Harumi Sugimatsu

Bio: Harumi Sugimatsu is an academic researcher from University of Tokyo. The author has contributed to research in topics: Ganges River Dolphin & Hydrophone. The author has an hindex of 10, co-authored 36 publications receiving 229 citations.

Diel changes in the movement patterns of Ganges River dolphins monitored using stationed stereo acoustic data loggers

Abstract: We monitored the underwater movements of Ganges River dolphins using stationed stereo acoustic data loggers. We estimated these movements using changes in the relative angle of the sound source direction (trajectory). Of the total acoustic recordings (66 h), 26.2% contained trajectories of dolphins, and 78.6% of these trajectories involved single animals, suggesting that dolphins tended to swim alone and were localized near the monitoring station. The observed trajectories were categorized as follows: staying type characterized by small changes in the sound source direction, moving type A (moving in the same direction), and moving type B (moving up and down the stream during recording). The average interpulse intervals of sounds in moving types A and B were significantly shorter than that of the staying type, suggesting that dolphins produce the former types of trajectories to echolocate across shorter distances during movement. The frequency of occurrence of moving type A increased during the night, whereas that of type B increased in the late afternoon and that of the staying type increased during the daytime. These results indicate that dolphins moving at night tended to use short-range echolocation, whereas during the day, they remained in relatively small areas and used long-range sonar.

Localization of sperm whales in a group using clicks received at two separated short baseline arrays.

Abstract: In this paper, a sperm whale click analysis scheme is proposed in order to calculate the position of individual sperm whales in a group using data received at two arrays deployed near the surface. The proposed method mainly consists of two parts: short baseline (SBL) with classification and long baseline (LBL) with class matching. In SBL with classification, a click is automatically detected, and its direction of arrival is calculated. The clicks are then classified based on their direction vectors. The class data are then sent together with direction data and matched to the other array’s class data. LBL with class matching is used for localization. The classification algorithm can be used to estimate the number of whales clicking and to list potential candidates for LBL matching. As a result, the proposed method is able to localize the positions of the whales in a group. The performance of the proposed method is evaluated using data recorded off Ogasawara islands with two arrays near the surface. The three-dimensional underwater trajectories of six sperm whales are extracted to demonstrate the capability of the proposed method.

Underwater behavioral study of Ganges river dolphins by using echolocation clicks recorded by 6-hydrophone array system

Abstract: Targeting the 9 Ganges river dolphins inhabiting the Narora area in Ganges river system, the first recordings using an compact acoustic observation system, which consists of a high frequency 6-hydorophone cross array connected with a PC on land-base by a wireless LAN system have been carried out during 17 to 21 February 2008. The system also uses the prototype of a GPRS modem-based real-time data transmission system to share the processed data with the world over the internet. The array structure consists of a horizontal cross array formed by 2 arms each of 1.6 meter length with a hydrophone on each corner and at the intersection forming two equi-spaced 3-hydrophone linear SBL system for omni-directional horizontal coverage, and one additional hydrophone which is fixed 0.8 meter below the center hydrophone of the cross array also forming an equi-spaced triangular SBL system for vertical measurement. The clicks of the dolphins received on each hydrophone were sampled at a rate of 500 kHz per channel. Total recording was done for approximately 40 hours due to power supply interruptions. However, the GPRS modem-based real-time data transmission system worked well during the recordings. The results of the basic analysis of the data show that the dolphins are found swimming up and down the river. The results are in accordance with the visual observation results. Underwater behavior of the dolphins approaching near to the array, which could not otherwise have been observed by visual survey, has been mainly analyzed in this paper. Based on ICI during this period of approaching to the array, we estimated ldquowhat this dolphin is seeingrdquo or interested in. We invoked the idea of lag time that the dolphin requires to perform echo-location process and to emit the next click to the target [7]. Defining the lag time as DeltaP (pre-click time) and assuming that DeltaP is constant, DeltaP and distance D to the target where the dolphin is looking at is calculated by using ICI and range between the dolphin and the array, which is measured by the array. Utilizing available on-axis clicks from the data of the preliminary experiments in Budhabalanga river, the value of DeltaP is calculated. Constant DeltaP is estimated as 14.3 milliseconds. To determine D of the Narora data, we applied it when the dolphin was approaching to the array within 20 meters. The results show that the dolphin does not look at any object beyond 20 meters range. On the other hand, when ICI reduced below the constant DeltaP (14.3 milliseconds) , it is estimated that the dolphin is in a different stage of the echo-location process.

