Performance Assessment of 'Gamma Distribution'-Shaped Detection Functions for Aerial Line Transect Surveys of Large Terrestrial Mammals

• Activity Number: 572
• Type: Topic Contributed
• Date/Time: Wednesday, August 4, 2010 : 2:00 PM to 3:50 PM
• Sponsor: Section on Statistics and the Environment
• Author(s): Joel Howard Reynolds*+ and Anna-Marie Benson
• Companies: U.S. Fish and Wildlife Service and University of Alaska, Fairbanks
• Keywords: distance sampling ; monitoring ; wildlife management ; GammaMRDS ; software ; R

Abstract

Distance sampling from a small plane can create a detection function whose peak occurs off the inner edge of the search strip. This prompted development of a distance sampling approach using 'gamma distribution'-shaped detection functions (Becker and Quang, JABES 2009). Estimator bias and precision of this approach were investigated by simulating surveys of a brown bear (ursus arctos) population in southwest Alaska, USA. Density estimates were unbiased but estimates of some detection function parameters were highly biased. Standard errors were overestimated. Other simulations showed biased density estimates when observers were not truly independent. The approach's feasibility for monitoring large terrestrial mammals in Alaska is discussed in light of the required survey effort and costs, as is the reliance on double-observer mark recapture from a single platform.