Aquariums globally have seen significant growth in recent decades. However, persistent negligence exists concerning underwater sound pollution in aquariums and its impact on cetaceans. Here, the audiogram of Taotao, the world's first successfully captive-born and bred Yangtze finless porpoise, and the underwater sound levels in the Baiji Aquarium at the Institute of Hydrobiology, Chinese Academy of Sciences were examined. In contrast to the previously published U-shaped audiograms of the Yangtze finless porpoise, Taotao's audiogram exhibited a W-shaped pattern. Additionally, the audiogram of Taotao was, on average, 42 ± 15 dB (mean ± SD) higher than that of other non-aquarium-born Yangtze finless porpoises in the Baiji Aquarium and 43 ± 11 dB higher than that of wild Yangtze finless porpoises, particularly in the 20-60 kHz range and at 90 kHz. The underwater sound spectra in the Baiji Aquarium do not account for the notches observed in the porpoise's audiogram below 60 kHz, suggesting that congenital hearing disorders may be the cause of Taotao's hearing loss in these frequency bands. In contrast, the cumulative weighted broadband sound exposure levels of underwater sound within the aquarium (mean: 162 dB) exceeded the temporary threshold shift onset threshold for non-impulsive noise (153 dB) and the permanent threshold shift onset threshold for impulsive noise (155 dB) in finless porpoises. The high levels of underwater sound exposure, particularly from conspecific porpoises, highlight the need for increased focus on the welfare of captive animals.

Numerous dams disrupt freshwater animals. The uppermost population of the critically endangered Yangtze finless porpoise has been newly formed below the Gezhouba Dam, however, information regarding the local porpoise is scarce. Passive acoustic monitoring was used to detect the behaviors of porpoises below the Gezhouba Dam. The influence of shipping, pandemic lockdown, hydrological regime, and light intensity on the biosonar activity of dolphins was also examined using Generalized linear models. Over the course of 4 years (2019-2022), approximately 848, 596, and 676 effective monitoring days were investigated at the three sites, from upstream to downstream. Observations revealed significant spatio-temporal biosonar activity. Proportion of days that are porpoise positive were 73%, 54%, and 61%, while porpoise buzz signals accounted for 78.49%, 62.35%, and 81.30% of all porpoise biosonar at the three stations. The biosonar activity of porpoises was much higher at the confluence area, particularly at the MZ site, during the absence of boat traffic, and during the Pandemic shutdown. Temporal trends of monthly, seasonal, and yearly variation were also visible, with the highest number of porpoises biosonar detected in the summer season and in 2020. Significant correlations also exist between the hydrological regime and light intensity and porpoise activity, with much higher detections during nighttime and full moon periods. Hydropower cascade development, establishment of a natural reserve, fish release initiatives, and implementation of fishing restrictions may facilitate the proliferation of the porpoise population downstream of the Gezhouba Dam within the Yichang section of the Yangtze River. Prioritizing restoration designs that match natural flow regimes, optimize boat traffic, and reduce noise pollution is crucial for promoting the conservation of the local porpoises.

Acoustic properties of the underwater environment are important in maintaining biological processes of various marine organisms. However, with the increasing level of underwater noise in the global ocean, there is a growing need to better understand how marine animals use soundscape cues in their habitat selection. Indo-Pacific humpback dolphins (Sousa chinensis) inhabiting the Pearl River Estuary, southeast China, live in one of world's most developed and noisiest coastal environment and are subjected to many sources of anthropogenic noise. To investigate whether spatial variability of underwater soundscape corresponds with their habitat utilization, we collected daytime underwater recordings in western Hong Kong waters from mid-2016 to mid-2018, and quantified the spatial pattern of marine acoustic environment and its differing characteristics in a fine spatial scale. We developed a framework of soundscape information retrieval to investigate spectral features that may facilitate identification of dolphins’ core habitats. Our findings reveal that a spectral feature, which peaks at 2 kHz, is a reliable predictor of humpback dolphin core habitat. Further modelling of spatial and seasonal variations of underwater soundscape demonstrates that the relative strength of this spectral feature is positively correlated with the sighting rates of humpback dolphins throughout the year. Although the source of the 2 kHz feature remains unknown, it is likely associated with humpback dolphins’ prey. We suggest that underwater acoustic environment represents an important component in evaluating the quality and suitability of coastal habitats for the daily needs of this threatened dolphin species. Local and regional conservation authorities should include habitat-specific baseline soundscape data when developing conservation management strategies.

Examining the spatiotemporal habitat use by marine megafauna and human activities at a fine scale is important to achieve harmonised management of coastal areas. Passive acoustic monitoring (PAM) can provide this information by observing animal vocalisations and the sounds generated by motorised vessels. Dugongs (Dugong dugon), which are endangered herbivorous mammals inhabiting coastal seas, communicate through social calls. Although their spatiotemporal acoustic presence on a fine scale could assist in prioritizing local marine spatial planning, such knowledge is limited. To address this gap, we examined the spatiotemporal pattern of the acoustic presence of dugongs and its correlation with environmental and anthropological factors; additionally, the overlap of these areas with vessel traffic was illustrated. Underwater recorders were deployed at 11 locations around Talibong Island, Thailand, for one month in both rainy and dry seasons. Based on the recorded sound stream, dugong calls and vessel sounds were automatically detected using custom-made software, and false detections were removed by manual examinations. In 2019 and 2020, 1933 h and 2719 h of recordings, respectively, revealed that while dugongs had a clear spatial preference for vocal communication at some locations, their temporal patterns varied among locations. Further, their acoustic presence was significantly correlated with environmental and anthropological factors at some locations, while these factors varied among other locations. However, the distribution of vessel traffic was spatially and temporally stable. These results suggested that (1) spatial management of vocalisation areas can effectively conserve dugongs by protecting their social behaviour and (2) temporal planning may reduce the potential disturbance risk to dugongs. Moreover, to achieve harmonised marine spatial planning in coastal areas, the PAM approach for social calls can be effectively employed to provide a unique layer of habitat use for vocalising species and vessel traffic on a fine scale.

