title: Detection probability of vocalizing dugongs during playback of conspecific calls.
abstract: Dugongs (Dugong dugon) were monitored using simultaneous passive acoustic methods and visual observations in Thai waters during January 2008. Chirp and trill calls were detected by a towed stereo hydrophone array system. Two teams of experienced observers conducted standard visual observations on the same boat. Comparisons of detection probabilities of acoustic and visual monitoring between two independent observers were calculated. Acoustic and visual detection probabilities were 15.1% and 15.7%, respectively, employing a 300 s matching time interval. When conspecific chirp calls were broadcast from an underwater speaker deployed on the side of the observation boat, the detection probability of acoustic monitoring rose to 19.2%. The visual detection probability was 12.5%. Vocal hot spots characterized by frequent acoustic detection of calls were suggested by dispersion analysis, while dugongs were visually observed constantly throughout the focal area (p<0.001). Passive acoustic monitoring assisted the survey since detection performance similar to that of experienced visual observers was shown. Playback of conspecific chirps appeared to increase the detection probability, which could be beneficial for future field surveys using passive acoustics in order to ensure the attendance of dugongs in the focal area.
authors.affiliation: Graduate School of Informatics, Kyoto University, 606-8501 Kyoto, Japan. ichikawa@bre.soc.i.kyoto-u.ac.jp
authors.forename: Kotaro
authors.initials: K
authors.lastname: Ichikawa
authors.forename: Tomonari
authors.initials: T
authors.lastname: Akamatsu
authors.forename: Tomio
authors.initials: T
authors.lastname: Shinke
authors.forename: Kotoe
authors.initials: K
authors.lastname: Sasamori
authors.forename: Yukio
authors.initials: Y
authors.lastname: Miyauchi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Abe
authors.forename: Kanjana
authors.initials: K
authors.lastname: Adulyanukosol
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Arai
mesh_terms: D000161:Acoustic Stimulation; D000162:Acoustics / Q000295:instrumentation; D000818:Animals; D000835:Animals, Wild; D020454:Dugong; D015233:Models, Statistical; D009792:Oceans and Seas; D011336:Probability; D013018:Sound Spectrography; D013997:Time Factors; D014828:Vocalization, Animal