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Phocoenids are generally considered to be nonwhistling species that produce only high-frequency pulsed sounds. Here our results show that neonatal finless porpoises (Neophocaena phocaenoides) frequently produce clear low-frequency (2-3 kHz) pulsed signals, without distinct high-frequency energy, just after birth and can produce both low- (2-3 kHz) and high-frequency (>100 kHz) pulsed signals simultaneously until about 20 days postnatal. The results indicate that low-frequency signals of neonatal finless porpoises are not an early form of high-frequency signals and suggest that low- and high-frequency signals may be produced by different sound production mechanisms. (C) 2008 Acoustical Society of America.

(2008). INDIRECT EVIDENCE OF BOAT AVOIDANCE BEHAVIOR OF YANGTZE FINLESS PORPOISES. Bioacoustics: Vol. 17, No. 1-3, pp. 174-176.

SUMMARY The hearing and echolocation clicks of a stranded Indo-Pacific humpback dolphin (Sousa chinensis) in Zhuhai, China, were studied. This animal had been repeatedly observed in the wild before it was stranded and its age was estimated to be ~40 years. The animal's hearing was measured using a non-invasive auditory evoked potential (AEP) method. Echolocation clicks produced by the dolphin were recorded when the animal was freely swimming in a 7.5 m (width)×22 m (length)×4.8 m (structural depth) pool with a water depth of ~2.5 m. The hearing and echolocation clicks of the studied dolphin were compared with those of a conspecific younger individual, ~13 years of age. The results suggested that the cut-off frequency of the high-frequency hearing of the studied dolphin was ~30–40 kHz lower than that of the younger individual. The peak and centre frequencies of the clicks produced by the older dolphin were ~16 kHz lower than those of the clicks produced by the younger animal. Considering that the older dolphin was ~40 years old, its lower high-frequency hearing range with lower click peak and centre frequencies could probably be explained by age-related hearing loss (presbycusis).

The biosonar (click train) production rate of ten Yangtze finless porpoises and their behavior were examined using animal-borne data loggers. The sound production rate varied from 0 to 290 click trains per 10-min time interval. Large individual differences were observed, regardless of body size. Taken together, however, sound production did not differ significantly between daytime and nighttime. Over the 172.5 h of analyzed recordings, an average of 99.0% of the click trains were produced within intervals of less than 60 s, indicating that during a 1-min interval, the number of click trains produced by each porpoise was typically greater than one. Most of the porpoises exhibited differences in average swimming speed and depth between day and night. Swimming speed reductions and usage of short-range sonar, which relates to prey-capture attempts, were observed more often during nighttime. However, biosonar appears to be affected not only by porpoise foraging, but also by their sensory environment, i.e., the turbid Yangtze River system. These features will be useful for passive acoustic detection of the porpoises. Calculations of porpoise density or abundance should be conducted carefully because large individual differences in the sound production rate will lead to large estimation error.

Broadband recording systems were adapted to characterize the whistle characteristics of free-ranging Indo-Pacific humpback dolphins (Sousa chinensis) in Sanniang Bay, China. A total of 4630 whistles were recorded, of which 2651 with legible contours and relatively good signal-to-noise ratios were selected for statistical analysis. Of the six tonal types (i.e., flat, down, rise, convex, U-shaped, and sine), flat (N - 1426; 39.45%) was the most predominant, followed by down (N - 754; 23.35%) and rise (N - 489; 12.34%). The whistles showed a short duration (mean +/- SD: 370.19 +/- 285.61 ms; range: 29-2923 ms), a broad frequency range (fundamental contour ranged from 0.52 to 33 kHz), and two harmonics (mean +/- SD: 1.90 +/- 2.74, with the maximum frequency of harmonics beyond 96 kHz). Whistles without gaps and stairs accounted for 76.7% and 86.4%, respectively. No significant interspecies differences in frequency parameters were observed compared with S. teuszii, which is inconsistent with morphological taxonomies but confirms phylogenetic results, thus suggesting a close relation between Chinese S. chinensis and Atlantic S. teuszii. Significant intra- and interspecific differences in the genus Sousa were also observed, indicating that animal vocalization may not be limited by genetically determined traits but could also be a function of local habitat adaptation. (C) 2013 Acoustical Society of America.

