Elk monitoring in Mount Rainier and Olympic national parks: 2008 ‒ 2017 synthesis report

Jenkins, Kurt; Lubow, B.; Happe, Patti; Braun, K.; Boetsch, John; Baccus, W.; Chestnut, T.; Vales, David; Moeller, Barbara; Tirhi, Michelle; Holman, E.; Griffin, Paul

doi:10.36967/nrr-2286864

In 2008, the U.S. Geological Survey (USGS) began collaborating with the National Park Service (NPS)-North Coast and Cascades Network (NCCN), the Muckleshoot Indian Tribe (MIT), Puyallup Tribe of Indians (PTOI), and Washington Department of Fish and Wildlife (WDFW) to develop a standard survey protocol for monitoring long-term changes in the abundance, distribution, and population composition of elk on key summer ranges within Mount Rainier National Park (MORA) and Olympic National Park (OLYM). In MORA, surveys were conducted in two trend count areas (TCAs) that correspond with primary summer ranges used by the North Rainier Herd, which winters outside the park to the North, and the South Rainier Herd, which winters outside the park primarily to the South. In OLYM, we defined five TCAs including an Olympic Core TCA (hereafter, Core TCA) that encompasses summer ranges on the flanks of Mount Olympus, and four TCAs that encompass other primary summer ranges throughout the park. The standard protocol allows for estimating aerial survey detection biases and adjusting raw survey counts to account for elk that were likely present but not seen during surveys. Previously, we developed a suite of aerial-bias-correction models for use in estimating aerial detection biases and adjusting raw counts of elk in MORA based on sighting conditions related to elk group size, vegetation density, lighting conditions, elk movement, as well as combinations of these and other factors. The models were based on independent sighting records of elk groups by front-seat and back-seat observer pairs in a helicopter, including detection records of some radio-collared elk groups. Here, we analyze results of the first 10 years of elk monitoring in MORA (2008-2017) and 8 years in OLYM (2008-2015). In a previous report covering surveys conducted from 2008-2011, data were not sufficient to model detection biases of aerial surveys conducted in OLYM; hence, analyses of elk population trends were based on counts adjusted for detection biases in MORA, whereas trends in OLYM were based on raw, unadjusted counts (Griffin et al. 2013, Jenkins et al. 2015). Our objectives for the current summary were to: (1) incorporate additional data to update aerial-bias-correction models previously developed for use in MORA to include corrections for aerial detection bias in both MORA and OLYM, (2) examine trends in elk abundance, distribution, and population composition estimates for subalpine summer ranges within MORA and OLYM, and (3) estimate effects of seasonal variation and weather on elk abundance and population composition estimates for subalpine summer ranges in both parks. We updated previously developed aerial-bias-correction models based on 148 simultaneous double-observer sightability (DO-S) trials associated with elk groups containing radio-collared elk (45 in OLYM and 103 in MORA) and 1,653 simultaneous double-observer (DO) trials based on groups without radio-collared elk (288 in OLYM and 1,365 in MORA) acquired from 2008 to 2015. Aerial sightability varied among years, between parks, and in relation to individual sighting conditions, particularly elk group size and movement, vegetation cover, and lighting conditions. We estimated elk abundance and population composition by model-averaging individual estimates derived from 16 different bias-correction models, each including a variety of single variable and interactive effects. We conducted 13 surveys of North Rainer TCA and 15 of South Rainier TCA from 2008-2017. We estimated a mean of 359 (SE=34.6) elk present in North Rainier TCA and 477 (SE=50.2) elk in South Rainier TCA during surveys, which corresponds with mean densities of 3.5 and 5.3 elk/km2 in North (103.1 km2) and South Rainier (89.3 km2) TCAs, respectively. Elk abundance in North Rainier TCA increased at an estimated instantaneous annual rate (ro) of 0.039 (SE=0.028; 95% confidence interval [CI]= 0.02, 0.09) during the 10-year span, although the trend

Elk monitoring in Mount Rainier and Olympic national parks: 2008 ‒ 2017 synthesis report

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