Estimating absolute abundance of harbour porpoise from small boat surveys using visual sightings and acoustic detections as independent observations

Speaker: Russell Leaper (Aberdeen) and Jonathan Gordon (SMRU) (SOI, St.Andrews University)

Abstract

A number of surveys have been conducted in recent years from small vessels in areas of harbour porpoise habitat with the aim of providing data for Environmental Impact Assessment of off-shore wind farm developments. Estimates of the numbers of animals likely to be affected and comparisons between areas require estimates of absolute abundance but these are difficult to obtain from small vessels which cannot accommodate independent observer platforms. Passive acoustics provide an automated and efficient way of detecting harbour porpoises and target motion analysis techniques can now provide estimates of the perpendicular distance to each detection. Combined visual and acoustic data have been used to set up trials to estimate g(0) for each detection method. Although results have been promising, there still remain some issues including duplicate identification that could benefit from further work.