Research on evidence-based marine policymaking is still immature, especially regarding the utilization of text data. This study visualized the transition of ocean policy in Japan using text mining technique applied to the text data of three annual reports: the Fishery white paper from 2007 to 2020, Environmental white paper from 2008 to 2020, and Ocean white paper from 2004 to 2020. The results of the analysis were compared with the expert interviews on each subject. Based on latent Dirichlet allocation (LDA) topic model analysis, significant differences in topics were observed among these white papers, while they all clearly responded to the Great East Japan Earthquake occurred in 2011 with their unique topics. Major transitions in topics occurred several times over the years for all white papers. For the Fishery white paper and Environmental white paper issued by the government agencies, notable transitions occurred in 2011, 2013, 2017 and 2012, 2018, respectively, which were mainly caused by the revisions of relevant laws; while for the Ocean white paper issued by non-government organization, transitions occurred in 2009 and 2016, which were closely related to the development of worldwide ocean initiatives. The expert interviews revealed that the experts’ views on the topics and the transitions of policy focuses were generally consistent with the unsupervised analysis results. Automated visualization of policy transition in each organization accelerates the extraction of their directions and roles in policymaking which will help provide scientific evidence for identifying future opportunities for inter-organizational collaboration.

Within the set of risk factors that compromise the conservation of marine biodiversity, one of the least understood concerns is the noise produced by human operations at sea and from land. Many aspects of how noise and other forms of energy may impact the natural balance of the oceans are still unstudied. Substantial attention has been devoted in the last decades to determine the sensitivity to noise of marine mammals—especially cetaceans and pinnipeds—and fish because they are known to possess hearing organs. Recent studies have revealed that a wide diversity of invertebrates are also sensitive to sounds, especially via sensory organs whose original function is to allow maintaining equilibrium in the water column and to sense gravity. Marine invertebrates not only represent the largest proportion of marine biomass and are indicators of ocean health but many species also have important socio-economic values. This review presents the current scientific knowledge on invertebrate bioacoustics (sound production, reception, sensitivity), as well as on how marine invertebrates are affected by anthropogenic noises. It also critically revisits the literature to identify gaps that will frame future research investigating the tolerance to noise of marine ecosystems.

Sound propagates at a greater range than light in marine environments. Anthropogenic sound and noise pollution caused by deep sea mining and offshore wind farms are increasing, which may affect the marine ecosystem. However, sound datasets in oceanic environments are quite limited. In this paper, we summarize the requirements of a deep sea soundscape monitoring device by reviewing currently available instruments, and we propose a cost-effective and noise reductive recording system to the monitor marine soundscape to identify temporal variations in the soundscape at various scales. The development of this system is ongoing, and we summarize the results of two trial deployments in a huge aquarium tank and off the pier of a marine station. The results demonstrate that the noise generated and the battery consumption of the proposed system are comparable to conventional systems. However, the proposed system is highly versatile due to the scalability of the IDE of the system's software. Our work to develop a cost-effective, noise-reductant and long-term recording system will contribute to the acquisition of soundscape data in marine environments, which is expected to enable the identification of baseline sound properties in various marine environments and reconstruct temporal and spatial variations of marine biodiversity and ecosystem dynamics.

group have developed an underwater sound recording device capable of observing underwater sound for approximately one year at a depth of 6,000 meters. We installed this device on the underwater explorer "Edokko Mark I (Type 365),"and obtained intermittent recording for about one year at the research station LE4, located about 160 km offshore south of Minami-Torishima Island, Japan, where marine mineral resources exist. In this study, we report on the newly developed underwater sound recording device and the results of the soundscape analysis.

Passive acoustic monitoring (PAM) has been introduced to monitor rockfish populations and distributions. We conducted water tank experiments to determine whether the white-edged rockfish (Sebastes taczanowskii) is soniferous and to confirm whether its sound properties are appropriate to adopt the PAM method. We observed two types of sound production by white-edged rockfish. The pulse durations of the Type 1 and Type 2 sounds were 0.017±0.003 s and 0.071±0.034 s, respectively, and their peak frequencies were 456.0±54.9 Hz and 116.3±28.1 Hz. These results suggest that white-edged rockfish produce sounds specific to their species and that it would therefore be possible to estimate the fish population by PAM.

Coral reefs represent the most biologically diverse marine ecosystem, however, they are vulnerable to environmental changes and impacts. Therefore, information on the variability of environment and biodiversity is essential for the conservation management of coral reefs. In this study, a soundscape analysis based on range-wide and long-term underwater recording were conducted. Maps of damselfishes and snapping sounds could be obtained by supervised feature extraction of species specific sounds. Using unsupervised classifier, Shannon index of soundscape diversity was shown to be high in deep waters. Mesophotic coral reefs in deep water have been considered as potential refuges for symbiotic corals when coral bleaching happens in shallow reefs due to high sea surface temperature. Results seemed to be consistent with this hypothesis.

Ice-breeding seals use vocal communication mainly during breeding season. The vocal function of aquatic mating, ice-associated ribbon seals (Histriophoca fasciata) has been unknown since they produce sounds in both breeding and non-breeding seasons. We examined the timing of their vocal presence in relation to environmental factors to infer the function of their calls in the Nemuro Strait, northern Japan, since this area is the possible southern limit of their breeding range. Vocalizations of ribbon seals were irregularly sampled from November 2012 to March 2014 in the Nemuro Strait and were compared with sea ice presence, time of day, and tidal currents. Ribbon seal downsweeps were detected in February 2013 and March 2014 only when sea ice was present along the Shiretoko Peninsula in the strait, with more detections in March leading up to the spring breeding season. Downsweep detections decreased in the middle of the day, indicating that ribbon seals were likely to be hauled out during this time. Vocalizing at night and early morning would probably reflect the increased opportunity for attracting females underwater. Our study suggests that the seal vocalizations in concurrence with sea ice presence in the Nemuro Strait could function as underwater communication for breeding.

<p>We observed the sound production and properties of fox jacopever (<i>Sebastes vulpes</i>) in a water tank experiment to obtain basic information for the Passive Acoustic Monitoring (PAM). Six pairs of experiments including mature and immature fishes were conducted, and sound properties with and without agonistic behavior were compared. Fox jacopever produced low frequency pulses under 2,000 Hz. Pulse number ranged between 1–77, pulse duration was 0.005–0.220 s, pulse period was 0.001–0.989 s, and peak frequency was 258–490 Hz. These properties were changed by the presence or absence of agonistic behavior. Higher peak frequency over 400 Hz was observed only when a pair included an immature fish. Our results showed the potential use of fish sounds for estimating size and status of territorial behavior in this species by PAM.</p>

Many kinds of fish, including croaker, produce species-specific low-frequency sounds associated with courtship and spawning. A recording system was used to monitor underwater fish call sounds. A method was previously proposed to detect croaker calls from data measured by a single hydrophone (channel). However, it was difficult to detect the desired calls at a high detection rate because of a low signal-to-noise ratio and overlapping of calls. In this manuscript, we propose a new method using beamforming to improve the detection rate. The proposed method uses four-channel data recorded by two stereo recorders. First, calls are detected from data measured on one channel(ch1) using the previous method, which detects calls automatically using the acoustic features of fish calls such as duration and periodicity. Next, additional calls are detected by beamforming the four-channel data. The detection rate using the proposed beamforming method was higher than that under the previous method with a single data channel, indicating that the proposed method is able to monitor sounds from croaker in the ocean.

