著者
堤 千華 市川 光太郎 赤松 友成 荒井 修亮 新家 富雄 原 武史 カンジャナ アドゥンヤヌコソン
出版者
海洋理工学会
雑誌
Journal of Advanced Marine Science and Technology Society = 海洋理工学会誌 (ISSN:13412752)
巻号頁・発行日
vol.11, no.1, pp.77-80, 2005-10-30
参考文献数
6

Dugongs {Dugong dugon) are herbivorous marine mammals and endangered species. Unfortunately, the lack of basic research especially on use of seagrass patches by dugongs prevents us from taking any effective countermeasures for the conservation.In this study, to monitor feeding behavior of dugongs in the seagrass bed of a tidal flat, we propose a visual-acoustic combined observation method which is comprised of the visual observation and the acoustic observation using a digital camera and automatic underwater sound monitoring systems for dugong (AUSOMS-D). This new observation method was tested in Thai waters. The increase in the number of dugong feeding trails was observed during nighttime by the visual observation. Dugong calls and feeding sounds were recorded by the acoustic observation. The increase of the dugong feeding trails coincided with the feeding sounds. Therefore, the visual-acoustic combined observation method is effective in monitoring feeding behavior of dugongs. This method has technical benefits not to impact both on the dugongs and the seagrass beds.
著者
新家 富雄 江本 博俊 今津 安成 清水 浩 服部 真人
出版者
海洋理工学会
雑誌
Journal of Advanced Marine Science and Technology Society = 海洋理工学会誌 (ISSN:13412752)
巻号頁・発行日
vol.15, no.1, pp.47-54, 2009-11-07
参考文献数
10
被引用文献数
1

Passive acoustic biotelemetry for Dugong dugon enabled us to monitor the presence and the position of dugongs by receiving their calls using underwater sound techniques. The principle of the acoustic biotelemetry is to identify the sound source directions of their calls calculated from the time arrival differences between plural hydrophones. This method requires stereo automatic underwater sound monitoring systems. From 2003 to present, we have been developing the stereo underwater recording system. AUSOMS-D (Automatic Underwater Sound Monitoring System for Dugong). AUSOMS-D records underwater sound of frequency band between 20 Hz to 20 kHz by stereo (2ch) hydrophones at sampling frequency of 44.1 kHz with 16 bits resolution for many days. Progresses of AUSOMS-D have been made such as down sizing of the pressure resistant housing, longer recording time and additional scheduling functions. The latest AUSOMS-D is 7 kg in the air weight. It can record up to 15 days continuously with 16 alkaline D cells. AUSOMS-Dwas applied for the survey of dugong in Thailand's water many times.On the other hand, we have developed a stereo towed hydrophone system. The system is called "Towed Aquafeeler". Towed Aquafeeler can receive underwater sound of frequency band between 100 Hz to 20 kHz by 2ch. Recommended tow speed of the system in listing mode is 6 knots or less. Towed Aquafeeler is 11 kg in the air and neutral buoyancy in the water. It was also used for the dugong surveys in Thailand water twice.
著者
笠原 勉 原 宏江
出版者
海洋理工学会
雑誌
Journal of Advanced Marine Science and Technology Society = 海洋理工学会誌 (ISSN:13412752)
巻号頁・発行日
vol.15, no.1, pp.67-72, 2009-11-07

The Fishery Agency conducted the investigations and researches on the restoration of tropical sea grass beds, which serves as feeding sites for dugongs. from FY 2001 to FY 2008. as a part of its project aiming at the coexistence of dugongs and the fishery. In addition to the results of the project, such as seedling production and transplanting techniques, the existing knowledge and information on the sea grass beds were collected and complied in a booklet. The former part of the booklet " A review for the restoration of tropical sea grass beds" summarizes existing knowledge and information on 1) the component species, functions and roles. 2) habitats and environmental conditions. 3) the distribution area and standing stock and 4) dugongs' biology and the relationship with tropical sea grass beds, while the latter part explains 1) restoration techniques of sea grass beds using hand grass planting. 2) seedling production techniques using Thalassia hemprichii, 3) transplanting techniques of artificially produced Thalassia hemprichii and 4) monitoring of created or restored tropical sea grass beds.
著者
向井 宏
出版者
海洋理工学会
雑誌
Journal of Advanced Marine Science and Technology Society = 海洋理工学会誌 (ISSN:13412752)
巻号頁・発行日
vol.15, no.1, pp.73-87, 2009-11-07
参考文献数
10

Knowledge of feeding ecology which have been studied on reared and wild dugong are described. So far. 15-20 kg (wet wt)/day has been reported as feeding rate of a dugong in Toba aquarium. And, two estimations of feeding rate on wild dugong by author are introduced. Feeding rate of dugong on Halophila ovalis was estimated based on observation of dugong behavior and feeding trails in Khao Bae Na sesagrass bed. Trang, Thailand, and on long term observation of dugong behavior in New Argao seagrass bed. Davao Gulf. Mindanao. Philippines. From these results, it was discussed the possibility that the knowledge of feeding rates have been published was overestimation. Because the estimation have been published was based upon short-term observation. The feeding rate considerably varied seasonally and monthly. Feeding rate per day obviously fluctuated with lunar cycle. Also the rate increased in dry season and decreased in wet season.