SummaryHow an animal receives sound may influence its use of sound. While "jaw hearing" is well supported for odontocetes, examining how sound is received across the head work has been limited to a few representative species. The substantial variation in jaw and head morphology among odontocetes suggests variation in sound reception. Here we address how a divergent subspecies, the Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) hears low, mid, and high frequency tones, as well as broadband clicks, comparing sounds presented at different locations across the head. Hearing was measured using auditory evoked potentials (AEPs). Click and tone stimuli (8, 54, and 120 kHz) were presented at nine locations on the head and body using a suction-cup transducer. Threshold differences were compared between frequencies and locations, and referenced to the underlying anatomy using computed tomography (CT) imaging of deceased animals of the same subspecies. The best hearing locations with minimum thresholds were found adjacent to a mandibular fat pad and overlying the auditory bulla. Mean thresholds were not substantially different at locations from the rostrum tip to the ear (11.6 dB). This contrasts with tests with bottlenose dolphins and beluga whales, in which 30-40 dB threshold differences were found across the animals' heads. Response latencies increased with decreasing response amplitudes, which suggests that both latency and sensitivity are interrelated when considering sound reception across the odontocete head. The results suggest that there are differences among odontocetes in the anatomy related to receiving sound, and porpoises may have relatively less acoustic "shadowing".

Summary An evoked-potential audiogram was measured for an Indo-Pacific humpback dolphin (Sousa chinensis) living in the Dolphinarium of Nanning Zoo, China. Rhythmic 20 ms pip trains composed of cosine-enveloped 0.25 ms tone pips at a pip rate of 1 kHz were presented as sound stimuli. The dolphin was trained to remain still at the water surface and to wear soft latex suction-cup electroencephalography (EEG) electrodes used to measure the animal's envelope-following evoked potentials to the sound stimuli. Responses to 1000 rhythmic 20 ms pip trains for each amplitude/frequency combination were averaged and analysed using a fast Fourier transform to obtain an evoked auditory response. The hearing threshold was defined as the zero crossing point of the response input-output function using linear regression. Fourteen frequencies ranging from 5.6 to 152 kHz were studied. The results showed that most of the thresholds were lower than 90 dB re. 1μPa (root mean square, r.m.s.), covering frequency range from 11.2 to 128 kHz, and the lowest threshold of 47 dB was measured at 45 kHz. The audiogram, which is a function of hearing threshold-versus-stimulus carrier frequency, presented a 'U'-shape with a region of high hearing sensitivity (within 20 dB of the lowest threshold) between approximately 20 and 120 kHz. At frequencies lower than this high-sensitivity region, thresholds increased at a rate of approximately 11 dB/octave, up to 93 dB at 5.6 kHz. The thresholds at high frequencies above 108 kHz increased steeply with a rate of 130 dB/octave, up to 127 dB at 152 kHz.

In Yangtze finless porpoises Neophocaena phocaenoides asiaeorientalis, the effects of fatiguing noise on hearing thresholds at frequencies of 32, 45, 64, and 128 kHz were investigated. The noise parameters were: 0.5-oct bandwidth, -1 to +0.5 oct relative to the test frequency, 150 dB re 1 mu Pa (140-160 dB re 1 mu Pa in one measurement series), with 1-30 min exposure time. Thresholds were evaluated using the evoked-potential technique allowing the tracing of threshold variations with a temporal resolution better than 1 min. The most effective fatiguing noise was centered at 0.5 octave below the test frequency. The temporary threshold shift (TTS) depended on the frequencies of the fatiguing noise and test signal: The lower the frequencies, the bigger the noise effect. The time-to-level trade of the noise effect was incomplete: the change of noise level by 20 dB resulted in a change of TTS level by nearly 20 dB, whereas the tenfold change of noise duration resulted in a TTS increase by 3.8-5.8 dB. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3596470]

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.

Detecting objects in their paths is a fundamental perceptional function of moving organisms. Potential risks and rewards, such as prey, predators, conspecifics or non-biological obstacles, must be detected so that an animal can modify its behavior accordingly. However, to date few studies have considered how animals in the wild focus their attention. Dolphins and porpoises are known to actively use sonar or echolocation. A newly developed miniature data logger attached to a porpoise allows for individual recording of acoustical search efforts and inspection distance based on echolocation. In this study, we analyzed the biosonar behavior of eight free-ranging finless porpoises and demonstrated that these animals inspect the area ahead of them before swimming silently into it as depicted in the figure. Before to get out of the inspected area, the porpoise use sonar. The porpoises inspected distances up to 77 m, whereas their swimming distance without using sonar was less than 20 m. The inspection distance was long enough to ensure a wide safety margin before facing real risks or rewards. Once a potential prey item was detected, porpoises adjusted their inspection distance from the remote target throughout their approach. Application of biosonar for biomimetic sonar is discussed.

