Haul-out behaviour of the Norwegian harbour seal during summer

Abstract

Background: the haul-out behaviour of the Norwegian harbour, seals had previously not been studied throughly. Methods: the intent was to examine the haul-out behaviour in relation to three factors: (1) the diel light cycle, (2) the tidal cycle and (3) the interaction between these two cycles. Observations were therefore made on days with low tide around noon, and later repeated on days with high tide around noon. The number of hauled-out seals was counted every hour, day and night. Three places were selected on the basis of their differing characteristics in diel light and tidal variation during summer. Results: the diel light cycle, the tidal cycle, and the interaction between the two cycles, all showed a significant relation with the haul-out behaviour both at Froan and in Kongsfjord. At Hvaler, the haulout pattern was very inconsistent, with large fluctuations from day to day. Conclusions: the higher numbers of hauled-out seals in the daytime, especially in Froan but to a certain degree also in Kongsfjord, may indicate that most seals feed at night. Similarly, the higher numbers hauled out at low tide, especially in Kongsfjord but also in Froan, may indicate that most seals feed around high tides. At Hvaler, the seals may be less at ease by the great deal of commercial and recreational boat traffic.