The import and release of Swedish mallards can harm Norwegian biodiversity and water quality


Report no: 2017: 23

Published: 15.06.2017

Key message:

The import of farmed mallards from Sweden and the subsequent release of these birds for hunting purposes may have negative consequences for Norwegian biodiversity and water quality. The health and welfare of the released birds are also of concern. The magnitude of the negative consequences is expected to increase with increasing number of birds being released.

This is the main conclusion of a recently published risk assessment by the Norwegian Scientific Committee for Food Safety (VKM). The risk assessment was assigned by the Norwegian Environment Agency and the Norwegian Food Safety Authority.


VKM highlights a range of negative consequences associated with the import and release of mallards for hunting purposes. This includes negative consequences for biodiversity and for the welfare of the released mallards. According to the Chair of the working group, Dr. Eli K. Rueness, the extent and severity of the consequences are dependent on the number of mallards being released.

There is a risk of interbreeding between released and wild mallards. In the long run, interbreeding could cause negative genetic effects, for example if the wild mallards survival skills are affected. This affect both wild mallards and other species of ducks, including red-listed species.

Furthermore, VKM concludes that there is a risk of reduced water quality in the release areas, because of an increasing amount of mallard faeces in the water. This can contribute to reduce the level of oxygen in the water and thus the water quality. The severity of the impact will increase with an increasing number of released birds as well as with increasing number of years of consecutive release in the same lake or pond.

Animal health and welfare

There is risk that the imported mallards could introduce a range of contagious diseases, such as for example bird flu (Highly Pathogenic Avian Influenza, HPAI). While the probability of this event occurring is low, there are serious consequences related to the spread of such diseases in Norway, says Rueness.

VKM concludes that there is a high risk of reduced animal welfare among the released mallards.

The mortality rate of the farmed mallards is shown to be higher than that of wild birds. The released birds die from hypothermia, malnutrition, starvation and from being taken by predators. While the high mortality rate decreases the chances of negative impacts on biodiversity, it is likely that the mallards suffer before they die, Rueness states.

Knowledge gaps

There is currently limited knowledge concerning the consequences resulting from large-scale releases of mallards. To increase knowledge, VKM suggest genetic mapping of all mallards prior to release, marking studies to study dispersal and behaviour patterns, and regular water chemistry sampling.


For several years, hand-reared mallards have been imported to Norway from Sweden. In Norway, the mallards are released for hunting purposes. The Regulation on Alien Organisms was effectuated on January 1st, 2016. Under this Regulation it is required that anyone who wants to import and release mallards for hunting purposes must have permission from the authorities. To process permit applications related to import and release of mallards, the Norwegian Environment Agency requires a scientific opinion on the negative effects this practice could have on native biodiversity.

The risk assessment was carried out by VKMs panel on Alien Organisms and Trade in Endangered species (CITES).


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