Aarhus University Seal / Aarhus Universitets segl

Habour seals and human interactions in Danish waters

Andersen, S.M. 2011. Harbour seals and human interactions in Danish waters. PhD thesis. Institute of Biology, University of Southern Denmark and Department of Bioscience, Aarhus University, Denmark. 130 pp. www2.dmu.dk/pub/SIA_phd_web.pdf


Since the protection of harbour seals in Denmark in 1977 several seal reserves have been established. In the intervening 30 years the Danish harbour seal population has increased from around 2000 to approximately 16000 individuals in 2010. Paralleling this population increase is an increase in human activity in the marine environment, both in terms of commercial and recreational use. Hence, the potential rise in number of interactions between harbour seals and humans demands a thorough evaluation of current management and its data basis.

Specifically, in order to manage the Danish harbour seals properly more detailed information on the current abundance and reproduction, as well as detailed information on harbour seal movements, and the importance of the interactions between harbour seals and human activities, such as fisheries and disturbance activities is needed.

The six papers included in the present PhD thesis starts out by providing an overview of the status of the Danish harbour seal populations (Paper I), where after examinations of management-related issues are addressed: the harbour seal - cormorant - fishery interactions in Limfjord (Paper II), the effects of constructional activity from an off shore wind farm on harbour seal haul-out numbers in the Rødsand seal reserve (Paper III), the effectiveness of current regulations in the Anholt seal reserve to protect harbour seals from disturbances (Paper IV and V), and the seasonal movements of harbour seal in Kattegat (Paper VI).

Of the few fish species overlapping between harbour seal diet and the fishery in Limfjord, only Atlantic herring was taken by harbour seals in sizes larger than the minimum sizes of the fishery. Hence, direct competition between harbour seals and the fishery did not prevail. Harbour seals however, competed strongly with cormorants, except during spring when harbour seals switched to Atlantic herring. Constructional activities in the Rødsand area apparently had no negatively impact on harbour seal haul-out numbers, though a temporary displacement was observed during the breeding season. Conversely, harbour seals exhibited a strong response towards disturbances by pedestrians and boats at their haulout site in the Anholt seal reserve. The response varied with disturber type and season, and harbour seals exhibited a high tolerance towards disturbing activities during the breeding season. This tolerance did, however, not exist before or after the breeding period, and therefore do not imply habituation.

Based on these findings, several suggestions to improve the current management of the Danish harbour seals are given.