Background: Observing and monitoring the underwater social interactions of cetaceans is challenging. Therefore, previous cetacean studies have monitored these interactions by surface observations. However, because cetaceans spend most of their time underwater, it is important that their underwater behavior is also continuously monitored to better understand their social relationships and social structure. The finless porpoise is small and has no dorsal fin. It is difficult to observe this species in the wild, and little is known of its sociality. Methodology/Principal Findings: The swim depths of 6 free-ranging finless porpoises were simultaneously recorded using a time-synchronized bio-logging system. Synchronous diving was used as an index of association. Two pairs, # 27 (an immature female estimated to be 3.5 years old) and # 32 (an adult male), # 28 (a juvenile male estimated to be 2 years old) and # 29 (an adult male), tended to participate in long periods of synchronized diving more frequently than 13 other possible pairs, indicating that the 4 porpoises chose their social partners. The adult males (# 32, # 29) tended to follow the immature female (# 27) and juvenile male (# 28), respectively. However, during synchronized diving, the role of an initiator often changed within the pair, and their body movements appeared to be non-agonistic, e. g., rubbing of bodies against one another instead of that on one-side, as observed with chasing and escaping behaviors. Conclusions/Significance: The present study employed a time-synchronized bio-logging method to observe the social relationships of free-ranging aquatic animals based on swimming depth. The results suggest that certain individuals form associations even if they are not a mother and calf pair. Long synchronized dives occurred when particular members were reunited, and this suggests that the synchronized dives were not a by-product of opportunistic aggregation.

A method is presented to estimate the density of finless porpoises using stationed passive acoustic monitoring. The number of click trains detected by stereo acoustic data loggers (A-tag) was converted to an estimate of the density of porpoises. First, an automated off-line filter was developed to detect a click train among noise, and the detection and false-alarm rates were calculated. Second, a density estimation model was proposed. The cue-production rate was measured by biologging experiments. The probability of detecting a cue and the area size were calculated from the source level, beam patterns, and a sound-propagation model. The effect of group size on the cue-detection rate was examined. Third, the proposed model was applied to estimate the density of finless porpoises at four locations from the Yangtze River to the inside of Poyang Lake. The estimated mean density of porpoises in a day decreased from the main stream to the lake. Long-term monitoring during 466 days from June 2007 to May 2009 showed variation in the density 0-4.79. However, the density was fewer than 1 porpoise/km(2) during 94% of the period. These results suggest a potential gap and seasonal migration of the population in the bottleneck of Poyang Lake. (c) 2010 Acoustical Society of America. [DOI: 10.1121/1.3442574]

We focally observed the suckling behavior of two Yangtze finless porpoise calves, C05 and C07, in captivity. Between 15 and 730 days postpartum of C05 and between birth and 30 days postpartum of C07, 286.3 (1.9 ± 0.4 hr/day (mean ± standard deviation), n = 148 days) and 18.3 hr (2.0 ± 0.5 hr/day, n = 9 days) of video footage were recorded, in which 429 and 111 suckling events were observed, respectively. We found that the calves made their initial suckling attempts after repeated stroking of the mother's body with their rostrums. The suckling duration was 4.4 ± 1.8 sec and 4.8 ± 2.4 sec, respectively. Before suckling, the calves swam under the mother's genital region (99.1% of number of event, respectively). During suckling, the mother generally turned sideways to facilitate the calves' suckling (80.7 and 76.6%, respectively). The calves almost equally used the two mammary slits [52.2% (left) and 47.8% (right), and 44.1% (left) and 55.9% (right), respectively]. The frequency and proportion of time C05 spent suckling continuously decreased to zero by 483 days postpartum. The two variables for C07 increased following birth, to a peak at 16 days postpartum, and then decreased continuously until 30 days postpartum. We discuss the possible implications of these observations for the management and conservation of this endangered cetacean.

