From echolocation clicks to animal density – acoustic sampling of harbour porpoises with static dataloggers

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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 TPOD 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.
Original languageEnglish
JournalAcoustical Society of America. Journal
Volume131
Issue1
Pages (from-to)550-560
Number of pages11
ISSN0001-4966
DOIs
Publication statusPublished - Jan 2012

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