The noise evaluation of the platform is necessary to use passive acoustic monitoring. In this study, we measured background noise of underwater platforms such as AUVs and deep sea landers. AUV that has thrusters was higher background noise level, when control own position and speed. However, background noise level was deduced, when stopped thrusters. The background noise of AUV of the type of control buoyance of own and of the deep sea lander was low. The background noise of AUVs on low frequency range was higher than high frequency range. A biological sound was observed using AUV. Even if AUV was to depth of the water 900m, the sound of the creature was measured. Therefore, the biological sound could be observed using AUVs or the deep sea lander, and the possibility that the biological sound could be observed automatically and extensively was indicated.

Presence of finless porpoises around Kansai International airport was monitored by a passive acoustic monitoring system. The airport is an artificial land in the ocean and was suggested to create new habitat of marine organisms. Here we showed frequent nocturnal presence of finless porpoises at the south west of the airport where quite limited visual observation data available previously. During 4 months period from December to April in 2016, biosonar sounds of finless porpoises were detected nearly every day. Accumulated number of click trains in one hour time bin were 100 or larger in the nighttime. In contrast, approximately 50 click trains were recorded in the daytime. Ocean engineering newly created an island, Kansai International airport. This structure might create new habitat even for top predators in this water.

A previous research reported that the cable system off Kushiro-Tokachi was detected low frequency calls of fin whales. In this research, as an application using cable observatories about 'development of remote species identification technologies for marine organisms', we developed a real-time processing system for underwater acoustic signal with cable observatory. This paper reports the results of automatically detection and localization from continues observation using hydrophones and seismometers of the cable observatory. The applied system in cable observatories visualizes the number and position of fin whales.

Many animals in the ocean produce sounds for mating choice, territorial defending, group cohesion and echolocation. Sound travels much longer distance in the water comparing with light that makes the acoustic waves efficient for long distance communication and sensing. The species or family specific sounds can be used to identify not only the presence of animals but also counting the number and density of target species. In these years, various types of underwater recorders are available. However, for the successful acoustic monitoring in the ocean, safe platforms to deploy the recorders are essential. In this paper, advantages and drawbacks of fixed and mobile platforms for passive acoustic monitoring are summarized referring practical application examples in Japanese waters.

In this research, the automatically analyzation method which detect acoustic events such as fin whale calls and its locations is embedded in cable observatory system. This system has detection method about fin whale calls using spectrogram correlation, and the localization of fin whale calls using two hydrophones and a three-axis seismometer. This observation at off Kushiro-Tokachi has been continuously performed for more than 10 years. The detection and tracking analysis for fin whale calls are carried out about the archive data in parallel with the real-time data. The results of the past 10 years including the latest information is reported.

<title>Abstract</title>
Fin whales (Balaenoptera physalus) undergo seasonal migration in the Arctic Sea. Because their migration and distribution is likely affected by changes in global climate, we aimed to examine the migration timing of fin whales, and the relationship with prey availability within the oceanographic environment of the Arctic Sea, using passive and active acoustic monitoring methods. Automatic Underwater Sound Monitoring Systems were deployed in the southern Chukchi Sea from July 2012 to 2014 to determine the acoustic presence of fin whales. Furthermore, water temperature and salinity were recorded by a fixed data logger. An Acoustic Zooplankton Fish Profiler was additionally deployed to estimate prey abundance through backscattering strength. Sea ice concentrations were obtained by remote sensing data. Fin whale calls were automatically detected using a custom-made software, and the per cent of half-hours containing calls were counted. Fin whale calls were detected from 4 August to 20 October 2012 (78 d) and 25 July to 1 November 2013 (100 d). The extended period of acoustic presence of fin whales during 2013 when compared with 2012 is likely related to a longer ice-free period during 2013. Furthermore, generalized linear model analyses showed that half-hour periods containing calls increased with a rise in water temperature and zooplankton abundance during the initial call presence period, while they decreased with a decrease in water temperature and salinity during the end of the call presence period. Our results suggest that the rise in water temperature and zooplankton abundance affect the timing of migration of fin whales in a way that is consistent with the expansion of their suitable habitats and the extension of their presence in the Arctic Sea.

This study tried to determine robust detection criteria for the croaker's pulse-structure sound, using field recordings in WAV, WMA, and MP3 formats. Acoustic analysis results identified four temporal parameters and one frequency parameter as sound features. These feature quantities depended on the season of the year, not the file format. We created an automatic filter for croaker-sound detection using fixed-width ranges of these five parameters, and automatically detected sounds from identical fish-sound files, or the same files with noise. We also examined the correct detection (CD) and false alarm (FA) rates of the automatic detection. Without any noise mixing, it showed fair performance, e.g., 0% FA. Once noise was mixed, however, the CD reduced in accordance with the signal-to-noise ratio. However, the FA level remained constant (no more than 4.5%).

Passive acoustic monitoring (PAM) has been widely used as the standard method to observe small cetaceans. Recent drastic improvement of monitoring device makes PAM more convenient, cost-effective monitoring method. Also, improvement of analysis methods of acoustic data enables us to estimate habitat range, density, behavior of animals using PAM. However, most previous studies focus on one species and select the data that the observed species were confirmed visually. In order to extend the application of PAM to the field that several species appear simultaneously, species identification method is essential. Especially, PAM plays a key role of environmental assessment on marine development such as offshore wind farm in recent years. In that case, it is important to observe each species which appear in the construction area separately for effective conservation. This paper reviewed the recently developed species identification methods. Basically, many identification methods focused on one of two types of animal call, whistles used for communications or biosonar signals used for echolocation. We introduce the advantage and disadvantage of the method using whistles or biosonar signals, and discuss the current issues and future works we need to resolve them.

