Dispersal between reindeer subpopulations.
Report to Svalbard Environmental Protection Fund 22/3
By: Åshild Ønvik Pedersen, Liv Monica Trondrud, Larissa T. Beumer, Marie-Anne Blanchet, John M. Fryxell, Mathilde Le Moullec, Maud Therrien, Vebjørn Veiberg, Ronny Aanes and Brage B. Hansen.
Summary
Climate change is affecting biodiversity in all the Earth’s ecosystems through habitat modifications. The Arctic is warming at an unprecedented rate, fueling the decrease of sea ice. The coastal areas of Svalbard are experiencing a massive loss of fast ice in the fjords especially on the western part of the archipelago, thus isolating peninsulas from each other. The Svalbard reindeer, a key species of the terrestrial ecosystem, inhabits these coastal habitats. The population dynamics are driven by foraging conditions and density-dependent effects. However, little is known about their current seasonal range displacement and dispersal abilities and how this is affected by environmental changes. The purpose of the project was to explore how climate change may affect dispersal and range displacement among coastal semi-isolated populations. To do so, we GPS-marked 34 calves (2022-2024) on three neighboring peninsulas on the west coast of Svalbard in Forlandsundet (Brøggerhalvøya, Sarsøyra and Kaffiøyra). We also used two long-term datasets from the same area using GPS (2014-2024) and VHF collars (1998-2008) on adult females.
Only one of the GPS-marked calves moved between peninsulas; a newly marked male (10 months old) moved from Kaffiøyra to Sarsøyra in 2023, a year with a major population crash at Kaffiøyra (40 % decline between summers 2022 and 2023). The calf died just after dispersing. Of the six remaining calves equipped with GPS-collars in Kaffiøyra that spring, four died the same year. In our ongoing capture-mark- recapture study, only six marked reindeer (<2 %; n=4 males, n=2 females) out of 323 (n=237 females, n=86 males) are known to have moved between the peninsulas, either based on GPS-collar data or resightings. An earlier mark-resighting study (1998-2008) found that, in some years, up to 35 % of the adult females migrated seasonally between Sarsøyra and Brøggerhalvøya. In the early 2000’s, fjord ice was normally present between the peninsulas in parts of winter, and high reindeer densities in Brøggerhalvøya seemed to favour winter migration to Sarsøyra. High densities and poor winter forage accessibility also triggered major dispersal events in the 1990’s.
We suggest that the recent lack of movement between peninsulas, despite many severe winters, is due to the virtual absence of fjord ice as dispersal corridor. The reindeer sub-populations are increasingly isolated, which may cause inbreeding and loss of genetic diversity. The population genetics related to this are currently under study. Isolated populations are more at risk of extirpation under stochastic events, such as disease outbreaks or extreme weather events. The present study adds to our knowledge of changes in spatial distribution and population exchange of Svalbard reindeer, with implications for their long-term viability in a rapidly changing environment.