The detection performance regarding stationary acoustic monitoring of Yangtze finless porpoises Neophocaena phocaenoides asiaeorientalis was compared to visual observations. Three stereo acoustic data loggers (A-tag) were placed at different locations near the confluence of Poyang Lake and the Yangtze River, China. The presence and number of porpoises were determined acoustically and visually during each 1-min time bin. On average, porpoises were acoustically detected 81.7 +/- 9.7% of the entire effective observation time, while the presence of animals was confirmed visually 12.7 +/- 11.0% of the entire time. Acoustic monitoring indicated areas of high and low porpoise densities that were consistent with visual observations. The direction of porpoise movement was monitored using stereo beams, which agreed with visual observations at all monitoring locations. Acoustic and visual methods could determine group sizes up to five and ten individuals, respectively. While the acoustic monitoring method had the advantage of high detection probability, it tended to underestimate group size due to the limited resolution of sound source bearing angles. The stationary acoustic monitoring method proved to be a practical and useful alternative to visual observations, especially in areas of low porpoise density for long-term monitoring.

Yangtze finless porpoises were surveyed by using simultaneous visual and acoustical methods from 6 November to 13 December 2006. Two research vessels towed stereo acoustic data loggers, which were used to store the intensity and sound source direction of the high frequency sonar signals produced by finless porpoises at detection ranges up to 300 m on each side of the vessel. Simple stereo beam forming allowed the separation of distinct biosonar sound source, which enabled us to count the number of vocalizing porpoises. Acoustically, 204 porpoises were detected from one vessel and 199 from the other vessel in the same section of the Yangtze River. Visually, 163 and 162 porpoises were detected from two vessels within 300 m of the vessel track. The calculated detection probability using acoustic method was approximately twice that for visual detection for each vessel. The difference in detection probabilities between the two methods was caused by the large number of single individuals that were missed by visual observers. However, the sizes of large groups were underestimated by using the acoustic methods. Acoustic and visual observations complemented each other in the accurate detection of porpoises. The use of simple, relatively inexpensive acoustic monitoring systems should enhance population surveys of free-ranging, echolocating odontocetes.

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 ).

A growing demand for sustainable energy has led to an increase in construction of offshore windfarms. Guishan windmill farm will be constructed in the Pearl River Estuary, China, which sustains the world’s largest known population of Indo-Pacific humpback dolphins (Sousa chinensis). Dolphin conservation is an urgent issue in this region. By using passive acoustic monitoring, a baseline distribution of data on this species in the Pearl River Estuary during pre-construction period had been collected. Dolphin biosonar detection and its diel, lunar, seasonal and tidal patterns were examined using a Generalized Linear Model. Significant higher echolocation detections at night than during the day, in winter-spring than in summer-autumn, at high tide than at flood tide were recognized. Significant higher echolocation detections during the new moon were recognized at night time. The diel, lunar and seasonal patterns for the echolocation encounter duration also significantly varied. These patterns could be due to the spatial-temporal variability of dolphin prey and illumination conditions. The baseline information will be useful for driving further effective action on the conservation of this species and in facilitating later assessments of the effects of the offshore windfarm on the dolphins by comparing the baseline to post construction and post mitigation efforts.

The clicks of Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis) from 7 individuals in the tank of Baiji aquarium, 2 individuals in a netted pen at Shishou Tian-e-zhou Reserve and 4 free-ranging individuals at Tianxingzhou were recorded using a broadband digital recording system with four element hydrophones. The peak-to-peak apparent source level (ASL_pp) of clicks from individuals at the Baiji aquarium was 167 dB re 1 μPa with mean center frequency of 133 kHz, -3dB bandwidth of 18 kHz and -10 dB duration of 58 μs. The ASL_pp of clicks from individuals at the Shishou Tian-e-zhou Reserve was 180 dB re 1 μPa with mean center frequency of 128 kHz, -3dB bandwidth of 20 kHz and -10 dB duration of 39 μs. The ASL_pp of clicks from individuals at Tianxingzhou was 176 dB re 1 μPa with mean center frequency of 129 kHz, -3dB bandwidth of 15 kHz and -10 dB duration of 48 μs. Differences between the source parameters of clicks among the three groups of finless porpoises suggest these animals adapt to their echolocation signals depending on their surroundings.

The reconstruction of the acoustic properties of a neonate finless porpoise's head was performed using X-ray computed tomography (CT). The head of the deceased neonate porpoise was also segmented across the body axis and cut into slices. The averaged sound velocity and density were measured, and the Hounsfield units (HU) of the corresponding slices were obtained from computed tomography scanning. A regression analysis was employed to show the linear relationships between the Hounsfield unit and both sound velocity and density of samples. Furthermore, the CT imaging data were used to compare the HU value, sound velocity, density and acoustic characteristic impedance of the main tissues in the porpoise's head. The results showed that the linear relationships between HU and both sound velocity and density were qualitatively consistent with previous studies on Indo-pacific humpback dolphins and Cuvier's beaked whales. However, there was no significant increase of the sound velocity and acoustic impedance from the inner core to the outer layer in this neonate finless porpoise's melon.

