Harvest strategies for the elimination of low prevalence wildlife diseases

Abstract

The intensive harvesting of hosts is often the only practicable strategy for controlling emerging wildlife diseases. Several harvesting approaches have been explored theoretically with the objective of lowering transmission rates, decreasing the transmission period or specifically targeting spatial disease clusters or high-risk demographic groups. Here, we present a novel model-based approach to evaluate alternative harvest regimes, in terms of demographic composition and rates, intended to increase the probability to remove all infected individuals in the population during the early phase of an outbreak. We tested the utility of the method for the elimination of chronic wasting disease based on empirical data for reindeer ( Rangifer tarandus ) in Norway, in populations with (Nordfjella) and without (Hardangervidda) knowledge about exact disease prevalence and population abundance. Low and medium harvest intensities were unsuccessful in eliminating the disease, even at low prevalence. High-intensity harvesting had a high likelihood of eliminating the disease, but probability was strongly influenced by the disease prevalence. We suggest that the uncertainty about disease prevalence can be mitigated by using an adaptive management approach: forecast from models after each harvest season with updated data, derive prevalence estimates and forecast further harvesting. We identified the problems arising from disease surveillance with large fluctuations in harvesting pressure and hence sample sizes. The elimination method may be suitable for pathogens that cause long-lasting infections and with slow epidemic growth, but the method should only be attempted if there is a low risk of reinfection, either by a new disease introduction event (e.g. dispersing hosts) or due to environmental reservoirs. Our simulations highlighted the short time window when such a strategy is likely to be successful before approaching near complete eradication of the population.

Monitoring of chronic wasting disease (CWD) (IV)

“…The population size is therefore now lower and more female‐biased than before initiation of CWD management. It is nevertheless unlikely that the population sizes would be sufficiently reduced to have a high likelihood of removing all CWD‐infected individuals (Mysterud et al., 2021b ).…”

Harvest and decimation affect genetic drift and the effective population size in wild reindeer

“…Accordingly, the consequence of CWD infection in the population on Hardangervidda and the impact of suggested management strategies must be based on updated knowledge and carefully weighed against their likely impact on the population's genetic viability. Severe population reductions or the removal of populations can be the last resort to stop an outbreak (Mysterud et al, 2020(Mysterud et al, , 2021Mysterud & Rolandsen, 2018;Uehlinger et al, 2016). However, bottlenecks and reduced population sizes kept over longer time periods could have very negative consequences for the long-term genetic viability of wild populations due to genetic drift and loss of rare alleles.…”

“…Its population size is regulated by harvesting, but the annual population growth rate also depends on weather conditions (Bargmann et al., 2019). Male biased harvest and reductions in population size have been suggested as management efforts to prevent the spread of CWD in this population (Mysterud et al., 2021). The analyses are performed in four steps.…”

Ecosystem services from wildlife harvests

“…However, effective disease management employing wildlife harvesting often requires an integrated and adaptive management framework that considers disease and wildlife host attributes (e.g., Mysterud et al. 2021 ).…”