Table 1.

Proportion relative bias for the total abundance estimator ($\hat{N}$), as estimated from different models (indicated on rows), and as a function of different transect configurations (columns). (Each value represents median proportional bias of n= 100 simulation replicates, where the posterior predictive mean of $\hat{N}$ is used as a point estimator. Models could include landscape-level covariates (collectively referred to as ‘covs’), geographical stratum (‘stratum’), a measure of sampling intensity (intended as a potential fix for preferential sampling; ‘samp.dens’) and spatially autocorrelated ‘RE’. Different flight configurations are displayed in figure 4; the first arabic symbol in the flight name relates to the number of flights (4, 8 or 12 flights), while the second reflects the amount of effort devoted to nearshore surveys (1=no coastal surveys, 2=2 coastal surveys, 3=4 coastal surveys, 4=6 coastal surveys). Blank entries indicate cases where estimates were numerically unstable or models were otherwise overparametrized.)

	4 flights		8 flights			12 flights
model	A1	A2	B1	B2	B3	C1	C2	C3	C4
(a) bearded seals
covs	−0.03	0.54	−0.04	0.03	0.08	−0.00	0.06	0.07	−0.01
covs + samp.dens	0.18	0.15	−0.05	−0.08	−0.07	−0.06	−0.04	−0.02	−0.10
stratum		−0.07	−0.05	−0.05	−0.05	−0.05	−0.04	−0.05	−0.06
covs + stratum		0.14	−0.04	−0.07	−0.04	−0.05	−0.04	−0.03	−0.07
stratum + samp.dens		−0.07	−0.04	−0.07	−0.04	−0.06	−0.06	−0.01	−0.09
covs + stratum + samp.dens		0.12	−0.03	−0.04	0.01	−0.03	−0.05	−0.01	−0.07
covs + RE	−0.03	0.59	−0.03	0.01	0.04	−0.03	−0.01	0.01	−0.02
stratum + RE		−0.07	−0.06	−0.07	−0.05	−0.09	−0.05	−0.05	−0.07
stratum + samp.dens + RE		−0.08	−0.05	−0.06	−0.03	−0.06	−0.05	−0.02	−0.10
(b) ringed seals
covs	−0.01	0.19	0.04	0.09	0.13	0.04	0.06	0.10	0.07
covs + samp.dens	0.14	0.21	0.04	−0.00	−0.01	0.02	0.02	0.00	−0.02
stratum		0.09	−0.00	0.03	0.05	−0.02	−0.01	0.03	0.02
covs + stratum		0.10	−0.01	0.01	0.03	−0.00	0.00	0.02	0.00
stratum + samp.dens		0.05	−0.00	−0.01	−0.03	−0.02	−0.02	−0.01	−0.03
covs + stratum + samp.dens		0.10	−0.00	−0.02	−0.01	−0.01	−0.01	−0.01	−0.04
covs + RE	−0.02	0.13	−0.00	0.01	0.04	−0.01	−0.00	0.01	−0.01
stratum + RE		0.09	−0.00	0.03	0.06	−0.02	−0.00	0.02	0.02
stratum + samp.dens + RE		0.05	0.00	−0.02	−0.03	−0.02	−0.02	−0.01	−0.04
(c) polar bears
covs			0.01	−0.11	0.07	−0.04	−0.09	−0.05	−0.07
covs + samp.dens						0.02	0.02	−0.08	−0.04
stratum			−0.11	−0.07	0.19	−0.08	−0.07	−0.05	0.11
stratum + samp.dens			0.38	−0.05	0.04	−0.04	−0.01	−0.04	0.07