Aerial survey of Dall’s sheep within Yukon-Charley Rivers National Preserve, July 2018

Joly, Kyle; Cameron, Matthew; Sorum, Mathew

A minimum count survey of Dall’s sheep (Ovis dalli) in Yukon-Charley Rivers National Preserve was conducted from July 14 to 16, 2018. The Preserve was last surveyed in July of 2015. The current survey examined the same 7 core mountain units as the previous survey and the Ogilvie Mountains were also surveyed. In the core area (the 7 units most often surveyed), 221 sheep (111 ewes, 39 lambs, 26 yearlings and 45 rams) were detected. This constitutes a 28% increase from the last (2015) survey, which had the lowest number of sheep ever reported (173). While the population has slightly rebounded since 2015, it is still approximately 30% below the 1997-2009 average of 313 sheep. There were 35 lambs, 23 yearlings, and 41 rams per 100 ewes in the core area. Lamb recruitment was the lowest ever recorded for the Preserve and was the 4th consecutive survey to detect a decline in this metric. If this trend continues, it could hamper population recovery in the Preserve. Yearling recruitment (26: 100 ewes) rebounded from its all-time low in 2015 (14: 100 ewes) but only equaled the long-term average from 1997-2009. The populations (Copper Mountain, Diamond Fork, Twin Mountain) that were small (total of 31 sheep combined in 2015) and had 4 or fewer ewes in them in 2015 all declined or at best remained the same size, dropping to 20 total sheep (an additional 35% from 2015). In contrast, the larger populations (5580 Mountain, Charley River, Cirque Lakes, Mount Sorenson) with 7 or more ewes in 2015 all increased, at least slightly. Overall this group of survey units increased by about 35% since 2015. Therefore, while the population is rebounding overall, it is more pronounced where a higher number of ewes are present. The survey units are relatively isolated and those units with few ewes and declining populations trends may take a longer time to recover because immigration will likely be limited in those areas until the other, more populous survey units make a more robust recovery. In the Ogilvie Mountains, 36 sheep were detected (14 ewes, 5 lambs, 2 yearling and 15 rams). This translates to 36 lambs, 14 yearlings and 107 rams per 100 ewes. These trends in age and sex ratio mirror those of the core area. Given the size of the unit and amount of potential sheep habitat, allotting more time to survey this unit in the future is recommended.

Aerial survey of Dall’s sheep within Yukon-Charley Rivers National Preserve, July 2018

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