Environmental changes are considered to affect the migration and distribution of baleen whales in the Arctic region. We examined the seasonal acoustic presence of fin whales (Balaenoptera physalus) and the relationships between acoustics and oceanographic environments in the southern Chukchi Sea from July 2012 to October 2015. Fin whale calls were detected from 4 August to 20 October 2012, from 25 July to 1 November 2013, from 26 July to 14 November 2014, and 7 June 2015, only in the ice-free (sea ice concentration = 0%) periods. In addition, from the recordings in 2012 and 2013, fin whale calls were present in the periods of high prey abundance, and there were significant positive correlations among their call presence, prey abundance, water temperature and salinity. Furthermore, the result that the calls were detected in 7 June 2015 suggests that fin whales arrive much earlier at the southern Chukchi Sea than previously reported. Our study provide valuable information to assess the impact on marine ecosystem in the Arctic region by environmental changes.

It is important information to measure fish movement, swimming direction, and target strength of the fish for species identification by using active acoustics. Broadband quantitative echo sounders have been developed in the world. Broadband system can measure single echo traces from individual fish with high range resolution. Single echo traces with high range resolution give us much more information of fish movements than by using conventional narrow band quantitative echo sounders. This paper presents the results of our in situ measurements.

Freshwater cetaceans are among the data deficient and now recognized as the most threatened group of marine mammals. Large scale studies are required to be done on an urgent basis to ensure reasonable chance of survival for these species. A detailed analysis of the freshwater habitats globally, indicate tropical shallow environment (important for the survival of the freshwater cetaceans). Visual surveys being employed for abundance estimates have significant limitations and acoustic surveys have recently been identified as effective alternative and could complement the visual surveys for conservation efforts. However, two major issues can be prominent such as shallow water sound propagation and noise pollutions. It is well known that shallow waters result in multiple interaction of the acoustic signal with the surface and the bottom prior to being received at the hydrophone receiver. The tropical waters further cause random surface and bottom behaviour resulting in substantial site specific underwater channel fluctuations being coupled to the desired marine mammal signal. Thus, the acoustic survey efforts in the tropical shallow habitats are highly sensitive to the local conditions and demand efforts to mitigate the underwater channel fluctuations while pursuing analysis efforts on the received signal. Increasing population in these regions has resulted in unregulated waterborne activities linked to economic growth. Such activities have caused significant increase in the ambient noise in these habitats. The effectiveness of acoustic sensors is further limited by the high ambient noise in the habitat and could also impact survival chances of these critically endangered species. This work attempts to put in perspective the challenges of acoustic surveys in tropical shallow habitats and provide a way ahead for effective passive acoustic monitoring of the freshwater cetaceans globally.

It is very important to recognise marine biodiversity and to maintain sound ocean ecosystems for long-term and continuous utilisation of the ecosystems services. To ensure this end, ocean environment and ecosystem should be monitored over the long term and a wide range of ocean areas. The purpose of this research is a feasibility study of underwater acoustic observations of marine mammals using a passive acoustic data logger, A-tag. Final goal of this research is to realise the long-term and wide-range monitoring of ocean ecosystems using autonomous underwater gliders, and to evaluate the soundness of ocean ecosystems and environments. This paper deals with underwater acoustic observations of killer whales (Orcinus orca) and analyses of their vocalisation. Underwater passive acoustic observations were conducted at the Prince William Sound, Alaska, USA in the summer of 2013. Direction of vocalisation source was analysed from the time arrival difference between two hydrophones of A-tag. It was demonstrated that the result of acoustic observations of killer whales' vocalisations agreed well with their actual behaviours by visual observations.

Commerson's dolphin (Cephalorhynchus commersonii), one of the smallest dolphin species, has been reported to produce only narrow-band high-frequency (NBHF) clicks and no whistles. To clarify their sound repertoire and examine the function of each type, we analysed the sounds and behaviour of captive Commerson's dolphins in Toba Aquarium, Japan. All recorded sounds were NBHF clicks with peak frequency >110kHz. The recorded click-trains were categorised into four types based on the changing pattern of their Inter-click intervals (ICI): Decreasing type, with continuously decreasing ICI during the last part of the train; Increasing type, with continuously increasing ICI during the last part; Fluctuating type, with fluctuating ICI; and Burst-pulse type, with very short and constant ICI. The frequency of the Decreasing type increased when approaching an object newly introduced to the tank, suggesting that the sound is used for echolocation on approach. The Burst-pulse type suddenly increased in front of the object and was often oriented towards it, suggesting that it was used for echolocation in close proximity to the object. In contrast, the Increasing type was rarely recorded during approach, but increased when a dolphin approached another dolphin. The Increasing and Burst-pulse types also increased when dolphins began social behaviours. These results suggest that some NBHF clicks have functions other than echolocation, such as communication.

The Istanbul Strait (Bosphorus) is a part of the Turkish Straits System, connecting the Aegean Sea and the Black Sea. There are three cetacean species in the Strait, namely the harbour porpoise (Phocoena phocoena), the common dolphin (Delphinus delphis), and the bottlenose dolphin (Tursiops truncatus). To monitor the presence of the cetaceans, a fixed stereo passive acoustic monitoring system (A-tag) was deployed in the middle of the Strait from July 2009 to September 2010. In total 26,814 click trains were detected. Presence, direction and inter-click intervals of phonating cetaceans were measured. Most click trains were detected during the night time. Diel presence pattern was prominent in March and April. In spring, the cetaceans were concentrated in one specific direction from the fixed monitoring system. In contrast, they were found in all directions for the rest of the year. Short range sonar (inter-click intervals (ICIs) less than 50 ms) was commonly detected in spring. During the rest of the year ICIs could reach up to 150 ms. All these findings suggest that they were feeding or socializing in spring and mostly travelling in the other seasons. It is well known that pelagic fish such as sprat and bluefish start their migration from the Aegean Sea to the Black Sea in spring. This study suggests that the cetaceans use the middle part of the Strait for feeding on the pelagic fish in spring when the fish migration has just started. © 2013 Marine Biological Association of the United Kingdom .

Studies of the feeding behaviour of aquatic species in their natural environment are difficult, since direct observations are rarely possible. In this study, a newly developed animal-borne underwater sound recorder (AUSOMS-mini) was applied to captive Amazonian (Trichechus inunguis) and Antillean (Trichechus manatus manatus) manatees in order to directly record their feeding sounds. Different species of aquatic plants were offered to the manatees separately. Feeding sounds were automatically extracted using a custom program developed with MATLAB. Compared to ground truth data, the program correctly detected 65-79% of the feeding events, with a 7.3% or lower false alarm rate, which suggests that this methodology is a useful recorder of manatee feeding events. All manatees foraged during both the daytime and night-time. However, manatees tended to be less active and masticated slower during the night than during the day. The manatee mastication cycle duration depended on plant species and individual. This animal-borne acoustic monitoring system could greatly increase our knowledge of manatee feeding ecology by providing the exact time, duration and number of feeding events, and potentially the plant species being fed on. © 2013 Marine Biological Association of the United Kingdom .

