Development of detection device for dugong calls

December 15-17, 2007, Royal Phuket City Hotel, Phuket, ThailandAn acoustical approach for research on marine mammals has been a very active research method in recent years. Dugong (Dugong dugon) is one of the highly endangered species, which are strictly-marine herbivorous and mainly inhabit coastal areas. In order to detect dugong calls from recorded data, several algorithms have been adapted by researchers in the analyzing process. However, the number of misses in the detection is still non-zero. The sound of snapping shrimp recorded in a wide range (2-300 kHz) is one of the main background noises that makes the detection of dugong calls difficult in warm shallow waters. Impulse elimination was employed in the system to get rid of the snapping shrimp noise. In order to improve the performance of the detection system by increasing the detection rate and decreasing the number of misses, two new algorithms were tested in the experiment. The experimental results for the new algorithms including impulse elimination and the cepstrum method are presented in this paper

An International Quiet Ocean Experiment

Author Posting. © Oceanography Society, 2011. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 24, no. 2 (2011): 174–181, doi:10.5670/oceanog.2011.37.The effect of noise on marine life is one of the big unknowns of current marine science. Considerable evidence exists that the human contribution to ocean noise has increased during the past few decades: human noise has become the dominant component of marine noise in some regions, and noise is directly correlated with the increasing industrialization of the ocean. Sound is an important factor in the lives of many marine organisms, and theory and increasing observations suggest that human noise could be approaching levels at which negative effects on marine life may be occurring. Certain species already show symptoms of the effects of sound. Although some of these effects are acute and rare, chronic sublethal effects may be more prevalent, but are difficult to measure. We need to identify the thresholds of such effects for different species and be in a position to predict how increasing anthropogenic sound will add to the effects. To achieve such predictive capabilities, the Scientific Committee on Oceanic Research (SCOR) and the Partnership for Observation of the Global Oceans (POGO) are developing an International Quiet Ocean Experiment (IQOE), with the objective of coordinating the international research community to both quantify the ocean soundscape and examine the functional relationship between sound and the viability of key marine organisms. SCOR and POGO will convene an open science meeting to gather community input on the important research, observations, and modeling activities that should be included in IQOE

Spatial distribution of dugongs by acoustic and visual observation in Thailand

March 5-6, 2009, Bangkok, ThailandDugong calls were collected using a towed stereo hydrophone system around Talibong Island and Muk Island in Thailand in January 2008. Standard visual observation was conducted simultaneously to record the dugong distribution. A total of 223 dugong calls and 80 dugongs were detected. Spatial distributions of both of the acoustical and visual detections were analyzed using Iδ-index. The spatial distribution of the visual detections showed almost uniform distribution and that of the acoustical observations showed concentrated distribution (Iδ=0.85 and 3.18, respectively). The number of snapping noises per minute was less in the areas where dugong calls were observed (P < 0.001). It was suggested that dugongs vocalized selectively in less noisy areas

Preliminary estimation of detection rate of dugong acoustical observation

December 15-17, 2007, Royal Phuket City Hotel, Phuket, ThailandDugongs are the only marine mammal that feeds on benthic seagrass. They are found in warm shallow waters of tropical to sub-tropical areas. Many of the dugong populations are close to extinction. We have established a new methodology to record the presence of dugongs by a passive acoustic monitoring technique using automatic underwater sound monitoring systems for dugongs in the southern part of Talibong Island, Trang, Thailand. This study described the preliminary estimation of detection rate of the dugong acoustical observation system. Visual and acoustical observation was performed simultaneously to compare the detections by each method. The results showed that almost 30% of the dugongs in the monitored area were acoustically detected. It was in the spring tide era when the maximum number of detections was obtained

Monitoring dugong feeding behavior in a tidal flat by visual and acoustic observation

Organized by Graduate School of Informatics, Kyoto University ; JSPS Bangkok Liaison Office ; Japanese Society of Bio-logging Science ; Informatics Research Center for Development of Knowledge Society InfrastructureDecember 13-14, 2005, Siam City Hotel, Bangkok, ThailandDugongs (Dugong dugon) are herbivorous marine mammals and an endangered species. Unfortunately, the lack of basic research especially on the use of seagrass patches by dugongs prevents us from taking any effective countermeasures for their conservation. In this study, to monitor the feeding behavior of dugongs in the seagrass bed of a tidal flat, we conducted automatic visual observation and passive acoustic observation using a digital camera and automatic underwater sound monitoring systems for Dugong (AUSOMS-D). These observation methods were tested around Talibong Island, Trang Province, Thailand. The increase in the number of dugong feeding trails was observed by the automatic visual observation. Dugong feeding sounds were observed by the passive acoustic observation. In this study, the term of dugongs feeding in this site was identified by automatic visual observation, and in addition, the time of dugongs feeding in this site was identified by the passive acoustic observation. Therefore, we propose to combine these two observations. The visual-acoustic combined observation method is effective in monitoring feeding behavior of dugongs. This method has technical benefits with no impact on either the dugongs or the seagrass beds