Source levels of echolocating free-ranging Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) were calculated using a range estimated by measuring the time delays of the signals via the surface and bottom reflection paths to the hydrophone, relative to the direct signal. Peak-to-peak source levels for finless porpoise were from 163.7 to 185.6 dB re:1 mu Pa. The source levels are highly range dependent and varied approximately as a function of the one-way transmission loss for signals traveling from the animals to the hydrophone. (c) 2006 Acoustical Society of America.

Chinese Acad Sci, Inst Hydrobiol, Wuhan 430072, Peoples R China; Texas AM Downstream Res Grp, Amelia Isl, FL 32034 USA; Conservat Int, Washington, DC 20036 USA

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.

As the sole freshwater subspecies of finless porpoise (Neophocaena phocaenoides), the Yangtze finless porpoise (N. p. asiaeorientalis) lives only in the middle and lower reaches of the Yangtze River and its appended Poyang and Dongting Lakes. As a result of human activity on the river, including over and illegal fishing, pollution, transportation and dam construction, the population of Yangtze finless porpoises has been steadily and rapidly decreasing during the past several decades, which leads the animal to be endangered.For saving this unique animal from extinction, three corresponding measures, in situ conservation, ex situ conservation, and intensifying breeding research in captivity, were proposed and have been implemented since the 1980s.After successfully rearing the animals in captivity for almost nine years, the first Yangtze finless porpoise was successfully born in captivity on July 5, 2005. The calf is male, with a body length of 69 cm. This is the first freshwater cetacean ever born in captivity.The successful birth of this calf confirms that it is possible to breed the Yangtze finless porpoise in captivity. Furthermore, this will greatly benefit the conservation efforts, and also greatly bolster our on-going efforts to study the reproductive biology of these animals.More studies and efforts are expected to establish a sustainable, captive colony of the Yangtze finless porpoise, which will not only greatly expand our knowledge about the reproduction biology of this animal, but also help to redeem the wild population through a careful yearly 'soft releasing' process.

This paper describes the high-frequency echolocation signals from free-ranging Yangtze finless porpoise in the Tian-e-zhou Baiji National Natural Reserve in Hubei Province, China. Signal analysis showed that the Yangtze finless porpoise clicks are typical high-frequency narrow-band (relative width of the frequency spectrum Q = 6.6 +/- 1.56, N = 548) ultrasonic pulses. The peak frequencies of the typical clicks range from 87 to 145 kHz with an average of 125 +/- 6.92 kHz. The durations range from 30 to 122 micros with an average of 68 +/- 14.12, as. The characteristics of the signals are similar to those of other members of the Phocoenidae as well as the distantly related delphinids, Cephalorhynchus spp. Comparison of these signals to those of the baiji (Lipotes vexillifer), who occupies habitat similar to that of the Yangtze finless porpoise, showed that the peak frequencies of clicks produced by the Yangtze finless porpoise are remarkably higher than those produced by the baiji. Difference in peak frequency between the two species is probably linked to the different size of preferred prey fish. Clear double-pulse and multi-pulse reverberation structures of clicks are noticed, and there is no indication of any low-frequency (< 70 kHz) components during the recording period.

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 microdata 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

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.

Anthropogenic noise in aquatic environments is a worldwide concern due to its potential adverse effects on the environment and aquatic life. The Hongkong-Zhuhai-Macao Bridge is currently under construction in the Pearl River Estuary, a hot spot for the Indo-Pacific humpbacked dolphin (Sousa chinensis) in China. The OCTA-KONG, the world's largest vibration hammer, is being used during this construction project to drive or extract steel shell piles 22 m in diameter. This activity poses a substantial threat to marine mammals, and an environmental assessment is critically needed. The underwater acoustic properties of the OCTA-KONG were analyzed, and the potential impacts of the underwater acoustic energy on Sousa, including auditory masking and physiological impacts, were assessed. The fundamental frequency of the OCTA-KONG vibration ranged from 15 Hz to 16 Hz, and the noise increments were below 20 kHz, with a dominant frequency and energy below 10 kHz. The resulting sounds are most likely detectable by Sousa over distances of up to 3.5 km from the source. Although Sousa clicks do not appear to be adversely affected, Sousa whistles are susceptible to auditory masking, which may negatively impact this species' social life. Therefore, a safety zone with a radius of 500 m is proposed. Although the zero-to-peak source level (SL) of the OCTA-KONG was lower than the physiological damage level, the maximum root-mean-square SL exceeded the cetacean safety exposure level on several occasions. Moreover, the majority of the unweighted cumulative source sound exposure levels (SSELs) and the cetacean auditory weighted cumulative SSELs exceeded the acoustic threshold levels for the onset of temporary threshold shift, a type of potentially recoverable auditory damage resulting from prolonged sound exposure. These findings may aid in the identification and design of appropriate mitigation methods, such as the use of air bubble curtains, "soft start" and "power down" techniques.

