Distance estimation experiment for aerial minke whale surveys

• Published in: NAMMCO Scientific Publications
• Main Authors: Witting, Lars, Pike, Daniel G
• Format: Article in Journal/Newspaper
• Language: English
• Published: Septentrio Academic Publishing 2009
• Subjects: minke whales; Balaenoptera physalus; surveys; distance estimation; minke whale
• Online Access: https://septentrio.uit.no/index.php/NAMMCOSP/article/view/2709; https://doi.org/10.7557/3.2709

A comparative study between aerial cue–counting and digital photography surveys for minke whales conducted in Faxaflói Bay in September 2003 is used to check the perpendicular distances estimated by the cue-counting observers. The study involved 2 aircraft with the photo plane at 1,700 feet flying above the cue–counting plane at 750 feet. The observer–based distance estimates were calculated from head angles estimated by angle-boards and declination angles estimated by declinometers. These distances were checked against image–based estimates of the perpendicular distance to the same whale. The 2 independent distance estimates were obtained for 21 sightings of minke whale, and there was a good agreement between the 2 types of estimates. The relative absolute deviations between the 2 estimates were on average 23% (se: 6%), with the errors in the observer–based distance estimates resembling that of a log-normal distribution. The linear regression of the observer–based estimates (obs) on the image–based estimates (img) was Obs=1.1Img (R2=0.85) with an intercept fixed at zero. There was no evidence of a distance estimation bias that could generate a positive bias in the absolute abundance estimated by cue–counting.