Following a dramatic decline, Arctic foxes are gradually recovering in northern Europe thanks to targeted conservation efforts. But while their numbers are rising, their genetic diversity isn’t – and targeted interventions are now underway to address the risks of inbreeding.
Their snow-white winter fur – among the finest and warmest in the animal kingdom – spelled the downfall of the beautiful Arctic fox in many places. From the late 19th century onward, they were ruthlessly hunted for their coveted pelts, bringing them close to extinction in many regions. It wasn’t until the 1920s that hunting was restricted and the species gradually placed under protection. However, the populations showed little sign of recovery in the decades that followed.
Thousands of Arctic foxes also fell victim to fur hunters in Norway, Sweden and Finland. Once widespread across Fennoscandia, they were threatened with extinction after the end of the hunt – not only due to decades of overexploitation, but also as a result of indirect factors such as poisoned bait intended for wolves.
For many decades, the remaining Arctic foxes survived in small, isolated populations that were so decimated and fragmented they were barely able to recover on their own. To make matters worse, the red fox advanced further into Arctic fox territory – presumably due to climate change. There, it became not only a competitor for food but also a direct threat, occasionally preying on Arctic fox cubs.
Other reasons for the stagnating population size include the strongly fluctuating lemming populations, which are increasingly affected by climate change. Lemmings are the most important food source for Arctic foxes. If the lemming population collapses in a given year, the foxes often fail to reproduce.
The dramatic decline in the Arctic fox population has also led to a significant loss of genetic diversity. Inbreeding is becoming increasingly common within the widely separated subpopulations, which can result in smaller litters and a shortened lifespan in adult animals.
According to a recent report by the Norwegian Institute for Nature Research (NINA), only 40 to 60 adult Arctic foxes remained in Scandinavia in 2000. To prevent the species from going locally extinct, the Norwegian Environmental Protection Agency, together with NINA and other partners, launched a captive breeding program in 2005 – with great success.
Since then, hundreds of young foxes have been reared at the breeding station in Sæterfjellet near Oppdal, Norway, and released into the wild in various areas to strengthen existing subpopulations or establish new ones. In the future, animals will be selected to be as genetically unrelated as possible to the local foxes.
“We recommend prioritizing areas where the effective population size is particularly low or where inbreeding is increasing. The effective population size is a measure of how genetically robust a population is. It is influenced, among other factors, by the proportion of adult Arctic foxes that contribute with offspring and thereby pass on their genes,” explains Øystein Flagstad, geneticist at NINA and lead author of the report, in a press release from the institute.
As additional protective measures, feeding stations were established and red foxes were selectively hunted to reduce competition.
Thanks to combined conservation measures, 400 to 600 adult Arctic foxes are now roaming Fennoscandia once again. However, the report warns against overestimating this success: inbreeding remains a problem, with the well-known negative consequences. An analysis of genetic variation and inbreeding levels from 2005 to 2023 shows that gene flow between many subpopulations remains insufficient, despite the growing overall population.
“We must avoid further loss of genetic variation and increased inbreeding. To achieve this, it is essential to facilitate gene flow between subpopulations,” says Flagstad.
The project will therefore adapt existing measures, such as establishing feeding sites between larger core populations, to encourage fox migration and the colonization of new areas, as well as to promote genetic links between subpopulations. Where natural connections are lacking, targeted translocations of individual animals between subpopulations may also be necessary.
The project team also plans to conduct a simulation study this year to examine how the impact of reintroduced Arctic foxes can be optimized.
“The goal is to ensure that the genetic diversity of the Fennoscandian Arctic fox population keeps pace with the increase in the number of individuals. Hopefully, the population will continue to grow towards the vision of 2,000 adult Arctic foxes, while the measures we describe contribute to maintaining a genetically healthy population,” says Flagstad.
The genetic stabilization of the population remains a key challenge. The coming years will show whether the planned measures are sufficient.