Calf/female ratio and population dynamics of wild forest reindeer in relation to wolf and moose abundances in a managed European ecosystem

Background The alternative prey hypothesis describes the mechanism for apparent competition whereby the mortality of the secondary prey species increases (and population size decreases decreases) by the increased predation by the shared predator if the population size of the primary prey decreases. Apparent competition is a process where the abundance of two co-existing prey species are negatively associated because they share a mutual predator, which negatively affects the abundance of both prey Here, we examined whether alternative prey and/or apparent competition hypothesis can explain the population dynamics and reproductive output of the secondary prey, wild forest reindeer (Rangifer tarandus fennicus) in Finland, in a predator-prey community in which moose (Alces alces) is the primary prey and the wolf (Canis lupus) is the generalist predator. Methods We examined a 22-year time series (1996–2017) to determine how the population size and the calf/female ratio of wild forest reindeer in Eastern Finland were related to the abundances of wolf and moose. Only moose population size was regulated by hunting. Summer predation of wolves on reindeer focuses on calves. We used least squares regression (GLS) models (for handling autocorrelated error structures and resulting pseudo-R2s) and generalized linear mixed (GLMs) models (for avoidance of negative predictions) to determine the relationships between abundances. We performed linear and general linear models for the calf/female ratio of reindeer. Results and synthesis The trends in reindeer population size and moose abundance were almost identical: an increase during the first years and then a decrease until the last years of our study period. Wolf population size in turn did not show long-term trends. Change in reindeer population size between consecutive winters was related positively to the calf/female ratio. The calf/female ratio was negatively related to wolf population size, but the reindeer population size was related to the wolf population only when moose abundance was entered as another independent variable. The wolf population was not related to moose abundance even though it is likely to consist the majority of the prey biomass. Because reindeer and moose populations were positively associated, our results seemed to support the alternative prey hypothesis more than the apparent competition hypothesis. However, these two hypotheses are not mutually exclusive and the primary mechanism is difficult to distinguish as the system is heavily managed by moose hunting. The recovery of wild forest reindeer in eastern Finland probably requires ecosystem management involving both habitat restoration and control of species abundances.

The relationship between quotas and harvest in the alpine reindeer population on Hardangervidda, Norway

Hunting of cervids is commonly regulated by quotas that are specific to sex and age groups. There is substantial cultural variation in how quotas are regulated. In Scandinavia, the entire quotas are often not shot making deer management potentially less predictable. However, the effect of quota size and demographic composition on harvest offtake by recreational hunters has, to a limited extent, been empirically investigated in Scandinavia. Hunters are limited by time and opportunity and may not respond to changes in quota, as anticipated by managers. We analysed the variation in the proportion of quotas filled depending on quota size relative to population size and demographic composition of quotas during the period of 1986–2019 involving a population size varying from approximately 5000 to 15,000 reindeer on Hardangervidda, Norway. We found that the proportion of quota being filled by hunters varied substantially (12–48%) on an annual basis. The quota occasionally exceeded the estimated population size, but the proportion of the quota filled increased the higher the population size was relative to the quota size. The proportion of quota being filled by hunters was markedly lower for calf licences. High annual variation in the proportion of quota being filled by hunters causes considerable implementation uncertainty when managers aim to regulate cervid populations. Nevertheless, there was a strong correlation between quota size and harvest size. Facing new management requirements, a harvest rate of ~ 47% of the adult male population size was achieved in 2019, compared to an average of 16%. Hence, managers compensated for the low proportion of quota being filled by increasing quotas to reach target harvesting aims, but there remains a limit as to how precisely such a wide-ranging reindeer population can be regulated using recreational hunters.

Reindeer Anthrax in the Russian Arctic, 2016: Climatic Determinants of the Outbreak and Vaccination Effectiveness

The Yamal Peninsula in the Russian Federation experienced a massive outbreak of anthrax in reindeer (Rangifer tarandus) in July–August 2016, with 2,650 (6.46% of the total susceptible population) animals infected, of which 2,350 died (case fatality rate of 88.67%). In our study, we analyzed climatic and epidemiological factors that could have triggered the outbreak. The cancelation of reindeer vaccination against anthrax in 2007 resulted in an increase in population susceptibility. In response to the outbreak, total vaccination of all susceptible animals was resumed. To assess the vaccination effectiveness, we tested 913 samples of blood serum taken from vaccinated reindeer using an antigenic erythrocyte diagnostic kit to detect specific anti-anthrax antibodies via an indirect hemagglutination assay (IHA) 9 months after vaccination. We found that 814 samples had sufficiently high levels of anti-anthrax antibodies to indicate a protection level of 89% (95% confidence interval: 87–91%) of the whole reindeer population. Abnormally high ambient temperature in the summer of 2016 contributed to the thawing of permafrost and viable Bacillus anthracis spores could have become exposed to the surface; the monthly average air temperatures in June, July, and August 2016 were 20–100% higher than those of the previous 30-year period, while the maximum air temperatures were 16–75% higher. Using the projected climate data for 2081–2100 according to the “worst case” RCP8.5 scenario, we demonstrated that the yearly air temperature may average above 0°C across the entire Yamal Peninsula, while the yearly number of days with a mean temperature above 0°C may rise by 49 ± 6 days, which would provide conditions for reactivation of soil anthrax reservoirs. Our results showed that the outbreak of anthrax occurred under conditions of a significant increase in air temperature in the study area, underlined the importance of vaccination for controlling the epidemic process, and demonstrated the effectiveness of monitoring studies using the IHA diagnostic kit for detecting erythrocyte anthrax antigens.

