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Ichikawa, Kotaro; Akamatsu, Tomonari; Shinke, Tomio; Adulyanukosol, Kanjana; Arai, Nobuaki
(detail)
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2011 |
Callback response of dugongs to conspecific chirp playbacks.
Journal of the Acoustical Society of America 129(6): 3623-3629. DOI: 10.1121/1.3586791. June 2011.
–ABSTRACT: 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 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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Cherdsukjai, Phaothep; Kittiwattanawong, Kongkiat; Adulyanukosol, Kanjana
(detail)
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2014 |
Dugong aerial surveys 2011-2012: declining trend of the dugong population in Muk-Talibong Island, Thailand.
Proc. Design Symposium on Conservation of Ecosystem (The 13th SEASTAR2000 Workshop) 2: 50-54. 4 tabs. 1 fig. Mar. 2014.
–ABSTRACT: The Muk-Talibong Islands in Trang Province are a habitat for the largest group of dugongs on Thailand's Andaman coast. Since 1994, the Phuket Marine Biological Center has regularly conducted aerial surveys over the area with various kinds of aircraft. In 2011 and 2012, the small aircraft model Tecnum P92J was used in line transect aerial surveys. Survey efforts were four flights (15.01 hours) and seven flights (17.14 hours) respectively. In 2011, the dugong detection rate was 51±50 animals per day, with a maximum count of 122 animals. In 2012, however, the dugong detection rate was 26±14 animals per day, with a maximum count of 54 animals. As a result of comparing the dugong detection rates for both years, we found that the number of dugongs is decreasing, even though the aerial survey periods in each year were the same month and tidal time. Windspeed is likely to be a physical factor that might lead to these results. Ranges of wind speed were 0-6 knot in 2011 and 5-17 knot in 2012. The wind speed affects waves and turbidity, and this may negatively affect visual detection of dugongs. Therefore, further aerial surveys in different weather conditions and dugong stranding reports may help to better understand the declining trends of dugongs in the area.
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Ponnampalam, Louisa S.; Fairul Izmal, J. H.; Adulyanukosol, Kanjana; Ooi, Jillian L. S.; Reynolds, John E., III
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2014 |
Aligning conservation and research priorities for proactive species and habitat management: the case of dugongs Dugong dugon in Johor, Malaysia.
Oryx 49(4):743-749. 4 figs. DOI: 10.1017/S0030605313001580. Published online, July 8, 2014; Oct. 2015.
–ABSTRACT: Conservation efforts use scientific data to provide an adaptive framework wherein habitat and wildlife sustainability can co-exist with human activities. Good science informs decision-makers and facilitates the development of successful conservation approaches. However, conservation concerns for the dugong Dugong dugon in South-east Asia are sufficiently urgent that action must be taken quickly, even though science has not provided complete answers to critical questions. In Johor, Malaysia, aerial surveys were conducted to assess dugong numbers, dugong high-use areas and overlap of dugong sightings with areas of seagrass. Dugong distribution included existing marine parks and locations where known conservation threats exist. We conclude that the Johor islands may represent a significant congregation site for dugongs in Peninsular Malaysia, with as many as 20 dugongs recorded in a single day. The existence of a marine park where the dugong sightings were most prominent is encouraging but only 38% of those sightings fell within the boundaries of the park. Anthropogenic threats need to be assessed and addressed prior to complex development activities such as dredging and coastal reclamation for tourism development in this critical area. We use this case to explore the concept of advancing species conservation through focused research and management, particularly where uncertainties exist because data are scarce.
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Bibliography and Index of the Sirenia and Desmostylia 