Acoustic Survey Of Irrawaddy Dolphin Populations In Chilika Lagoon: First Test Of A Compact High-Resolution Device

Abstract: Irrawaddy dolphins (Orcaella brevirostris) being on top of the food chain are considered as a flagship species of Chilika. These cetaceans produce characteristic echolocation pulses that make them acoustically visible, night or day. Acoustic-based survey methods are found to be indispensable for surveying porpoises and dolphins in coastal precincts. This paper reports the first such collaborative attempt in Chilika by applying acoustic survey technology based on the design of an innovative compact and portable acoustic survey device designed for observation of groups of small cetaceans. The acoustic sensor system is housed in a "bird-cage" structure containing 3 hydrophones forming a main linear array, together with two more hydrophones forming a small 3-element triangle array with the central hydrophone, in a plane perpendicular to the linear array axis. It weighs 25 kg and is 3.6 m long, 30 cm in diameter, and can be deployed either vertically or horizontally with buoys and a weight. A high-speed multichannel data acquisition system records the dolphin click sounds from all hydrophones. Signal processing algorithms have been developed for automatic detection and discrimination of echolocation clicks from other underwater sounds, localization of sound sources, and tracking individual animals. The device has previously been tested in vertical mode in a quasi-natural environment with a group of bottlenose dolphins that has confirmed its capability to precisely track several vocalizing animals. The depth of the Chilika lagoon in the dolphin habitat can be as shallow as 1.5 m. Thus, the array has to be deployed in horizontal mode, which enables it to provide very good lateral resolution in the broadside direction. This paper reports the first results of using this array in shallow water conditions. Movements of several Irrawaddy dolphins have been observed very clearly.

Beam pattern estimation of clicks of a free-ranging Ganges river dolphin

Abstract: The first recordings of bio-sonar clicks of free-ranging Ganges river dolphin (Platanista gangetica) were made in Budhabalanga river in Orissa, India. The system used for recording is a 3.2 meter long array composed of three hydrophones forming an equispaced linear SBL array and another two hydrophones in conjunction with the central hydrophone forming a small SSBL triangular array in a plane perpendicular to the array axis. The array structure was deployed both in horizontal and vertical configurations. The clicks of the dolphin received on each hydrophone were sampled at a rate of 500 kHz per channel. From the sampled clicks data, the sonar transmit beam pattern of the dolphin in both horizontal and vertical plane was estimated using difference of ASL (apparent source level of the click signal) and the absolute angles of the dolphin's location between the central hydrophone and the other two peripheral hydrophones for the on-axis clicks. To estimate more accurate beam pattern, conditions for selection of on-axis clicks were well-considered, and thus we propose a new criteria for determining on-axis clicks. In this method, we assume that the dolphin's beam pointing direction is towards the central hydrophone and it's beam pattern is symmetrical. However, actual measurement of ASL from three hydrophones shows that values at the peripheral hydrophones are not always same. This suggests that the dolphin's beam is not pointing exactly towards the central hydrophone so that the central hydrophone's ASL is not the real peak value of the beam. We propose a refinement in the beam pattern estimation method using interpolation and curve fitting to obtain an improved estimate of the Ganges river dolphin's beam pattern. By analyzing all available clicks, we have estimated the dolphin's beam pattern in both horizontal and vertical plane. The 3-dB beamwidth is found to be approximately 10 degrees in horizontal plane and 14 degrees in vertical plane. In this paper, we propose the new beam pattern estimation method using interpolation and curve fitting.

