Wild boar population growth and expansion : implications for biodiversity, food safety, and animal health in Norway

Sammanfattning

Introduction: In Norway, wild boar is defined as an alien species and is considered by the Norwegian Biodiversity Information Centre (Artsdatabanken) to constitute a high ecological risk. Wild boar is, however, regarded as native in Sweden, and the population there has been rapidly expanding since the 1970s, resulting in influx of animals (about 1000 individuals today) to Norway along the border, particularly in Østfold county.

The establishment of wild boar in Norway has prompted the need for a scientific assessment of the potential for further spread and the environmental- and health risks associated with the species in Norway. The Norwegian Environment Agency and the Norwegian Food Safety Authority appointed a joint request for such an assessment to the Norwegian Scientific Committee for Food and Environment (VKM).

Method: VKM established a working group consisting of experts from Norway and Sweden, representing different fields of expertise including human-, and animal health, epidemiology and ecology to assess the potential impact from further spread and establishment of wild boar in Norway.

The working group has assessed relevant literature and used available data on wild boar occurrences and climate from abroad to model the potential distribution and population densities in Norway, both under current climate conditions and under future climatic scenarios.

The assessment of food safety and animal health considered the impact on food safety and animal health based on the assumption that wild boar is established in Norway, in significant numbers. The evaluation involved all relevant hazards with respect to animal-, and human health.

Results: Norway is currently in a similar situation to Sweden in the early 1980s, with a small population of wild boars mostly confined to one area. Unless drastic measures are implemented to control the population growth and expansion, the population will most likely double every three years, and continue to spread throughout lowland areas along the coast all the way up to Trøndelag.

Our estimates show that, based on climatic factors alone, the total population size could be 220.000 animals under current climatic conditions, which is similar to the present population size in Sweden. However, taking topography and habitat into account, a more realistic maximal carrying capacity is around 40.000 animals, spread out over 70.000km2 .

Under the prediction that temperatures will increase in the next 50 years, we find that there is a potential for increased wild boar population density, due to higher wither-survival rates, and that new areas will become inhabitable.

The ecological impact of wild boar relates to rooting and predation. Predation and herbivory might be detrimental to endangered species, while rooting might alter the structure and dynamics in various plant communities. Positive effects have been shown for early succession ephemeral plants, including alien species, while negative effects are more pronounced for perennials in more stable communities. The available literature does show both positive, negative and no effects of wild boar rooting, depending on the system under study. Wild boar will also have negative effects on agriculture through both rooting of pastures and meadows and seed predation on crops.

Discussion: Based on the experiences from Sweden and other relevant countries, it is obvious that the presence, spreading and establishment of wild boar is tightly linked to human interference. The species natural dispersal is about 2,5 km per year, but translocation of animals for hunting purposes have been widespread in other countries, leading to much longer dispersal distances and establishment of new sub-populations. Also, supplemental feeding have been shown to have a profound effect on the population growth and potential wild boar density. To what degree these measures are practiced in Norway will be decisive for how the distribution and local population densities will develop.

Based on a number of different criteria (e.g., presence in neighbouring countries and zoonotic potential) and evaluation of exposure pathways, we have identified seven novel agents likely to be introduced to Norwegian pig populations from wild boar. These can cause serious diseases like Classical-, and African Swine Fever and Foot and Mouth Disease. It is also expected that the prevalence of Salmonella ssp., Trichinella ssp. and Taxoplasma gondii will increase, which can result in higher transmittance to humans.

Conclusion: Unless drastic measures (i.e., culling) and ban on feeding are enforced within the next few years, the wild boar population will most probably grow significantly and spread to new areas in Norway, especially along the coast. Expected future climate conditions will be more suitable for wild boar, but the main factor influencing the population development will be human activity in terms of translocation and supplemental feeding.

Wild boar might have severe impacts on both agriculture and wild ecosystems. However, only a limited number of long-term studies exist, making it difficult to predict what will happen in Norway. There is also a lock of studies assessing the effects of contrasting wild boar densities, an aspect that is highly relevant for assessing the potential impact.

Biosecurity remains the most effective way to prevent disease transmission between wild boars and domestic pigs. The probability of direct transmission of African Swine Fever from wild boar to farmed pigs is very dependent on the biosecurity conditions of farmed pigs, as well as on density of wild boar. The probability of direct transmission from wild boar to farmed pigs is high if farmed pigs are kept in outdoor facilities, given that the disease enters the population through Sweden.

Nyckelord

VKM; risk assessment; Norwegian Scientific Committee for Food and Environment; Norwegian Food Safety Authority; Norwegian Environment Agency; wild boar; population; growth; expansion

Publicerad i

Report from the Norwegian Scientific Committee for Food and Environment (VKM)
2018, nummer: 2018:14ISBN: 978-82-8259-311-3Utgivare: Norwegian Scientific Committee for Food and Environment

SLU författare

• Thurfjell, Henrik

  • SLU Artdatabanken, Sveriges lantbruksuniversitet
    

UKÄ forskningsämne

Ekologi
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https://res.slu.se/id/publ/131469