Josh Schmidt and Kumi Rattenbury with the Arctic I&M Network have a paper in the current edition of the Journal of Wildlife Management describing new methods for monitoring Dall’s sheep. The new methods are providing better information while reducing costs by as much as 80% over existing survey approaches.
The majority of sheep habitat in seven national park units, including Denali, Gates of the Arctic, Noatak, Kobuk Valley, Cape Krusenstern, Wrangell-St. Elias, and Lake Clark, was surveyed in 2010-12 using the new technique, and the estimated population for the surveyed park units is currently 26,000-28,000 individuals—similar to the number present in the early 1980s when many of the park units were formed.
The approach uses aerial distance sampling techniques to estimate overall population size as well as the composition (lambs, ewes, full curl rams, and < full-curl rams) of each population. It was first implemented in GAAR in 2009 where park-wide surveys were completed for the first time in nearly 30 years.
This is one of the few ways to get a rigorous estimate of both abundance and composition from the same survey. The higher quality data and lower costs will allow NPS to more consistently monitor populations and improve sheep management over time.
Aerial distance sampling is combined with an analysis that incorporates prior knowledge and information from other surveys to improve estimates. Using prior knowledge allows the scientists to get accurate estimates from areas with small or dispersed sheep populations, such as in Denali National Park and Preserve, as well as in areas with larger populations, such as in Gates of the Arctic.
Schmidt and Rattenbury are hopeful that this approach will help other agencies decrease costs and improve management of this species throughout Alaska. Balancing good science and minimizing costs is a constant challenge in Alaska, and this new approach gives both. Several parks and the I&M program hope this will lead to a formal management plan for Dall’s sheep.