Information on the habitat use of the critically endangered Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is critical for its conservation. The diel biosonar behavior of the porpoise in the port areas of the Yangtze River was examined along with simultaneous observations of fish density and boat traffic. Biosonar pulses from the porpoises were detected for 1233 min (5.77%) over a 21,380 min duration of effective observations. In total, 190 (5.63%) buzzes (an indication of prey capture attempts) were recorded among the 3372 identified click trains. Of the 168 echolocation encounters (bouts of click trains less than eight min apart), 150 (89.3%) involved single animals, indicating that solitary porpoises were frequently present and feeding in the port areas. Significant diel patterns were evident involving the biosonar behavior of the porpoises (including click trains and buzzes), fish density and boat traffic. The frequencies of the click trains and buzzes were significantly lower during the day than in the evening and at night, which suggests that porpoises in this region are primarily engaged in crepuscular and nocturnal foraging. The lack of a significant diel pattern in the echolocation encounters indicates the importance of the port in porpoise conservation. A forced feeding schedule may be associated with the lack of a significant correlation between porpoise acoustics and boat traffic. Overall, prey availability appears to be the primary factor that attracts porpoises. Additionally, porpoises tend to migrate or remain downstream in the morning and migrate or remain upstream in the evening, most likely to follow their prey. The findings of this study can be used to improve the conservation of the Yangtze finless porpoise.

Echolocation click events of a free-ranging juvenile and an adult finless porpoise (Neophocaena phocaenoides) were recorded with an acoustic data logger. Additionally, dive depth and swim speed of the juvenile were recorded with a behavior data logger. Echoes of echolocation signals from the water surface were clearly detected in shallow dives approximately less than 2 m. The delay time between a surface echo and a direct signal corresponded with the two-way transmission time for the animal’s depth, indicating that the signals originated from the animal wearing the data loggers. The finless porpoises produced echolocation signals frequently and were thought to be able to detect their depth by listening to echoes from the water surface.

Observing and monitoring underwater social interactions of cetaceans is challenging. Because cetaceans spend most of their time underwater, it is important to monitor their underwater behavior individually. The finless porpoise is small and has no available natural identification marks that causes little knowledge of its sociality. Here we used acoustic datalogger to synchronize individual depth profile among individuals within a second. Acoustic and behavior tags were deployed on six free-ranging finless porpoises simultaneously and released in open water. Echolocation sounds were used as the trigger signal to synchronize the clock of all logging systems. Synchronous dives characterized by similar time-depth profile were used as an index of association. Two pairs tended to participate in long periods of synchronized diving more frequently than 13 other possible pairs, indicating that these four porpoises chose their social partners. Initiator and follower could be identified by precisely time synchronize...

In recent 10 years, a miniature stereo acoustic data logger (A-tag, W20-AS, Little Leonardo, Japan) has been used to observe the bio-sonar behaviour of free-ranging Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis). The A-tag is small enough to be attached on the one of the smallest odontocetes by using suction cups. The A-tag with two external hydrophones can record the sonar pulse intensity, inter-click-intervals, and sound source direction measured by time arrival difference of sounds at the two hydrophones. Major outcomes by A-tag were the in situ off-axis sonar beam pattern, attention and approach phase of biosonar behaviour, scanning sonar of rolling animals, and social contacts among free-ranging Yangtze finless porpoises. In addition, frequent ultrasonic sound production was confirmed that seemed to be a reason of high detection performance of this species using passive acoustic monitoring of finless porpoises. This biosonar monitoring method using miniature data logger system de...

