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Ongoing Study Suggests Elk Herds Increase Despite CWD

November 10, 2008.

From Wyoming Game and Fish:

A long-term Wyoming study looking at the effects of Chronic Wasting Disease on elk populations suggests the always-fatal disease may not cause precipitous declines in those populations.

Researchers at the Wyoming Game and Fish Department's Tom Thorne/Beth Williams Wildlife Research Center at Sybille have been looking at the long-term effects of CWD on an elk population since 2002.

"Though the study is not yet complete, there has been significant public interest in the study and what it might tell us about how CWD could affect overall populations of elk, especially elk that are artificially concentrated on Wyoming's winter feedgrounds," said Eric Keszler, WGFD's Public Information Officer. "We know that CWD is always fatal to individual animals, but we also know that animals may be infected for five years or more before they succumb to the disease, so they have a chance to reproduce multiple times. There has never been any research to look at how these factors might affect overall elk population trends in the presence of this disease. Our researchers did some preliminary estimates on the data we have so far to help give the public at least some initial ideas about what this study is telling us."

In 2002, 40 elk calves were captured at the National Elk Refuge and brought to Sybille for additional brucellosis research. Because of new federal regulations restricting research on brucellosis at that time, researchers decided to instead use the elk for a long-term CWD research project.

CWD has existed at Sybille for almost 30 years and most, if not all, elk and deer housed at Sybille eventually contract CWD, either from the environment or from other infected animals. CWD affects elk in the wild differently, and experts do not yet understand why some wild elk contract CWD and some don't-- or why some elk contract CWD before others. Researchers designed this study to allow the elk to live at Sybille until they became infected with CWD and died; document each animal's age, cause of death, and other data; and then develop models to help predict how elk populations might rise or fall as a result.

"We assume that the CWD mortality rates observed at Sybille would represent the most extreme exposure to the CWD infectious prion, because the elk would be exposed to the prion continuously throughout their lives," said Terry Kreeger, Veterinary Services Supervisor for the WGFD. "Thus, this research would be used to design a model to predict the effects of CWD on a wild elk population representing a worst-case scenario.

Thirty-one of the 40 original elk in the study have died so far, all from CWD. But most of the elk had one or more calves (not all of the elk were allowed to be bred every year). Researchers have used this data to estimate any future changes for this population of elk. "Accounting for calf production and recruitment and using simple life-table analysis, we estimate there would have been a 47-percent increase in this population," said Kreeger. "That is, there would be 59 elk surviving today from the original population of 40."

Kreeger warns that these data are preliminary and that it would be speculative at this point to try and extrapolate these data to any wild elk populations. Once all of the elk in the original study population have died, WGFD researchers will use data from wild elk populations to account for additional factors such as predation mortality, hunting mortality, production, and recruitment to model what effects CWD would have on a free-ranging population using state or federal feedgrounds, where elk are concentrated during the winter.

According to WGFD Assistant Wildlife Chief Scott Talbott: "Based on these preliminary data and our life table analysis, in the presence of CWD it appears the elk in this study would maintain a stable or increasing population."

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