Series: Dall Sheep in Alaska's National Parks

Media Included

  1. Aerial Monitoring - Learn how scientists monitor Dall sheep. *** Note: This video contains no sound.

Discover how and why scientists monitor Dall sheep in national parks throughout Alaska.

Monitoring

A group of three dall sheep walk down a dirt road

NPS Photo / Charlotte Bodak

National Park Service Scientists conduct long-term monitoring on Dall sheep in Noatak National Preserve, Kobuk Valley National Park, and Gates of the Arctic, Denali, Wrangell-St. Elias and Lake Clark National Parks and Preserves. The primary goal of this program is to determine trends in the abundance and distribution of sheep in these parklands.

Scientists fly transect surveys in the mountains, noting all sheep on the uphill side of the aircraft, and analyze the data using statistical modeling to estimate the number and sex and age composition of sheep in these parks. In addition, NPS scientists are monitoring composition and diet and forage quality of sheep in two harvest management areas in the Brooks Range. Dall sheep populations declined considerably in the early 1990s but seem to be recovering. This long-term monitoring program will help address uncertainties about our knowledge of sheep populations.

Research Article: Using Distance Sampling and Hierarchical Models to Improve Estimate

There are over 27,000 square miles of potential sheep habitat in Alaska’s national parklands. Monitoring the animals is an enormous task. NPS scientists have developed methods for surveying sheep that maximizes the strength of the study while minimizing cost.

A professional article on the new method was recently published in The Journal of Wildlife Management:

JOSHUA H. SCHMIDT,1 Central Alaska Network, National Park Service, 4175 Geist Road, Fairbanks, AK 99709, USA
KUMI L. RATTENBURY, Arctic Network, National Park Service, 4175 Geist Road, Fairbanks, AK 99709, USA
JAMES P. LAWLER, Arctic Network, National Park Service, 4175 Geist Road, Fairbanks, AK 99709, USA
MARGARET C. MACCLUSKIE, Central Alaska Network, National Park Service, 4175 Geist Road, Fairbanks, AK 99709, USA


Article Abstract

Management of large mammal populations has often been based on aerial minimum count surveys that are uncorrected for incomplete detection and lack estimates of precision. These limitations can be particularly problematic for Dall sheep (Ovis dalli dalli) due to the high cost of surveys and variation in detection probability across time and space. The limitations of these methods have been recognized for some time, but previously proposed alternatives for sheep surveys proved to be too costly and logistically unfeasible in most circumstances (Udevitz et al. 2006).

We assessed the potential for a combination of distance sampling surveys and a hierarchical modeling approach to provide a more efficient means for estimating Dall sheep abundance by conducting aerial contour transect surveys over all sheep habitat in Gates of the Arctic National Park and Preserve (GAAR), Alaska in 2009 and 2010.We estimated the population of Dall sheep was 8,412 (95% CI: 6,517–11,090) and 10,072 (95% CI: 8,081–12,520) in 2009 and 2010, respectively.

Abundance within the Itkillik Preserve area within GAAR was 1,898 (95% CI: 1,421–2,578) and 1,854 (95% CI: 1,342– 2,488) in 2009 and 2010, respectively. Estimates of lamb abundance in 2010 were more than double those of 2009 after correcting for detection bias related to group size, suggesting that the apparent estimate of lambs in the population may be biased in some years depending on the degree of aggregation. Overall, the contour transect surveys were feasible logistically, cost 70–80% less than minimum count surveys, and produced precise estimates of abundance, indicating that the application of these methods could be used effectively to increase the statistical rigor and spatial extent of Dall sheep abundance surveys throughout Alaska.

These methods could be used to improve the assessment of long-term trends in populations and productivity and provide valuable information for harvest management at both local and landscape scales at reduced costs in comparison to traditional minimum count surveys. © 2011 The Wildlife Society.