Two large freshwater lakes in China (Poyang and Dongting Lakes) are crucial habitats of the Yangtze finless porpoises. The lakes are confronted with threatens from low water levels. For evaluating possible impacts of low water levels on the porpoises in the lakes, the distribution patterns of the animals in the lakes were monitored in different seasons by using a boat-towing A-tag array from 2009 through 2011. The survey routes were almost same among different seasons. The acoustical detection number (i.e. encounter number) of porpoise in every 3-km section was calculated by counting the bearing angle traces of the sonar sources recorded by the array. The numbers in the same section were compared between high and low water level periods. Results indicated that porpoises appeared to congregate in deep water areas in low water level periods, while they tended to disperse toward the near shore waters in high water level periods. The results suggest concentration of individuals during low water level period. The variations of distribution patterns in different water level periods remind us that protection efforts should be focused on different areas according to the changes of water levels in different seasons.

Passive acoustic monitoring has been widely applied to observe the presence, movement and behavior of the target species. For quantitative analysis, the acoustic cue production rate of the target animals must be observed in advance. We examined the detailed pattern of biosonar and swimming behaviors of 10 Yangtze finless porpoises (1 female and 9 males) obtained by electronic tags attached to the animals. The click trains produced by the tagged animal were identified out of other animals' vocalizations using bearing angles calculated by the time-of- arrival differences of the sounds between the two hydrophones in the acoustic tag. The number of click trains produced in 10 min did not relate to the body size or sex and varied from 0 to 290. Although deeper the animals dive, faster they swam, the speed or maximum depth of the animals had no correlation with the number of click trains produced or body size. All parameters we examined had no diurnal rhythm but had independent aperiodic variation. The sound production rate without day or night bias is suitable for the quantitative passive acoustic monitoring of this species.

A stereo passive acoustic event recorder (A-tag) has been applied for range-wide monitoring of baiji and finless porpoises in China. As the pilot study, two research vessels were operated in 1700 km historic habitat of both species from Yichang to Shanghai in 2006. There was no detection of baiji, but 204 and 199 porpoises were counted acoustically by two vessels, respectively. In order to investigate the population trends of cetaceans, periodical survey is necessary. We installed A-tag on the cargo ship, which was operated 1100 km in the river once every month. An average of 6059 clicks and 95 porpoises were acoustically detected in each survey. Detected group sizes of the animals in 120-s time window were not significantly different among the surveys, but the distribution pattern suggested seasonal migration. The animals were detected in most of the survey range except two gap sections with 40 and 60 km lengths, down from Wuhan and Nanjing cities, respectively, where no animals were detected in the first three surveys. Fragmentation of population by anthropological factors was concerned. The cargo ship based passive acoustic survey was effective to monitor the distribution and population trend over time.

The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is an endangered freshwater porpoise subspecies unique to the Yangtze River basin. Without immediate conservation measures, it could soon become extinct, just as the Yangtze River dolphin (baiji, Lipotes vexillifer). We report seasonal change in the local distribution of the porpoises living in the conjunction area of the middle reaches of the Yangtze River, side streams, and appended Poyang Lake. A towed stereo acoustic data-logger, A-tag, was used to detect echolocation signals and sound source bearing angles. The independent sound source directions provided the number of animals present, not just the number of sounds. Passive acoustic surveys were performed regularly from May 2007 to August 2010. The water level was highest in August (summer) and lowest in February (winter) and at mid-level in May (spring) and November (autumn). The average number of porpoises detected in 11 surveys conducted in different seasons varied from 0.5...

How an animal receives sound will influence how it uses or is impacted by sound. While the “jaw hearing” hypothesis is well supported, work has been limited to a few “representative” species. There are clear variations in the jaw and head morphologies of odontocete species suggesting subtle variation in sound reception. Here we address how a divergent cetacean species, the Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis), receives sound. Noise impacts on this subspecies are a concern as they inhabit waters with many acoustic sources. Hearing was measured using auditory evoked potentials. Click and amplitude modulated tone stimuli were presented at nine locations on the head and body using a jawphone transducer. Thresholds were compared to anatomical dissections and CT scans of porpoise heads. Minimum thresholds and best hearing locations were at the cheek‐fat‐pad and distal to the porpoise bulla. However, thresholds were not substantially different at locations from the rostrum tip to t...