DONET (Dense Ocean-floor Network system for Earthquakes and Tsunamis) is a submarine cabled real-time observation network for earthquakes and tsunamis monitoring around the Nankai trough, southwestern Japan. The scheduled twenty observatories have operated since August 2011. Various sensors such as a broadband seismometer, a pressure gauge, a hydrophone, etc. are equipped with each observatory, because DONET has expected to obtain the data to understand the Nankai trough mega thrust earthquake seismogenic zones. Therefore, in order to supply data stably, it's important to have a method of an investigation of the performance of each sensor in DONET.
In this research, we will evaluate the performance of a hydrophone of DONET. The reference hydrophone was installed several meters from an observatory of DONET. Here, it assumes that both hydrophones will record the acoustic data according to same sound source. And, we will evaluate the performance of a hydrophone by the comparison between reference hydrophone and DONET's one in actual field, and will report the result of the evaluations.

The by-catch of bigeye tuna (Thunnus obesus) has been serious problem for commercial fisheries of skip jack tuna (Katsuwonus pelamis) due to the strong constrain of quarter for each species. Selective catch of skip jack tuna with avoiding by-catch of bigeye tuna is required for sustainable and effective fisheries. Light stimuli were applied in attempts to remove unnecessary tuna species and let them escape through the mesh or underneath of a round net. The movements of fish were observed with coded pingers (passive method) and a broadband quantitative split-beam echo sounder (active method). Newly introduced micro coded pinger (Fusion Inc., Tokyo) for this observation resulted in longer survival or / and retention of tagged fish comparing with previous survey periods. Three hydrophone array systems were deployed on each survey ships (Shoyo-maru, Nippon-maru, and Nippon-maru's boat). The pinger transmitted 31 bits M-sequence signal every 1 second. Movements of multiple tagged fish were able to be observed at the same time. Not only depth change of each fish, but also three dimensional locations could be calculated. In the mean time, schools of fish were observed by the broadband echo sounder near the FADs. The 3D tracks of fishes which were estimated by active way with high distance resolution showed the fish swam deeper at sun rising that was consistent with passive monitoring result. Consequently large data sets of the movement of in situ bigeye tuna and skipjack tuna around FADs were obtained. © 2013 IEEE.

Abundance estimation of marine mammals requires matching of detection of an animal or a group of animals by two independent means. A multimodal detection model using visual and acoustic cues (surfacing and phonation) that enables abundance estimation of dolphins is proposed. The method does not require a specific time window to match the cues of both means for applying mark-recapture method. The proposed model was evaluated using data obtained in field observations of Ganges River dolphins and Irrawaddy dolphins, as examples of dispersed and condensed distributions of animals, respectively. The acoustic detection probability was approximately 80 %, 20 % higher than that of visual detection for both species, regardless of the distribution of the animals in the present study sites. The abundance estimates of Ganges River dolphins and Irrawaddy dolphins fairly agreed with the numbers reported in previous monitoring studies. The single animal detection probability was smaller than that of larger cluster size, as predicted by the model and confirmed by field data. However, dense groups of Irrawaddy dolphins showed difference in cluster sizes observed by visual and acoustic methods. Lower detection probability of single clusters of this species seemed to be caused by the clumped distribution of this species. © 2013 IEEE.

DONET (Dense Ocean-floor Network system for Earthquakes and Tsunamis) is a submarine cabled real-time observation network for earthquakes and tsunamis monitoring around the Nankai trough, southwestern Japan. The scheduled twenty observatories have operated since August 2011. Various sensors such as a broadband seismometer, a pressure gauge, a hydrophone, etc. are equipped with each observatory, because DONET has expected to obtain the data to understand the Nankai trough mega thrust earthquake seismogenic zones. Therefore, in order to supply data stably, it's important to have a method of an investigation of the performance of each sensor in DONET. In this research, we will evaluate the performance of a hydrophone of DONET. The reference hydrophone was installed several meters from an observatory of DONET. Here, it assumes that both hydrophones will record the acoustic data according to same sound source. And, we will evaluate the performance of a hydrophone by the comparison between reference hydrophone and DONET's one in actual field, and will report the result of the evaluations. © 2013 IEEE.

It is required to monitor fish species and amount in order to save marine resources. In the current study, broadband split-beam echo sounder was used to survey fish resources. The echo sounder was useful to track individual fish in schools because individual fish echoes in the schools could be separately measured and three dimensional positions of the echoes could be accurately estimated. It is well known that the acoustic features of fish echoes are closely related to the body length and the apparent tilt angle of a fish. The tilt angle could be estimated by individual tracking. Echoes from fish schools were measured for several hours in the ocean. Echo signals were gathered into one block within a certain depth and a period of time and analyzed to track individual fish in the schools. Target strength was calculated from the individual fish echo and associated with the tilt angle, which was estimated by the individual tracking result. The feature in each block was statistically calculated by averaging target strengths based on the tilt angles. The blocks of the signals were classified by K-means method with the features and divided into some clusters. As a result of the clustering, fish schools in the blocks could be classified. The distribution of the clusters was dependent on both time and depth. © 2013 IEEE.

Responding to the increasing number, size, and speed of commercial ships, the underwater noise is also increasing which could result in a possible adverse impact on marine lives. For clarifying this possible concern, a method for measurement of ship noise and marine lives is required, especially for marine mammals which are sensitive for the frequency range of ship noise. In order to enable to observe marine mammal's behavior and the ship noise simultaneously, this study developed an algorithm to detect ship noise, added to a conventional dolphin detection algorithm. The ship noise is obtained by eliminating some nature sounds and the dolphin's sonar sound. Both dolphin's sounds and ship noises can be separated efficiently so that the noise can be identified using sample data. Further improvement of monitoring system and algorithm are future tasks. © IFAC.

Monitoring fish species and amount with acoustical instruments is a challenging problem to survey fish resources in the ocean. Broadband split-beam echo sounder was useful to observe individual fish behavior in schools. Echoes from fish schools were measured from an anchored vessel for several hours. Echo signals were gathered into one block within a certain depth and a period of time and analyzed to track individual fish in the schools. Target strength was calculated from the individual fish echo and associated with tilt angle which could be estimated by using the tracking result. Feature in each block was statistically calculated by averaging target strengths according to the tilt angles. The blocks of the signals were clustered by K-means method with the features and divided into some clusters. The distribution of the clusters in time and depth was investigated. It appeared that the distributions of the clusters were dependent on both time and depth. Clustering of the features would be effective to monitor diversity of fish in the ocean. © 2013 Acoustical Society of America.