Clicking in Shallow Rivers: Short-Range Echolocation of Irrawaddy and Ganges River Dolphins in a Shallow, Acoustically Complex Habitat

Abstract: Toothed whales (Cetacea, odontoceti) use biosonar to navigate their environment and to find and catch prey. All studied toothed whale species have evolved highly directional, high-amplitude ultrasonic clicks suited for long-range echolocation of prey in open water. Little is known about the biosonar signals of toothed whale species inhabiting freshwater habitats such as endangered river dolphins. To address the evolutionary pressures shaping the echolocation signal parameters of non-marine toothed whales, we investigated the biosonar source parameters of Ganges river dolphins (Platanista gangetica gangetica) and Irrawaddy dolphins (Orcaella brevirostris) within the river systems of the Sundarban mangrove forest. Both Ganges and Irrawaddy dolphins produced echolocation clicks with a high repetition rate and low source level compared to marine species. Irrawaddy dolphins, inhabiting coastal and riverine habitats, produced a mean source level of 195 dB (max 203 dB) re 1 µPapp whereas Ganges river dolphins, living exclusively upriver, produced a mean source level of 184 dB (max 191) re 1 µPapp. These source levels are 1–2 orders of magnitude lower than those of similar sized marine delphinids and may reflect an adaptation to a shallow, acoustically complex freshwater habitat with high reverberation and acoustic clutter. The centroid frequency of Ganges river dolphin clicks are an octave lower than predicted from scaling, but with an estimated beamwidth comparable to that of porpoises. The unique bony maxillary crests found in the Platanista forehead may help achieve a higher directionality than expected using clicks nearly an octave lower than similar sized odontocetes.

Methane, manganese, and helium-3 in newly discovered hydrothermal plumes over the Central Indian Ridge, 18°–20°S

Abstract: We have investigated newly discovered submarine hydrothermal plumes over the Central Indian Ridge, 18°–20°S Onshore chemical analyses of methane, its carbon isotope, manganese, and helium-3 in seawater samples obtained from the plumes revealed their detailed geochemical characteristics One of the newly discovered hydrothermal plumes located over the western wall of the axial valley at Segment 15B (19°33′S), called the Roger Plateau, showed constant CH4/Mn and CH4/3He ratios throughout the plume The CH4/3He ratio (4 × 106) and δ13C (−175‰) are consistent with those of basalt-hosted sediment-free hydrothermal systems, although the CH4/Mn ratio (∼1) is moderately higher These features are thought to indicate a metal-depleted fluid chemistry The other hydrothermal field is located within the axial valley at the northern part of the smooth lava plain at Segment 16 (18°20′S), called the Dodo Great Lava Plain, where several plumes were detected The CH4/Mn and CH4/3He ratios showed large variation through the plumes while δ13C values were almost constant Geochemical characteristics of venting fluid estimated from those of the plumes were apparently high CH4/Mn (>6) and CH4/3He (>60 × 106) ratios and low δ13C values (<−275‰), suggesting possible influences of several methane input processes to the fluid chemistry

Trends in tagging of marine mammals : a review of marine mammal biologging studies

Abstract: An Alexander von Humboldt Foundation Fellowship, as well as a research fellowship from the University of Pretoria.

AUV "TUNA-SAND" and its Exploration of hydrothermal vents at Kagoshima Bay

Abstract: In this paper, we introduce a newly developed AUV (Autonomous underwater vehicle) "TUNA-SAND"(Terrain- based Underwater Navigable AUV for Seafloor And Natural resources Development) and its exploration of the hydrothermal vent in Kagoshima Bay, Japan carried out on August 2007. TUNA-SAND is a hovering type AUV constructed in March 2007 as a platform for visual investigation of seafloor features.