiation distance, flee distances and flight duration) of harbour seals to approaching pedestrians and boats were studied. The project was conducted during three periods related to the breeding cycle of harbour seals. In all periods, harbour seals were alerted by boats at significantly greater distances compared with pedestrians (560-850m and 200-425m, respectively). Similar differences in the flight initiation distances were observed, 510-830m for boats and 165-260m for pedestrians. In most cases seals were alerted and began to flee when the approaching boat was outside the reserve, whereas seals did not respond to approaching pedestrians until after they had entered the reserve. Harbour seals exhibited weaker and shorter-lasting responses during the breeding season. They were more reluctant to flee and returned to the haul-out site immediately after being disturbed, in some cases even during the disturbance. This seasonal tolerance is most likely attributed to a trade-off between fleeing and nursing during the breeding season, and hence not an indication of habituation. Based on the results of this study it is suggested that the reserve boundaries on land be placed at least 425m from the haul-out area and the boundary at sea should extend to at least 850m from the haul-out area in order to secure adequate year-round protection from disturbances. Copyright (C) 2011 John Wiley & Sons, Ltd.