The feeding and slaughter of elk and bison in the Greater Yellowstone for disease control

Background/Question/Methods The United States cattle herd became brucellosis free in February 2008.  However, the threat of transmission from elk and bison to cattle remains a significant concern in the Greater Yellowstone Ecosystem (GYE). To control brucellosis, state and federal managers feed more than 6000 metric tons of hay to elk and bison every year at 23 supplemental feedgrounds in the southern GYE. Meanwhile in the north, managers often cull bison leaving the Yellowstone National Park. This talk summarizes several ongoing and past studies on the ecology and management of brucellosis in this ecosystem. First, we investigate how climate and management interact to affect the seroprevalence of brucellosis in elk populations in the southern GYE. We then use modeling approaches to assess the role of dispersal in explaining spatial variation in prevalence as well as the potential efficacy of different control strategies. Finally, we will present preliminary analyses of GPS tracking study intended to investigate how the risk of brucellosis transmission from elk to cattle varies in space and time depending upon snowpack and habitat. Results/Conclusions Snowpack is strongly correlated with the duration of artificial elk feeding, which is strongly correlated with elevated seroprevalence of brucellosis on the elk feedgrounds. If these relationships reflect a causal process, then reducing the length of the feeding season by a month could drop seroprevalence by 2/3rds. Elk seroprevalence is highest around these supplemental feedgrounds (~26%) and is relatively low (1-3%) in other elk populations around the GYE. Using simple simulation models we show that the 2% seroprevalence of brucellosis in elk in northern Yellowstone is possible even with very limited movement of elk from the artificially fed populations in the south. Finally, we show the potential effectiveness of combining vaccination and contraception for reducing bison brucellosis. Controlling brucellosis in the GYE would require a multi-pronged effort on both bison and elk using a combination of veterinary (vaccination and contraception) and ecological approaches (manipulation of the elk feeding regime and cattle feeding allotments).