Effect of ship sound on the vocal behavior of dugongs

December 13-14, 2006, Siam City Hotel, Bangkok, ThailandEffects of man-made, low-frequency sounds on the behavior of the dugong are discussed in this paper. We developed a monitoring system of power-driven vessel to assess the impact of man-made noise on dugongs. Ship navigation was monitored by questionnaire for boaters and visual observations from an anchored vessel. We used automatic under water sound monitoring systems for dugongs (AUSOMS-D) to record under water sound and to track ship navigations acoustically. The visual observations were performed for a total of 10 hours and 20 minutes and 72 ships were detected. The acoustic monitoring was conducted for over 81 hours and detected 258 ships. Shortest distance between the visual-observation platform and the power-driven vessels ranged from 18 to 500 m or more. We calculated the monitoring range of the system by comparing the result of the visual observation and the acoustic survey. The system detected 51.4 % of noise-making ships within 500 meters from the observation platform, and 78.1 %, 89.5 %, and 100 % within 300, 200, and 100 meters, respectively. The ship navigation showed bimodal occurrence during 6:00-7:00 and during 15:00-17:00. We could position the sound source of ship sounds and draw the pathway of a ship by using AUSOMS-D. Based on this result, we calculated the position fix accuracy of ship sound, which was 17.1±8.71 m. This study provided information on detailed techniques for tracking the noise-making vessels and will lead to tracking the vocalizing animal, such as the dugong

Seasonal characterization of dugong feeding and biomass utilization on selected sites in Talibong Island

December 15-17, 2007, Royal Phuket City Hotel, Phuket, ThailandDugong (Dugong dugon) is an herbivorous marine mammal and feeds almost exclusively on sea grass. Previous observation of the dugong feeding behavior revealed that they feed even at intertidal flats where the sea grass beds are completely exposed in the air during low tide and also at other deeper sites, where the tidal range is about 2-6m. We used a passive acoustic monitoring system to monitor their feeding behavior. Dugongs’ feeding sounds were collected at two feeding grounds at an intertidal flat and a deep site. From the result of the comparison of feeding events during daytime to nighttime, we found dugongs mainly feed during the night (Welch t-test p<0.05). We also collected sea grasses at each feeding ground and compared the species composition of sea grasses and density of sea grass between the two sites. We calculated the feeding efficiency from the density of sea grass before and after dugong’s feeding at each site and compared to them. These comparisons revealed that there was no significant difference in the amount of sea grasses fed upon by dugong between the two feeding grounds

Pattern analyses of the vocal structure of dugong calls

Organized by Graduate School of Informatics, Kyoto University ; JSPS Bangkok Liaison Office ; Japanese Society of Bio-logging Science ; Informatics Research Center for Development of Knowledge Society InfrastructureDecember 13-14, 2005, Siam City Hotel, Bangkok, ThailandDugongs (Dugong dugon) produce different types of vocalization such as chirps, trills, and barks. Previous reports showed that dugongs have two kinds of phonemes : long duration calls (trills) and short duration calls (chirp-squeaks hereinafter called chirps). However, the function of these calls was not revealed. The objective of this study is to classify the vocalization patterns of dugong calls and discuss the functional use of call sequences among a local population of dugongs. We recorded the underwater sound for 120 continuous hours by an automatic underwater sound recording system conducted in the southern part of Talibong Island, Trang, Thailand. We analyzed the underwater sound data sets that were obtained by the system. Call durations differ among local populations. Short duration calls with less than 300 ms were defined as chirps and trills were defined as a call lasting over 300 ms. The end of a call sequence was defined as a silence over 1 second. A total of 1559 audible calls were detected from a total of 15 hours data set (from 3:50 to 6:50 29 February 01-04 March 2004). Chirps were observed more than trill calls (1470 chirps and 89 trills). Chirp-to-chirp transitions were most frequency observed (83.70%), whereas trill-to-trill transitions were the least (3.97%). Transitions between the two types of calls were also observed (6.80%, 5.53%). The stability of the sequence of each type of calls in a call sequence is investigated. The call sequence analysis as well as the behavioral context observation will provide the key to interpret the function of dugong calls