From echolocation clicks to animal density—Acoustic sampling of harbor porpoises with static dataloggers

TitleFrom echolocation clicks to animal density—Acoustic sampling of harbor porpoises with static dataloggers
Publication TypeJournal Article
Year of Publication2012
AuthorsKyhn, Line, Tougaard Jakob, Thomas Len, Duve Linda, Stenback Joanna, Amundin Mats, Desportes Geneviève, and Teilmann Jonas
JournalJournal of the Acoustical Society of America
Volume131
Pagination550-560
EndNote Rec Number9646
Abstract

Monitoring abundance and population trends of small odontocetes is notoriously difficult and labour intensive. There is a need to develop alternative methods to the traditional visual line transect surveys, especially for low density areas. Here, the prospect of obtaining robust density estimates for porpoises by passive acoustic monitoring (PAM) is demonstrated by combining rigorous application of methods adapted from distance sampling to PAM. Acoustic dataloggers (T-PODs) were deployed in an area where harbour porpoises concurrently were tracked visually. Probability of detection was estimated in a mark–recapture approach, where a visual sighting constituted a “mark” and a simultaneous acoustic detection a “recapture.” As a distance could be assigned to each visual observation, a detection function was estimated. Effective detection radius of T-PODs ranged from 22 to 104 m depending on T-POD type, T-POD sensitivity, train classification settings, and snapshot duration. The T-POD density estimates corresponded to the visual densities derived concurrently for the same period. With more dataloggers, located according to a systematic design, density estimates would be obtainable for a larger area. This provides a method suitable for monitoring in areas with densities too low for visual surveys to be practically feasible, e.g., the endangered harbour porpoise population in the Baltic.