Harvesting and culling are methods used to monitor and manage wildlife diseases. An important consequence of these practices is a change in the genetic dynamics of affected populations that may threaten their long-term viability. The effective population size (N_e) is a fundamental parameter for describing such changes as it determines the amount of genetic drift in a population. Here, we estimate N_e of a harvested wild reindeer population in Norway. Then we use simulations to investigate the genetic consequences of management efforts for handling a recent spread of chronic wasting disease, including increased adult male harvest and population decimation. The N_e/N ratio in this population was found to be 0.124 at the end of the study period, compared to 0.239 in the preceding 14-year period. The difference was caused by increased harvest rates with a high proportion of adult males (older than 2.5 years) being shot (15.2 % in 2005-2018 and 44.8 % in 2021). Increased harvest rates decreased N_e in the simulations, but less sex-biased harvest strategies had a lower negative impact. For harvest strategies that yield stable population dynamics, shifting the harvest from calves to adult males and females increased N_e. Population decimation always resulted in decreased genetic variation in the population, with higher loss of heterozygosity and rare alleles with more severe decimation or longer periods of low population size. A very high proportion of males in the harvest had the most severe consequences for the loss of genetic variation. This study clearly shows how the effects of harvest strategies and changes in population size interact to determine the genetic drift of a managed population. The long-term genetic viability of wildlife populations subject to disease will also depend on the population impacts of the disease and how these interact with management actions.

Data collection
The data was collected from the wild reindeer population at Hardangervidda in Southern Norway (60°09’55’’ N, 07°27’58’’ E). The Hardangervidda population is subject to annual harvest before the rut in late summer or the beginning of autumn (August-September). Generally, hunters do not differentiate between female and male calves, and it is also difficult to determine the sex of yearlings (1.5 years old) during hunting. Thus, harvest quotas generally separate between calves (0.5 years old), females (2.5 years and older), yearlings (females and males 1.5 years old), and free licenses (animals of any age and sex). The latter category is typically used to shoot adult males (2.5 years and older), as their size and status as trophy is considered attractive by hunters. Data on the number of harvested animals in each of the six categories (calves, yearlings, and adults of both sexes) were collected as reported by hunters.

Four different annual surveys are performed throughout the year to monitor the population size and structure. First, a minimum estimate for the population size is made using flight transects during mid-winter (January-March), where all observed groups of reindeer are photographed and counted. Second, the annual calf production is estimated using flight transects during summer (late June to mid-July), where a subset of groups with females, calves, and yearling males are photographed and the ratio of calves to adult females and yearlings of both sexes are calculated. Adult males generally aggregate in separate groups in other areas at this time of the year. Third, data is recorded on the number of calves, yearlings, and adults of both sexes that are shot during the harvest (August-September). Finally, the population age and sex structure are estimated using ground surveys just after the harvest (September-October). At this time of the year the reindeer aggregate in groups with both sexes and can be classified into age and sex classes (calves, females, yearling males, and adult males). Data on population sizes in the years 2005-2021 were collected from an established Bayesian integrated population model which uses data from these four surveys for this population (Viljugrein et al. 2023).

Additional data
Additional data on fertility for females, average summer survival for calves, and survival for adult animals in the Hardangervidda population were collected from Mysterud et al. (2020), data on mating skew for male reindeer were collected from Røed et al. (2005), data on primary sex ratio was collected from Loison and Strand (2005) and data on the distribution of age-specific fertilities were collected from Skogland (1985, 1989). These additional data are provided in the main text of the publication.

References

• Loison, A., Strand, O. 2005. Allometry and variability of resource allocation to reproduction in a wild reindeer population. Behavioural Ecology, 16: 624-633.
• Mysterud, A., Hopp, P., Alvseike, K.R., Benestad, S.L., Nilsen, E.B., Rolandsen, C.M., Strand, O., Våge, J., Viljugrein, H. 2020. Hunting strategies to increase detection of chronic wasting disease in cervids. Nature Communications, 11: 4392.
• Røed, K.H., Holand, Ø., Gjøstein, H., Hansen, H. 2005. Variation in male reproductive success in a wild population of reindeer. Journal of Wildlife Management, 69: 1163-1170.
• Skogstad, T. 1985. The effects of density-dependent resource limitations on the demography of wild reindeer. Journal of Animal Ecology, 54: 359-374.
• Skogstad, T. 1989. Natural selection of wild reindeer life history traits by food limitation and predation. Oikos, 55: 101-110.
• Viljugrein, H. 2023. Data and Figure-Scripts for the Paper ‘An Infectious Disease Outbreak and Increased Mortality in Wild Alpine Reindeer’. Zenodo. doi: 10.5281/zenodo.7624490