Tuesday, November 10, 2015

Culling Koalas for Conservation

Guest post by Stefanie Thibert, who is currently enrolled in the Professional Masters of Environmental Science program at the University of Toronto-Scarborough

Euthanizing diseased koalas may be the most effective management strategy to save koalas from extinction in Queensland. A recent study published in the Journal of Wildlife Disease suggests that if 10% of terminally diseased and sterile koalas were culled while other infected koalas were treated with antibiotics, chlamydial infections could be completely eliminated and population sizes could increase within four years. 
The beloved koala relaxing in a eucalyptus tree

Although koalas are under pressure from habitat degradation, dog attacks and road accidents, disease burden is the largest threat to its population sizes. It is estimated that 50% of the current koala population in South-East Queensland is infected with the Chlamydia spp. The sexually transmitted disease causes lesions in the genitals and eyes, leading to blindness, infertility, and ultimately death. Rhodes et al. (2011) suggest that reversing the observed population decline in Queensland koalas would require either entirely eliminating deaths from cars and dogs, complete reforestation, or reducing deaths caused by Chlamydia by 60%. It is clear that the best conservation tool is to reduce the prevalence of chlamydial infection.

In the study, Wilson et al. (2015) examined the potential impact of euthanizing koalas infected with Chlamydia. As shown in Figure 1, computer simulation models were used to project koala population sizes based on four separate intervention programs: “no intervention”, “cull only”, “treat only”, and “cull or treat”. In the “cull or treat” program, sterile and terminal koalas were euthanized, while infected kolas that were not sterile or terminal were treated with antibiotics. It was concluded that the “cull or treat” is the most successful intervention program for increasing long-term population growth and eliminating chlamydial infections. 
The projected numbers of koalas in the Queensland population under different intervention programs.(From Wilson et al. 2015)
Without intervention, it is estimated that merely 185 koalas will persist in 2030. Under both the “cull only” and “treat only” intervention, it would take seven years before there would be greater koalas numbers than there would be without intervention. Under the “cull or treat” program, the population size was projected to overtake the no-intervention population after four short years. The population size in 2030 is also greatest under the “cull or treat” intervention. The increase in koala numbers in the “cull or treat” strategy is due to the considerable decrease in the prevalence of Chlamydia.
As expected, the proposal received considerable attention and was scrutinized by the public. Some argue that it is inhumane, while others suggest alternative management strategies. However, when it comes down to it, the science is clear. Euthanizing can be done in a humane way, and it is the most effective method for conservation of the species. The only real alternative to culling is treatment with antibiotics, which is costly, requires an immense amount of monitoring, and has been shown to take much longer to eliminate the disease and increase population sizes.
The question we must ask ourselves is: we cull other species, so why not koalas? For instance, in the United States, the culling of four million cattle successfully prevented bovine tuberculosis from spreading to humans. Even when based on sound scientific research, culling has always been dismissed as a management option for the iconic Australian marsupial. In 1997, culling was suggested as a method to protect the overabundant koala population on Kangaroo Island, but sterilization and relocation was used instead. It is amazing that a program that was significantly more expensive and less effective was chosen because the public could never think of killing the adorable and innocent koala.
Managing koala populations is clearly a case in which science intersects with emotion. However, it is essential that we put our emotions aside, and make a decision that is based on scientific evidence. Let us remember that the study only suggests culling or treating 10% of the population each year, which is equivalent to approximately 140 koalas. It is also important to improve the communication of science to the public. It needs to be made abundantly clear that without culling, the koala populations will continue to decrease.

To read the full article visit: http://www.bioone.org/doi/full/10.7589/2014-12-278 


Oliver, M. (2015, October, 20). Proposal to euthanise koalas with chlamydia divides experts. The Guardian. Retrieved from: http://www.theguardian.com/world/2015/oct/20/proposal-to-euthanise-koalas-with-chlamydia-divides-experts.

Olmstead, A.L., & Rhode, P.W. (2004). An impossible undertaking: The eradication of bovine tuberculosis in the United States. Journal of Economic History, 64, 734-772.

Rhodes, J.R., Ng, C.F., de Villiers, D.L., Preece, H.J., McAlpine, C.A., & Possingham, H.P. (2011). Using integrated population modeling to quantify the implications of multiple threatening processes for a rapidly declining population. Biological Conservation, 144, 1081–1088.

Wilson, D., Craig, A., Hanger, J., & Timms, P. (2015). The paradox of euthanizing koalas to save populations from elimination. Journal of Wildlife Diseases, 51, 833-842.

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