Feeding behavior of wild dugongs monitored by a passive acoustical method

Tsutsumi, Chika; Ichikawa, Katsuhiko; Arai, Nobuaki; Akamatsu, Tomonari; Shinke, Tomio; Hara, Takeshi; Adulyanukosol, Kanjana

doi:10.1121/1.2221529

Cited by 20 publications

(14 citation statements)

References 12 publications

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“…In Thailand, dugong calls were frequently recorded between 0300 and 0500 (Ichikawa et al . 2006), and feeding sounds of dugongs were only obtained at night (Tsutsumi et al . 2006).…”

Section: Resultsmentioning

confidence: 99%

Current Status and Conservation Needs of Dugongs in Southern Japan

Shirakihara

Yoshida

Yokochi

et al. 2007

Marine Mammal Science

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We conducted aerial surveys of dugongs (Dugong dugon) using the line‐transect method and snorkeling surveys of dugong feeding trails in 1998 and 1999 around Okinawa Island (26°30′N, 128°00′E) and the Sakishima Islands, southern Japan. A total of ten dugongs were sighted and feeding trails were confirmed in the sea grass beds off the east coast of Okinawa Island. In the Sakishima Islands, however, no dugongs were observed, and there was no evidence of feeding trails despite the existence of apparently suitable sea grass beds for feeding. The results of these surveys and other available information suggest that Okinawan dugongs represent a small, geographically isolated population. Our sightings of dugongs during the daytime, offshore of sea grass beds where feeding trails were recorded, suggest that Okinawan dugongs principally feed at night when human activities are limited. Survival of this remnant dugong population is threatened by habitat degradation and occasional entanglement mortality in fishing nets.

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“…In Thailand, dugong calls were frequently recorded between 0300 and 0500 (Ichikawa et al . 2006), and feeding sounds of dugongs were only obtained at night (Tsutsumi et al . 2006).…”

Section: Resultsmentioning

confidence: 99%

Current Status and Conservation Needs of Dugongs in Southern Japan

Shirakihara

Yoshida

Yokochi

et al. 2007

Marine Mammal Science

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“…Such vocal exchanges may also benefit dugongs, because they are often found closer to the shore during the night (Sheppard et al, 2009 and2010;Ichikawa et al, 2006;Tsutsumi et al, 2006;Marsh and Rathbun, 1990) and in turbid shallow waters (Hines, 2005;Pollock et al, 2006;Marsh et al, 2002). Given that Florida manatees exchange vocalizations frequently during separation (O'Shea and Poché, Jr., 2006) and that Amazonian manatees have vocal signatures (Sousa-Lima et al, 2002), dugongs are likely to have a similar vocalization pattern.…”

Section: B Distance Of Wild Dugongs From the Playback Sourcementioning

confidence: 95%

Callback response of dugongs to conspecific chirp playbacks

Ichikawa

Akamatsu

Shinke³

et al. 2011

The Journal of the Acoustical Society of America

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Dugongs (Dugong dugon) produce bird-like calls such as chirps and trills. The vocal responses of dugongs to playbacks of several acoustic stimuli were investigated. Animals were exposed to four different playback stimuli: a recorded chirp from a wild dugong, a synthesized down-sweep sound, a synthesized constant-frequency sound, and silence. Wild dugongs vocalized more frequently after playback of broadcast chirps than that after constant-frequency sounds or silence. The down-sweep sound also elicited more vocal responses than did silence. No significant difference was found between the broadcast chirps and the down-sweep sound. The ratio of wild dugong chirps to all calls and the dominant frequencies of the wild dugong calls were significantly higher during playbacks of broadcast chirps, down-sweep sounds, and constant-frequency sounds than during those of silence. The source level and duration of dugong chirps increased significantly as signaling distance increased. No significant correlation was found between signaling distance and the source level of trills. These results show that dugongs vocalize to playbacks of frequency-modulated signals and suggest that the source level of dugong chirps may be manipulated to compensate for transmission loss between the source and receiver. This study provides the first behavioral observations revealing the function of dugong chirps.

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“…Over the past several years, passive acoustic methods have been widely applied for monitoring dolphins ͑Philpott et al, 2007͒, porpoises ͑Wang et al, 2005͒, baleen whales ͑Stafford et al, 2007͒, and even for sirenians such as manatees ͑Phillips et al, 2004͒ anddugongs ͑Ichikawa et al, 2006;Tsutsumi et al, 2006͒. Dugongs produce several types of sounds such as chirps, trills, and barks.…”

Section: ͒mentioning

confidence: 99%

“…Underwater dugongs are visible in shallow areas such as feeding grounds. Previously in Thailand, several visual surveys were conducted to estimate the total population of about 120 animals in Trang Province ͑Hines et al, 2005͒, and acoustic observations of the dugongs suggested tidal and diel effect on their acoustic activities ͑Ichikawa et Tsutsumi et al, 2006͒. Although those previous works provided important information of the dugongs, the detection performances of the visual and acoustic observation remain to be evaluated.…”

Section: Introductionmentioning

confidence: 98%

Detection probability of vocalizing dugongs during playback of conspecific calls

Ichikawa

Akamatsu

Shinke³

et al. 2009

The Journal of the Acoustical Society of America

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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.

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Feeding behavior of wild dugongs monitored by a passive acoustical method

Cited by 20 publications

References 12 publications

Current Status and Conservation Needs of Dugongs in Southern Japan

Current Status and Conservation Needs of Dugongs in Southern Japan

Callback response of dugongs to conspecific chirp playbacks

Detection probability of vocalizing dugongs during playback of conspecific calls

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