Statewide black bear density monitoring in Washington: A cross-region and interagency team approach

Black bear density estimates are necessary to assess population management objectives and understand the relationship between abundance, habitat characteristics, and harvest at varying scales. In Washington, statewide black bear abundance estimates are predicated on derivations made in the 1970’s and the 1990’s and hypothesized to be a function of habitat quality based on variations in precipitation and vegetation. To evaluate current black bear density and landscape relationships in Washington, WDFW conducted a 4‐year capture‐recapture study in 2 areas of the North Cascade Mountains using 2 detection methods, noninvasive hair collection/DNA analysis and physical capture-global positioning system (GPS) radiocollar (Welfelt et al. 2019). Within Game Management Units (GMUs) 245, 454, and 460, GPS telemetry locations were integrated with spatial capture‐recapture (SCR) data to create a SCR‐resource selection model to estimate density as a function of spatial covariates and test the hypothesis that density is higher in areas with greater vegetative food resources.

During this project, 118 bears were captured and collared 132 times and 7,863 hair samples were collected at hair traps where 537 individual bears were identified from 1,237 detections via DNA. The most‐supported model in the western North Cascades depicted a negative relationship between black bear density and an index of human development; average bear density was estimated to be 20.1 bears/100 km2, but density varied from 13.5/100 km2 to 27.8 bears/100 km2 depending on degree of human development. The model best supported by the data in the eastern North Cascades resulted in an average density estimate of 19.2 bears/100 km2, ranging from 7.1/100 km² to 33.6 bears/100 km²; density was positively correlated with primary productivity.

The hypothesis that greater precipitation and associated vegetative production in western Washington supports greater bear density compared to eastern Washington was not supported by our data. In western Washington, empirically derived average total density estimates (including cubs) were nearly 50% lower than managers expected prior to our research. In eastern Washington average black bear density was predominantly as expected, but localized areas of high primary productivity supported greater than anticipated bear densities. These stark differences illustrate the need to understand processes that affect population numbers and that updated, more formal monitoring is necessary. In 2019 we developed a rigorous monitoring protocol to estimate black bear population densities on a large scale. Using average capture probability and movement information from the North Cascades density analysis (Welfelt et al. 2019), we performed simulations to establish an optimized sampling design that would result in the least amount of staff time, materials, and expense to the agency. The resulting strategy was to select 2-3 project areas annually throughout the 17 Districts where bears occur to establish density estimates. As more surveys are conducted, additional capture results will further inform the model, therefore making density estimates more robust. As of 2022, Monitoring has been compiled in 14 study areas, with 12 having completed results (Figure 1) and similar research has been done in 2 other areas for a total of 18 GMUs where black bear density has been estimated.