Fig 1.
Strip transect with encounter region.
Transect line (dashed grey line) with the strip extending a distance w out to either side (solid grey lines). The observer and encounter region at time t − 1 (dashed black) and t (solid black) are shown, together with an animal moving with speed u in direction θ
Fig 2.
Percentage bias in the abundance estimate for strip and line transects.
Bias for strip transect sampling (solid line) calculated from the analytic expression given and for line transects (hazard-rate b = 2) by averaging over 1000 simulations for linear movement (dashed line) and home range movement (dotted line)
Fig 3.
Estimated detection function for line transect sampling for increasing animal speeds.
Estimated detection function averaged over 1000 simulations for line transect sampling (hazard-rate b = 2) with the linear animal movement model at animal speeds 0% (black solid line), 20% (red dashed line), 40% (blue dotted line), 80% (green dotdash line), 150%(purple longdash line) and 200% (grey twodash line)
Fig 4.
Frequency of detections at each perpendicular distance from the line.
Estimated histogram of recorded distances averaged over 1000 simulations for line transect sampling (hazard-rate b = 2) with linear animal movement at animal speeds 0% (black solid), 20% (red dashed) 80%(green dotted) and 150% (purple dotdash)
Fig 5.
Percentage bias in abundance estimate for different shape parameter values.
Percentage bias in abundance estimate for linear movement against animal speed as a percentage of observer speed for shape parameters b = 2 (black solid), b = 3 (blue dashed) and b = 5 (red dotted) with percentage bias for a strip transect (grey solid) estimated from 1000 simulations included for comparison.
Fig 6.
Percentage bias in abundance estimate against distance observer looks ahead.
Percentage bias against distance observer looks ahead with hazard rate b = 2 and animal speeds 50% (red dotted), 100% (blue dashed) and 150% (black solid) of observer speed
Fig 7.
Percentage bias in abundance estimate for different truncation distances.
Percentage bias in abundance estimate averaged over 1000 simulations for hazard-rate b = 2 against truncation distance applied by the analyst for animal speeds 20% (red solid), 80% (green dashed) and 150% (purple dotdash)