<jats:p>The Amazonian manatee is one of four extant species in the mammalian order Sirenia. They are restricted to the freshwater rivers, lakes and floodplains of the Amazonian river basin where they eat floating and emergent aquatic plants. Visual observation of wild manatees is nearly impossible because of the turbid water and tiny exposure of nose at gentle respiration movement, which consequently precludes study of their underwater behaviour. In this study, we applied animal-worn sound recorder (AUSOMS-mini, System Intec Co., Tokyo, Japan) to two captive Amazonian manatees at INPA, Brazil, in order to record their mastication sounds. Five species of aquatic plants were offered to the manatees separately. Mastication-sounds were extracted by custom made software developed on Matlab for off-line analysis. The mastication intervals and temporal sound structure depended on species of plants. In addition, individual difference of mastication intervals observed in the two manatees was probably due to different body sizes. Overnight recording showed that both manatees kept feeding for more than 0.5 hours followed by 1.6 ± 1.3 hours interruption of feeding. Other sounds such as insect calls, rainfall, and vocalizations of other manatees could be useful to understand habitat selection, weather and presence of conspecifics. Acknowledgment Research and Development Program for New Bio-industry Initiatives</jats:p>

Distribution pattern of dugongs is a key component for space-based managements. Vocal interaction of dugongs may result in a distinctive distribution pattern. This study described the distribution patterns of vocalising dugongs, solitary and cow-calf pairs of dugongs. Total of 31 hours and 24 minutes of aerial surveys over southern Thai waters were conducted to observe distribution of the dugongs in 2006, 2008 and 2010. We also conducted towed acoustic surveys to observe the distribution of vocalising dugongs. Total of 473 adult dugongs and 122 calves and 223 vocalizations were found. The distribution of vocalising dugongs was clumped with the range of about 1 km 2. Groups with cow-calf pairs (9 animals on average) were also clumped. Their distribution range was about 3 km2 and did not overlap that of vocalising dugongs. Average number of individuals in groups without cow-calf pairs was about 1, indicating that the most of the group members were solitary. They distributed widely throughout the focal area with the distribution range of about 41 km2.

The broadband target strength (TS) pattern could be estimated from echoes of the tethered fish by using the broadband signal. This TS pattern was computed by Fourier transform from outputs of cross-correlation function between the emitted signal and echoes from each fish at each tilt angle. Since echoes from fish included multiple reflections, the TS spectra included the interferences among them, as shown in Fig. 4. The degrees of these interferences could be computed by the average of enveloped cepstral patterns at the time, which is larger than 25 microseconds, corresponding to 18 mm along the range axis. As shown in Fig. 5 (b), these degrees were different with four species at the negative tilt angles while these were almost same with them at the positive tilt angles. As shown in Fig.5 (a), it was clarified that averaged TS was changed dependent on fish species and tilt angles.

Accurate estimation of abundance is one of the most important tasks for conservation and management of the endangered species. However, the population estimation of cetaceans in riverine systems is difficult due to the limited cruise course restricted by shallow water and ship lanes. In the present study, we conducted a zigzag survey trial with towed acoustic system in the main stem of the Yangtze River and appended Poyang Lake on the Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), which has been decreasing rapidly in the last couple of decades. The porpoise detected were 4 and 28 individuals per 14 km (by straight-line distance) of the river and lake respectively on the same day. This corresponded to the seasonal site preference of the porpoises reported previously. Eighty-four percent of the porpoises were detected between 100 and 400 m from the bank. We also counted the number of navigating ships, which was 52 and 29 in the same sections of the river and lake respectively. Most of the ships were cargo vessel and navigated in the middle of the river and lake. Although the survey boat had to carefully across the channel, the zigzag transect seemed to be feasible. In the future work, we will examine the persistence to the bank of the porpoises with a bigger data set and should be able to estimate the accurate abundance of the local population.
March 8-9, 2011, BANGKOK, THAILAND

A multi-platform ultrasonic event recorder for towing and stationed monitoring of cetaceans was developed. A stereo acoustic event recorder (A-tag) was originally developed to observe biosonar behavior by tagging on dolphins and porpoises in the wild. In recent years, A-tag has been applied for the acoustic transect to count the number of dolphins and porpoises, and for the long term stationed observation. © 2011 IEEE.

This study showed the preliminary results of two-dimensional localization of echolocating finless porpoises by two stereo acoustic data loggers, A-tags. We conducted passive acoustic observation from an anchored fishing boat using two separated A-tags. Five echolocating porpoises were tracked during a 1.5-hour monitoring. The estimated swimming speeds of the porpoises matched the previous study, which were measured using bio-logging technique. At least one track of porpoises, however, was considered to contain false localization because the swimming speed was faster than the maximum speed of porpoises. Stationary acoustic monitoring has a limited observation range compared to a moving platform. But it has advantages to be able to easily measure the swimming speed and observe under water movement of underwater porpoises. In the future work, it is necessary to observe wild behavior of this species and evaluate the accuracy of the localization method by using larger sample size.
March 5-6, 2009, Bangkok, Thailand

China has various ecologically important sites that provide wonderful research opportunities. The biosonar behavior of Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis) in the semi-natural reserve, Hubei, China has been extensively studied for the past five years by the Japan Fisheries Research Agency and Institute of Hydrobiology, Chinese Academy of Sciences. Careful scanning and acoustical autofocusing behavior in porpoises was firstly observed in free-ranging conditions. The biosonar model obtained in this study allowed us to recently develop a broadband high-resolution sonar system called the Dolphin Sonar Simulator. Frequent biosonar production by finless porpoises also allowed an effective passive acoustical survey to be conducted of the animal along the entire habitat of this species in 2006. Bilateral collaboration with cutting-edge acoustical technologies was proven to be highly productive for basic behavioral science, engineering applications, and the conservation of endangered species. © 2009 The Acoustical Society of Japan.

