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Reducing effort while improving inference: Estimating Dall's sheep abundance and composition in small areas
Author(s) -
Schmidt Joshua H.,
Rattenbury Kumi L.
Publication year - 2013
Publication title -
the journal of wildlife management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.94
H-Index - 111
eISSN - 1937-2817
pISSN - 0022-541X
DOI - 10.1002/jwmg.557
Subject(s) - national park , distance sampling , abundance (ecology) , sample size determination , sampling (signal processing) , sample (material) , arctic , statistics , sampling design , physical geography , geography , environmental science , ecology , mathematics , biology , computer science , demography , population , chemistry , filter (signal processing) , chromatography , sociology , computer vision
Recent work has demonstrated that aerial distance sampling surveys are more efficient and effective than unadjusted minimum count surveys for estimating Dall's sheep ( Ovis dalli ) abundance, although large sample size requirements (e.g., 150–200 detections) may discourage implementation of these methods in small (<2,500 km 2 ) or low density areas. However, a Bayesian analytical approach using informed priors and borrowing detection information across surveys can increase precision and decrease required sample sizes. Using these methods, we conducted distance sampling surveys across a majority of the Dall's sheep habitat within National Park Service units in Alaska during 2010–2011. We compared 4 analytical scenarios using increasing amounts of detection information to demonstrate the increases in efficiency that can be gained over time through the use of this approach. Based on our analysis using all available survey information in the estimation of the detection function, we estimated that 2,252 (1,871–2,765), 2,809 (2,361–3,379), 1,669 (1,339–2,120), and 12,428 (10,780–14,470) sheep occurred in Denali National Park and Preserve (DENA), the Western Arctic National Parklands (WEAR), the Itkillik preserve subarea of Gates of the Arctic National Park and Preserve, and Wrangell‐St. Elias National Park and Preserve (WRST), respectively. These estimates were achieved with relatively small numbers of group detections in DENA ( n = 57), the Itkillik preserve area ( n = 48), and WEAR ( n = 100), suggesting that sample size requirements for Dall's sheep distance sampling surveys can be reduced by an additional 50–75% over previously recommended levels when adequate prior information is available. In addition, we describe a formal approach for estimating the size of individual composition classes (i.e., lambs, ewe‐like sheep,