Data on distribution, abundance, ecology, and behavior are essential for conservation and management of endangered animals in the wild. Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) is an endangered small odontocete species, living exclusively in the Yangtze River and its connecting Poyang and Dongting Lakes. Frequent production of high-frequency bio-sonar signals allows the animal to be detectable using passive acoustic methods. Recently, a stereo acoustic event data-logger (A-tag) has been used extensively to detect the animal by using both fixed and mobile platforms. The passive acoustic monitoring methods were not only successful in detecting the presence of animals, but also in counting, localizing, and tracking phonating individuals. Underwater behavior observed acoustically helped to assess possible effects of vessels on the animals during acoustic surveys.

The Chinese river dolphin or baiji (Lipotes vexillifer), which might be the most endangered cetacean in the world, lives only in the mainstream of the middle and lower reaches of the Yangtze river, China. Baiji is at the brink of extinction. There are approximately 200 individuals left in a 1600 km stretch of the river. The population size is decreasing mainly due to degradation of habitat, incidental capture by fisheries, and increased river traffic. Baiji lives in turbid water and some researchers have speculated that it may possess excellent echolocation and sound communication abilities. Morphometric studies, however, have suggested that the auditory and vestibular systems of baiji are relatively underdeveloped in comparison to those of some other dolphins, such as Tursiops Truncatus and Neophocaena phocaenoides (Feng et al., 1989). The objective of this paper is to estimate baiji’s hearing capability by determining its auditory thresholds using behavioral methods.

Counting the number of animals is essential for monitoring and management of marine mammals. Autonomous stereo acoustic event recorder (A‐tag) to identify each sound source enabled to count phonating odontocetes in the wild. Finless porpoises were surveyed by towed A‐tags in 1100 km stretch of Yangtze River from Wuhan to Shanghai. The calculated detection probability using acoustic method was approximately twice that for visual detection. The difference in detection probabilities between the two methods was caused by the large number of single individuals that were missed by visual observers. However, acoustics tended to underestimate group size due to the limited resolution of sound source bearing angles. The detection performance regarding stationary acoustic monitoring of this species was also examined. Three stereo acoustic data loggers were placed at different locations near the confluence of Poyang Lake and the Yangtze River. Acoustic monitoring confirmed the low density bottle neck of the population between the lake and the river that was consistent with visual observations. The passive pulse event monitoring was proved to be a practical and useful alternative to visual observations, especially for long‐term and range‐wide monitoring.

Finless porpoises (Neophocaena phocaenoides) are distributed in Asian waters. The narrow‐band and high‐frequency pulse sonar signals produced by this species are distinctive from background noises. Underwater sound monitoring by a hydrophone (BK8103) along board sides of a research vessel concurrent with visual observation were conducted in the Yangtze River from Wuhan to Poyang Lake in 1998. The peak‐to‐peak detection threshold level was 133 dB re: 1 μPa, which could be roughly converted to the theoretical detection range of 316 m, hypothesizing the porpoise directing to the hydrophone and 168‐dB source level of the sonar signal under a shallow water sound propagation (combination of spherical and cylindrical spreading). In a total of 1064‐km cruise, 717 finless porpoises were observed. The acoustical monitoring system could detect the sonar signals from finless porpoises, found within 200 m from the research vessel. The sonar signals could also be detected at night and under windy weather conditions. Basically, the acoustical observation system was operated automatically and free from the individual difference of observers. The high‐frequency acoustical monitoring seems to be an effective method for the survey of small cetaceans which produce sonar signals.

Acoustic signals from wild Neophocaena phocaenoides sunameri were recorded in the waters off Liao-dong-wan Bay located in Bohai Sea, China. Signal analysis shows that N. p. sunameri produced "typical" phocoenid clicks. The peak frequencies f(p), of clicks ranged from. 113 to 131 kHz with an average of 121 +/- 3.78 kHz (n=71). The 3 dB bandwidths Delta f ranged from 10.9 to 25.0 kHz with an average of 17.5 +/- 3.30 kHz. The signal durations At ranged from 56 to 109 mu s with an average 80 +/- 11.49 mu s. The number of cycles N, ranged from 7 to 13 with an average of 9 +/- 1.48. With increasing peak frequency there was a faint tendency of decrease in bandwidth, which implies a nonconstant value of f(p)/Delta f. On occasion there were some click trains with faint click energy presenting below 70 kHz, however, it was possibly introduced by interference effect from multiple pulses structures. The acoustic parameters of the clicks were compared between the investigated population and a riverine population of finless porpoise. (c) 2007 Acoustical Society of America.