A gamma-shaped detection function for line-transect surveys with mark-recapture and covariate data

Distance Sampling: Methods and Applications

“…5.4.1). Becker and Quang (2009) take this a step further. They do not offset the line, but model the fall-off in detectability under the aircraft.…”

Rejection of Schmidt et al.'s estimators for bear population size

“…Certainty about perfect detection at the detection apex is extremely difficult to obtain when aircraft is used. For aerially collected data, different MRDS models were developed by Manley, McDonald, and Garner (1996) for polar bears (Ursus maritimus), Quang and Becker (1996) for Pacific and common loons (Gavua pacifica and G. immer), Quang and Becker (1999) for brown bears (Ursus arctos), Becker and Quang (2009) for brown bears, and Becker and Christ (2015) for brown and black bears (Ursus americanus). Early development of MRDS models was driven in part by developing models for aerially collected data.…”

“…Laake and Borchers (2004) state that population estimates from MRDS models "obtained under the assumption of full independence will tend to be negatively biased compared to estimates obtained under the assumption of point independence." Schmidt et al (2017) justify dropping the MR model with the statement: "marginal detection probabilities at the apex of the detection function are quite high for both the pilot and observer (Becker & Christ, 2015;Becker & Quang, 2009;Walsh et al, 2010) suggesting that the joint p d may approach 1.0 in many cases." Schmidt et al (2017) justify dropping the MR model with the statement: "marginal detection probabilities at the apex of the detection function are quite high for both the pilot and observer (Becker & Christ, 2015;Becker & Quang, 2009;Walsh et al, 2010) suggesting that the joint p d may approach 1.0 in many cases."…”

“…We have observed this bias in numerous brown and black bear datasets (E. Becker, unpublished data). We note the Becker and Quang (2009) population estimate of 618.4 brown bears (26.3 brown bears/1,000 km 2 ) is much lower than the MRDS_2PN model estimate of 746.1 (Table 2) due mainly to un-modeled heterogeneity in the full independence model used by Becker and Quang (2009). Schmidt et al (2017) are not justified in dropping the MR data since 2 of their reported MR probabilities were calculated using a full independence MRDS model (Becker & Quang, 2009) and, as a result, are biased high due to un-modeled heterogeneity.…”

Line‐Transect Sampling, New Approaches

“…For example, Caughley and Grice [24] employed helicopters to estimate emus in Western Australia while both helicopters and fixed-wing aircraft were used to estimate feral abundance in western New South Wales [25]. Other examples include moose populations in Alberta [26] and brown bears in Alaska [27]. Dual observers are often used in this approach with mark-recapture theory employed for abundance estimates (see Capture-recapture methodology).…”