Aarhus University Seal / Aarhus Universitets segl

How to minimize the conflict ?

Investigations of harbour seals in Limfjorden and Karup Å,

and their impact on the Karup Å trout stock

Seals and anglers


The harbour seal is a protected species in Denmark, but listed in the EU Habitats Directive annexes II and V. This means that you can apply for a permit from the Danish Nature Agency to regulate the seals if they pose a threat to trout strains and fisheries. If, on the other hand, it is possible to keep them away with non-lethal methods, this can be used with fewer considerations and precautions than by regulation where the seals are being shot.

The harbour seals in Limfjorden consists of two genetic straits: the central part of the fjord is inhabited by seals from the original Limfjord population, while in the western part, a mixture of seals from this stock and seals from the Wadden Sea occur. The populations of harbour seals in Limfjorden and the South Western part of the Baltic are smaller than other populations and more vulnerable to changes in the population, as they only consists of 1500 genetically unique individuals. In 2018, regulatory permits were issued and at least 6 harbour seals were shot in Skive Fjord and Karup Å; 5 seals in the stream and 1 in Skive Fjord outside the harbour, while in 2017, 2 seals were shot in Skive Fjord, and 1 single seal in 2010 inside Karup Å. 

If it is possible to keep the seals away from trout and fisheries in the streams by means of non-lethal methods, it would help protecting the genetically unique population and make it easier to administer.

Here we test two different remedial measures, seal scarers and an electric field of pulsating direct current.


Seal scarer

The use of seal scarers as a mitigation device is investigated. Seal scarers have been used to create an acoustic barrier in streams in Scotland, which reduced the occurrences of seals further up the stream by 50%. In a similar project in Canada it was not possible to prove a significant effect. Before testing this method in Karup Å, it is important to consider the possible effect of a seal scarer on another protected mammal in the stream, the otter. Seal scarer sounds will be tested on otters in Aqua Silkeborg. Should the effect on the otters be deemed non-significant, the acoustic barrier will be tested in Karup Å.

Electric field

The use of a field of pulsating direct electrical current as a mitigation device is investigated. The electrical field creates a barrier that the seals do not like to cross. There is no actual electrocution of the animals, but the electricity disturbs the seals’ receptors in the whiskers, making them want to move away from the source. The method has successfully been used to keep harbour seals away from salmon nets in the Pacific. Before testing this method in Karup Å, it is important to consider the possible effect on the fish that need to be able to swim freely in and out of the stream to spawn and migrate, but also the effect on the otter. This will be tested in aquariums for trout and other fish species, and for the otters in Aqua Silkeborg. Should the effect on the otters be non-significant, the electrical barrier will be tested in Karup Å. 


Otter from AQUA Silkeborg by Emilie Nicoline Stepien

Otter (Lutra lutra)

 

The otter is adapted to life in the water, and its primary prey consists of fish. It is therefore important to investigate the effects of both seal scarers and electric fields on the well-being of the otter before it can be tested on seals. In that way its possible to avoid scaring protected otters away from their habitats.

Trout (Salmo trutta trutta)

 

It is important that the non-lethal methods used to keep the seals out does not affect the behaviour and migration of the trout. It is therefore a necessary to test the effect of the electrical fields’ impact on the trout before testing it on seals.