The population of Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) has been decreasing rapidly in the last couple of decades. One of the large groups of this species is found near the convergent area of Poyang Lake and the Yangtze River. In this study, to monitor and assess the spatial distribution of this local population, the feasibility of towing acoustic survey method combined with visual observation using small boat was examined. During 11-16 May 2007, we conducted acoustic visual combined observations about 20 km per day in the convergent area. A time window of 100 s was employed to define simultaneous detections by both methods. Using the ratio of simultaneous detections, detection probabilities were calculated by the Petersen method as 56 % for acoustics and 24 % for visual detections, respectively. The detection probabilities of this study were higher than previous work. A survey using small boat and short cable to tow the acoustic system was effective to use to monitor local population.
December 15-17, 2007, Royal Phuket City Hotel, Phuket, Thailand

The Yangtze River dolphin or baiji (Lipotes vexillifer), an obligate freshwater odontocete known only from the middle-lower Yangtze River system and neighbouring Qiantang River in eastern China, has long been recognized as one of the world's rarest and most threatened mammal species. The status of the baiji has not been investigated since the late 1990s, when the surviving population was estimated to be as low as 13 individuals. An intensive six-week multi-vessel visual and acoustic survey carried out in November-December 2006, covering the entire historical range of the baiji in the main Yangtze channel, failed to find any evidence that the species survives. We are forced to conclude that the baiji is now likely to be extinct, probably due to unsustainable by-catch in local fisheries. This represents the first global extinction of a large vertebrate for over 50 years, only the fourth disappearance of an entire mammal family since AD 1500, and the first cetacean species to be driven to extinction by human activity. Immediate and extreme measures may be necessary to prevent the extinction of other endangered cetaceans, including the sympatric Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis).

Stationary underwater cameras were deployed to evaluate spatial and temporal distribution of fish assemblage inhabiting a high-rise artificial reef. The camera named FISCHOM has a stereo camera or a monaural camera on board and it can operate periodically by an arbitrary interval. We can acquire the information about fish fauna and fish size distribution and their time series of reef fish assemblages by the assessment using the FISCHOMs. Two surveys were conducted in the early summer and fall of 2005 at a high-rise artificial fish reef in the Sea of Japan. In both surveys, five FISCHOMs were fixed dispersedly on the reef and operated in an hour interval As a result, we could evaluate the spatial and temporal distribution of the fish assemblage and their seasonal variations around the reef about 20 days. In total, 48 thousands of fish were counted in both surveys. Pearl-spot chromis Chromis notata notata, jack mackerel Trachwusjaponkus, and rockfish Sebastes spp. were mainly observed. We confirmed these major species had stable diurnal cycles; they were observed in daytime and rarely observed in midnight The differences of the spatial distributions of the major species were found by comparing the results of each FISCHOMs. The folk lengths of the major species were estimated by stereo measurements. © 2007 IEEE.

Echolocation behaviour of a harbor porpoise and six finless porpoises was recorded in open-water systems using acoustic data loggers (A-tag). In total 1359 click trains were recorded during 4.6 h for the harbor porpoise and 46,240 click trains were recorded during 82.3 h for the finless porpoises. The harbor and finless porpoises produced sonar click trains every 12.3 and 6.4 s on average, respectively. During the inter-click-train interval, the porpoises were silent or produced clicks below 148 dB re. 1 mPa, the detection threshold of the tag. Ninety percent of the inter-click-train intervals were 20 s or less in both species. This means that porpoises frequently produce intense click trains. Click-train intervals lasting over 50 s constituted 1% of the total intervals in finless porpoises and 4% in the harbor porpoise. Both species swam without intense clicks for less than 10m in most cases, but occasionally remained silent or used undetected low-intensity clicks for more than 1 min. During these periods, the porpoises would be susceptible to entanglement in fishing nets.

This paper describes a method and results of measurements of the target strength (TS) spectra of metal spheres and live fish using sonar signals of dolphins with a broadband system. First, we measured the broadband form function of a tungsten carbide and a copper sphere in a water tank and confirmed good agreements with the theoretical values. Second, we measured the TS spectra of three species of anaesthetized fish in a water tank. Although the spectra showed nearly similar tendencies of past measurements, they varied considerably among the species, the individuals, and the tilt angles. Third, we measured the TS spectra of tethered live fish suspended from a ship at the sea. In this case we removed the directivity of transducers by the tungsten carbide sphere suspended near the fish. The sonar signals of dolphin are effective to measure TS spectra of fish.

Dolphins can recognize prey by using the broadband sonar signals. The echo from the fish contains components resulting from multiple reflections, for example, the swimbladder and body surface of the fish. It is necessary for identification of fish species to estimate the positions and amplitudes of these reflections. In this paper, we analyzed the echo from the fish by using the sonar signal of the bottlenose dolphin. Firstly, we analyzed echoes which were measured from the anaesthetized fish in a water tank. It was verified that the numbers and delays of reflections are varied with both the species and the tilt angle. Secondary, we analyzed the echo which was measured from the live fish suspended by nylon monofilament line in the open sea. It was verified that the delays and amplitudes of reflections are varied with the orientation and movement of the fish.

Passive acoustical monitoring systems were used to monitor local migrations of Yangtze finless porpoises in China. We stationed 3 acoustic data loggers (W20-ASII) at 3 different places in the confluence area of Poyang Lake and the Yangtze River on 27-29 April 2006. Acoustic data loggers recorded ultrasonic signals from porpoises swimming in a 300m radius approximate range. Visual observations were conducted simultaneously at two stations. Acoustical and visual observation could detect the presence of porpoises at 73.9 ± 20.9 % and 7.0 ± 6.5 % at all observation times, respectively. Visually-counted group sizes were underestimated compared with acoustical observations for groups of up to 5 individuals, whereas the opposite was true when the group size was more than 6. In summary, a passive acoustical method was proved to be effective for the long term monitoring of finless porpoises swimming underwater. The limitation of group size estimations is thought to be caused by a less accurate measurement of sound source direction due to the short baseline of W20-ASII. It can be improved by employing longer baseline stereo hydrophones.

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 25kg and is 3.6m long, 30cm 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 1.5m. 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. ©2006 IEEE.

