Aarhus University Seal / Aarhus Universitets segl

Surveillance
of seals

Since 1976, the harbour seal population has been rising. In Denmark, the grey seal went extinct in the early 1900’s; however, in the last 15 years, it has returned to Danish waters.

Surveillance by plane

Grey seals and harbour seals

Surveillance by plane photo by Casper Tybjerg

Estimates of grey seal and harbour seal populations are often conducted by plane. Through these surveys, population development can be tracked by comparing the number of counted individuals from each year. The seals are counted when resting on land. These counts take place during their molting and reproduction periods because this is when the seals are more likely to spend their time on land. Harbour seals give birth in June and molt in August, while grey seals give birth in February-March and molt in May-June.

The estimations from the reproduction periods can be used to understand the productivity of young, and thereby indicate the well-being of the species. Read more about satellite tagging of seals and telemetry.