Report of a cetacean survey in the Western Approaches of the ...

Estimating a correction for both g(0) and responsive movementThe sightings made by the secondary platform included 5 sightings made with a radial distance < 600m.Based of our earlier findings, these sightings were likely to have been from animals which wereattracted to the vessel. To obtain a good ESW for the secondary platform, we excluded these 5sightings. However, 3 of these, sightings were duplicates which were included to give a usable samplesize when establishing an ESW for duplicates.Using Distance 4, we fitted a half-normal model with cosine adjustments to double platform (DP)effort data: secondary platform data to estimate f s (0); primary data to estimate f(0); and to duplicates toestimate f ps (0) (see Fig. 18). The truncation perpendicular distance for all data sets was 600m.The error for the correction factor c was estimated by carrying out a bootstrapping procedure on thesightings data from both platforms, partitioned by transect, and applying the variance estimationprocedure to each of 199 bootstrap data sets. The standard error of the bootstrap density estimate wasused as the standard error of c (s.e.(c); see Table 13).The CVs of corrected density and abundance estimates and the Satterthwaite degrees of freedom (df)for the corrected density and abundance estimate confidence intervals were calculated (see Table 13)Parameter (DP effort 2005)EstimateLength of transect, L (km) 514Truncation distance, w (km) 0.600Number of all secondary detections, n sall 19 (after truncation 17)Number of secondary detections > 0.600km, n s 14 (after truncation 12)Number of primary detections, n p 88Number of primary detections after truncation at 600m 86Number of duplicate detections, n ps 10ESW of secondary platform (sightings > 0.600 km), 1/f s (0) 1/3.16 = 0.316ESW for duplicates (km), 1/f ps (0) 1/3.53 = 0.283Apparent ESW for primary platform (km), 1/f(0) 1/5.15 = 0.194Apparent density estimate, D p (groups/km 2 ) Via equation (1)=0.431Corrected density estimate, D c (groups/km 2 ) Via equation (2)=0.291Primary detection probability ‘near’ trackline, g p (0) 0.931Correction factor, c 0.675Standard error of c, s.e. (c) 0.113Provisional density (ind/km 2 ) for 2004 survey0.688 (see Table 12)(Stratum E after stratification), D E 04 stratProvisional density (ind/km 2 ) for 2005 survey1.943 (see Table 12)(Stratum E after stratification), D E 05 stratProvisional density (ind/km 2 ) for 2004+2005 survey 1.097 (see Table 12)(Stratum E by stratification), D E 0405Corrected density (ind/km 2 ) for 2004 survey0.464 (CV 51%; 95% CI [0.17-1.26])(Stratum E after stratification), cD E 04 stratCorrected density (ind/km 2 ) for 2005 survey1.312 (CV=0.41; 95% CI [0.59-2.89])(Stratum E after stratification), cD E 05 stratCorrected density (ind/km 2 ) for 2004+2005 survey 0.74 (CV=0.39; 95% CI [0.34-1.59])(Stratum E by stratification), cD E 0405Table 13. Components from which a correction for movement and for animals missed on the tracklinewas calculated for common dolphin sightings data from 2005. The corrected density estimates forStratum E based on 2005 primary data and on 2004+2005 primary data by stratification has beencalculated using the correction factor.30