Aarhus University Seal / Aarhus Universitets segl

Seals in streams 

Investigations of harbour seals in Limfjorden and Karup Å,

and their impact on the Karup Å trout stock 

Seals in streams logo by Mads M. Strøbech


Emilie Nicoline Stepien
Tlf.: +45 25709791
Mail: stepien@bios.au.dk 

Harbour seals in Limfjorden


The harbour seal is a marine mammal found in most Danish waters. They occur in lakes and streams throughout most of their range, including Denmark. The abundance of harbour seals in Denmark has been steadily increasing since the last PDV (Phocine Distemper Virus) epidemic in 2002 and is now around 17.000 individuals. This general growth, however, has not been observed in the central part of Limfjorden, where the estimated abundance of harbour seals has been at a more or less constant level of 1500 individuals since 2002. Over the past ten years, conflicts with the fisheries and the anglers in particular have increased. After the anglers started to create spawning grounds and releasing mother fish, they experienced more observations of seals in the streams and lakes. Increased seal presence in streams could potentially influence stocks of salmon and trout negatively, but reported reduced catch rates could also cause difficulty in attracting members for the anglers’ associations. 

Project aim

The purpose of this project is to investigate and compare the harbour seals’ influence on the trout stock in Karup Å by investigating the diet of the seals in the area of the stream and in the stream itself. The results will also be evaluated in the context of other predators (otter, cormorant, humans) and how they influence the stock. Furthermore, the project will look into the possibilities of introducing two non-lethal mitigation methods: 1: Seal scarers, an acoustic barrier that is placed in streams and reduces the probability of seals passing through and continuing further upstream, and 2: A field of pulsating direct electrical current that also can prevent the seals from passing through and swimming upstream. The project will thereby support the management of seals in relation to trout – and salmon stocks, partly by estimating the seals’ impact on these, and partly by investigating relevant, non-lethal actions of management.

Seal track near Sundsøre Tange
Seal track near Sundsøre Tange

Wildlifetracking - follow the seal

In order to know where the seals spend most of their time and whether they do in fact enter the stream, seven animals have been tagged with a special transmitter. The data from the tags is uploaded to Wildlifetracking.dk with a new position.