Development of predictive elk population models to inform season proposals and aid in meeting population objectives for increasing and declining populations.
The purpose of this project is to develop elk population models to help inform elk season proposals created by Montana Fish, Wildlife and Park’s (FWP) wildlife biologists and managers. These models will be predictive, such that they will inform elk season recommendations created in the spring with regards to whether certain harvest levels in the fall will move populations toward objective by the following winter when populations are surveyed again. The models will be built and validated with existing, historical data, so that the predictive reliability of the tools is quantified and transparent. The intent of this project is to deliver a set of tools that can be commonly considered by biologists in the formulation of season proposals.
We anticipate that products from this effort will be useful for biologists that are attempting to decrease the size of elk populations to meet objective as well as in managing harvest for populations with low recruitment or that are below objective. In many cases, FWP biologists are charged with prescribing harvest levels for hunting districts where elk populations are above objectives established by the Fish & Wildlife Commission. In some cases these prescriptions are part of the seasons adopted by the Fish & Wildlife Commission, and whether or not the prescriptions are met will affect future hunting season regulations.
On the other end of the spectrum, biologists have highlighted a need to the develop consistent rationale for harvest prescriptions in areas where elk recruitment has become chronically low or is likely to decrease given recovery and population growth of large carnivores. Elk recruitment is unambiguously and negatively correlated with carnivore to elk, and wolf to elk, ratios where intensive studies have occurred in the Greater Yellowstone Area. Yet several factors complicate application of this research finding to elk management strategies even within the Montana portion of the GYA where intensive research has occurred, and very much so beyond the GYA.
While the negative correlation between recruitment and wolf to elk (and carnivore to elk) ratios is clear in GYA elk herds, the role of precipitation, habitat, and winter weather in affecting recruitment has been given more limited, indirect treatment in correlative studies in the Montana portion of the GYA. Observed recruitment ratios are the culmination of pregnancy, birth, and calf survival processes. Summer precipitation and the nutritional quality of elk forage have a large effect on adult female elk pregnancy and birth rates. Overwinter survival of elk calves is negatively correlated with severe winter weather in some areas. Further, while recruitment has a clear effect on elk population trend, survival of cow elk can also affect population trend. Cow elk survival is affected primarily by harvest, with only small documented effects of large carnivores, habitat, or weather. In many cases in the GYA where intensive research has occurred, liberal cow harvest has immediately preceded and even continued into periods of elk population declines, coincident with declines in recruitment. Lastly, the intensive (field-based) and extensive (using population monitoring data) research results to date in Montana have all come from the GYA, making application of results beyond GYA contentious, especially given the confounding roles of precipitation, habitat, winter weather, and cow survival (harvest) in elk population trends in the GYA.
The objectives of this analysis are:
Compile elk and carnivore monitoring data, as well as relevant covariates for precipitation, habitat, and winter weather, in a single location, so that population models can be developed,
Develop and validate predictive elk population models that quantify the roles of recruitment and harvest in affecting elk population trend using historical, existing data, and
Due to wide variability in recruitment across Montana, as well as complexity and confusion in the role of carnivores versus other factors in driving recruitment, develop predictive models of elk recruitment. The effect of a certain level of prescribed harvest on elk population trend is likely to depend on the level of recruitment in the population, and therefore incorporation of recruitment models will improve the predictive accuracy of elk population models. These models will include effects of carnivores, precipitation, habitat quality, and winter weather, and will be based on and validated using existing data.
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Introduction & Background