Geographical Distribution Of Dioxins, Cadmium And Mercury Concentrations In Reindeer Liver, Kidneys And Meat In The Russian Far North

Reindeer herding is a vitally important agricultural sector in the Russian Far North. It is believed, that Nothern ecosystems are prone to accumulation of persistent pollutants for the reasons of trophical chains, features and climate. Reindeers graze on vast areas, having seasonal migrations on distances up to hundreds kilometers in one side in North-South direction, that increases likehood to cross a locally polluted area. Here we present results of a large-scale countrywide study of reindeer liver, kidneys and meat pollution by dioxins, cadmium and mercury. Samples were taken in 2015-2020 years from 41 locations in 8 reindeer-herding regions of Russia. Dioxins were determined in 383 samples of liver and 13 of meat, cadmium and mercury – in 505 samples of liver, 315 of kidneys and 22 of meat. Dioxin pollution has shown a clear geographical trend: liver concentrations gradually decrease from the Western to the Eastern parts on the country, with the highest concentration of 76.5 pg/g of fat WHO-TEQ. The following factors are likely to explain the discovered trend: localization of chemical enterprises and density of reindeer population. The highest concentrations of metals were found in kidneys (7.3 mg/kg of cadmium and 1.1 mg/kg of mercury). The contribution of local sources to cadmium and mercury pollution was found to be less, than expected. We also speculate, that reindeer liver may serve as a good additional indicator of environmental pollution by the investigated contaminants.

Antler cannibalism in reindeer

Prion diseases constitute a class of invariably fatal and degenerative encephalopathies. Chronic Wasting Disease (CWD) is a contagious prion disease among cervids, which is spreading and causing marked population declines in USA and Canada. The first outbreak of CWD in Europe was discovered in a reindeer population in Norway in 2016. In the worst-case scenario with continental-wide spreading of CWD in Eurasia, an annual harvest of around 4 million cervids is at stake only in Europe, with huge economic and cultural significance. An in situ origin of CWD was suspected, and it appear urgent to identify the likely cause to prevent future emergences. Here, we document the novel phenomenon of extensive antler cannibalism prior to shedding among reindeer in the CWD-infected population. The extent of antler cannibalism increased over the last decades when CWD emerged, and included ingestion of vascularized antlers. Ingestion of tissues from conspecifics is a risk factor for the emergence of prion diseases, where the presence of extensive antler cannibalism opens the intriguing possibility of a ‘Kuru-analogue’ origin of CWD among the reindeer in Europe. Based on general insight on pathology of prion diseases and strain selection processes, we propose an hypothesis for how contagious CWD may emerge from sporadic CWD under the unique epidemiological conditions we document here. More research is required to document the presence of prions in reindeer antlers, and whether antler cannibalism actually led to a strain selection process and the emergence of a contagious form of CWD from a sporadic form of CWD.

Reindeer fidelity to high quality winter pastures outcompete power line barrier effects

We investigated barrier effects of a 66 kV power line established in 1966 before and after the line was upgraded to 132 kV in 2004 over a period of 44 years (1974-2017) in the North Ottadalen wild reindeer area (3245 km2) of which 1038 km2 are in use as winter pastures. The power line transects a peninsula (135 km2) with high quality winter pastures in the southeast periphery. The reindeer population originated from a nucleus herd of 402 animals of domestic origin released in the area in 1964-1965 and 100 resident wild animals. Yearly winter survey started in 1974 and reindeer were first surveyed south of the 66 kV power line in 1982. Comparing the number of animals recorded in the peninsula vs. the number of individuals expected relative to available grazing area during the three periods (1974-2004, 1982-2004 and 2005-2017), the number of animals recorded in the peninsula was 3.6–4.9 times higher than expected. Since the upgrade of the power line, a substantial part of the reindeer population grazed in the peninsula every year. We therefore conclude that there was no long-term barrier effect from the original power line and no barrier effects at all from the upgrade. However, during the first 5 surveys of this study, there were no animals in the peninsula. Therefore, even if there are several possible reasons for this, we cannot exclude the possibility of short-term barrier effects resulting from the construction of the original power line. Our results support recent studies that report no effects from existing power lines and contrast some previous findings that have reported strong long-term barrier and avoidance effects of such infrastructure for Rangifer migration and grazing behaviour.