Dugongs (Dugong dugon) produce different types of vocalization such as chirp, trill, and barks. Previous reports showed that dugongs have two kinds of phonemes: long duration calls (trill) and short duration calls (chirp-squeaks hereinafter called chirp). Especially, the chirp and trill calls were widely reported in different populations. However, characteristics of call patterns in dugongs have never been reported. Moreover, 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 stability call sequences within and across local populations of dugongs. We recorded the underwater sound at the off Talibong Island, Trang, Thailand in 2004 and 2005 for 120 hours by an automatic underwater sound recording system (AUSOMS-D, System Intech, Tokyo). The AUSOMS-D is the water resistant stand-alone recording system and developed for passive acoustical monitoring targeting human audible range. The AUSOMS-D consisted of a pair of hydrophones located 2 m apart for calculating the bearings of the sound sources. The electric circuits and batteries were housed in a pressure-resistant case, and the hydrophones were connected to a stereo preamplifier. The sound signals were fed into a 1-kHz high pass filter to eliminate low frequency background noise. Digitized signals were recorded on an 80 GB removable hard disk drive by uncompressed format with a time stamp. The power supply system with batteries and DC/DC converter were also housed inside the case. The sampling frequency of the A/D converter was 44.1 kHz and the dynamic range was 74-120 dB (re 1 μPa) with a 16-bit resolution. Each hydrophone had flat frequency responses within 2 dB between 1 and 10 kHz. For the comparison purpose, we made recording of a captive dugong in Toba Aquarium, Japan, which was introduced from Philippine water. We analyzed the underwater sound data set that was obtained in both animals in different environment and populations. Short duration calls with less than 300 milliseconds were defined as chirp and trill was defined as a call lasting over 300 milliseconds. The end of a call sequence was defined at the silence over 3 seconds. Total of 1174 audible calls were detected from total of 12 hours data set (from 3:50 to 6:50 01-04 March 2004). Chirp were observed more than trill calls (567 chirps and 67 trills). Chirp-tochirp transitions were most frequency observed (81.68%), whereas trill-to-trill transitions were the least (4.27%). Transitions between the two types of calls were also observed (6.98%, 7.07%). Trill appeared in the middle and the end of a call sequence. The position of the trill did not differ between wild individual in Thailand and a captive individual from off Philippine that are considered to be separated populations. The stability of the sequence of each type of calls in a call sequence is investigated. Unlike song of birds or baleen whales, the call sequence pattern of dugong suggests small difference across the populations. The call sequence analysis as well as the behavioral context observation will provide the key to interpret function of dugong calls. ©2006 IEEE.

Underwater ultrasonic sound of finless porpoises Neophocaena phocaenoides were monitored concurrent with visual observations in the Yangtze River, China. In a total of 774 km cruise, 588 finless porpoises were sighted by visual observation and 44,864 ultrasonic pulses were recorded. The acoustic monitoring system could detect presence of the finless porpoises 82% of the time. False alarm in the system occurred with a frequency of 0.9%. The high frequency acoustical observation is suggested as an effective method for field surveys of small cetaceans, which produce high frequency sonar signals.

For quantitative assessments of the effect of artificial reefs to accumulate fish school. we developed a low cost fish school monitoring system (FISCHOM). which enables visual and acoustical observation of fish resources for more than several days. In this paper, we report the profile of prototype FISCHOM and the outcome of trial survey. FISHCOM is consisted of two sensors (a stereo camera with two strobe lights and an echo sounder), a programmable timer, a battery, and a pressure resistant housing with a visually and acoustically transparent window for the sensors. All components except for the housing were selected from inexpensive articles on the market. A digital camera captured two visual images apart 50 cm away each other, which was combined together by a stereo photogrammetric mirror. The stereo images enable us to measure the three-dimensional information of fish school (e.g. fish length tilt angle, distribution). Two sensors acquire a set of data every optional interval (from several seconds to hours) controlled by the programmable timer. A trial survey was carried out at a high-rise artificial reef located off Atsumi, Yamagata prefecture on May 2003. FISCHOM succeeded a 5 days monitoring with an hour interval of data acquisition. We obtained a time series data of individual number of fish, fish length and distance from FISHCOM by the stereo camera, and fish school distribution by the echo sounder. We have demonstrated that the FISCHOM is appropriate to obtain quantitative and continuous data of fish school than other observation methods, which commonly used for the artificial reef assessment, such as observation by SCUBA diver, angling sampling and fish echo sounder operated on a boat.

Dugongs (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.
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 Infrastructure
December 13-14, 2005, Siam City Hotel, Bangkok, Thailand

Cetacean's sonar is an appropriate model of underwater acoustical sensing technology. Sonar behavior of three free-ranging finless porpoises in an oxbow of the Yangtze River was observed by micro data logger systems attached on the animals. Newly developed acoustic data logger could record porpoise's sonar pulse events 1000 times every second with the amplitude information. Close correlation between sonar effort and behavioral context could be observed. Frequent use of sonar with various inter-pulse intervals was recorded during quick body movements characterized by spiky change of heaving acceleration. The inter-pulse intervals were precisely controlled to adjust the distance to a remote target, which was similar to the terminal phase in bat's sonar behavior. © 2004 IEEE.

Chinese River Dolphin (Lipotes vexillifer), usually called 'baiji', is one of the most endangered mammals in the world. The preservation of these mammals directly ensures the health of the ecosystem. However, not much behavioral information on baiji is available so far, that could effectively assist in undertaking their preservation. This research is an attempt to reveal baiji's hitherto unknown underwater dynamic behavior. For this work we have analyzed and extracted motion parameters from clicks of a free-swimming baiji recorded in 1996 at a single hydrophone. The absence of detailed bottom information made it difficult to localize baiji using the multiple reflections and forced us to rely completely on surface reflections only. From measurements of time delay between the direct path and the surface echo, not only large-scale behavior but also fine-scale behavior has been revealed, such as: periods of diving and surfacing, circling behavior underwater and a characteristic nodding motion. These studies have contributed towards a broad understanding of baiji's foraging exercises from the standpoint of formulating an acoustical survey for the search for this endangered marine mammal.

Dolphins have highly developed sonar abilities and have been studied extensively in captivity. The use of sonar by dolphins and porpoises in the wild is thought to be related to the underwater navigation and searching behavior. Here we report a new and simple method to archive continuous click events individually. Echolocation click events and swimming speed of finless porpoises (Neophocaena phocaenoides) were recorded with data loggers attached on the animals. The echolocation range converted from sonar pulse intervals in open waters ranged up to 130 m. Echolocation of free-ranging dolphins appears to adapt to various distance in navigation or ranging. Silent swim distance, calculated by the swim speed multiplied by the duration of the non-echolocating periods, was smaller than the echolocation range. Finless porpoises are believed to examine their frontal area acoustically using echolocation. In other words, the observed finless porpoises swam without echolocation only in an already inspected area.

Dolphins have bio-sonar ability called echoiocation. Clicks, echolocation signals, provide various biological information, such as, species, target range and acoustical survey effort of dolphins. Acoustical measurement is anewly developed method to observe underwater behavior of vocalizing animals.