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Wang Ding - One of the best experts on this subject based on the ideXlab platform.
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Common pattern of population decline for freshwater cetacean species in deteriorating habitats
2012Co-Authors: Huang Shiang-lin, Hao Yujiang, Wang Ding, Turvey, Samuel T., Mei Zhigang, Wang, Author), Chinese Acad Sci, Inst Hydrobiol, Key Lab Aquat Biodivers Conservat, Wuhan 430072, Hu China.Abstract:1. Freshwater cetacean species, including the baiji (Lipotes Vexillifer), Amazon River dolphin (Inia geoffrensis), Ganges/Indus River dolphins (Platanista spp.) and Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), apex predators in megariver ecosystems, face serious challenges owing to the deterioration of habitat quality. 2. We simulated population change of four freshwater cetacean species under increasing habitat deterioration. Carrying capacity (K) was used to represent the habitat quality, and a logistic model was used to describe the rate of habitat deterioration (dK). 3. An individual-based Leslie matrix model showed that population declines and extinctions in freshwater cetaceans under increasing habitat deterioration exhibit a consistent pattern irrespective of the initial level of K or population size. When dK is low, population abundance fluctuates stochastically around initial K, but a rapid increase in dK is accompanied by a sharp population decline, with a residual population ultimately declining continuously to extinction. 4. Simulations show that traditional census survey techniques used in cetacean species are unlikely to detect early signs of population decline before a critical level is reached. 5. Empirical data of the likely extinction of baiji strongly agree with our simulation exercise, implying that extinction of other freshwater cetacean species may occur sooner than previously considered. Hence, precautionary approaches for habitat restoration and landscape management should be implemented before freshwater cetacean population declines are detected, and ideally, before habitat quality begins to deteriorate.1. Freshwater cetacean species, including the baiji (Lipotes Vexillifer), Amazon River dolphin (Inia geoffrensis), Ganges/Indus River dolphins (Platanista spp.) and Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), apex predators in megariver ecosystems, face serious challenges owing to the deterioration of habitat quality. 2. We simulated population change of four freshwater cetacean species under increasing habitat deterioration. Carrying capacity (K) was used to represent the habitat quality, and a logistic model was used to describe the rate of habitat deterioration (dK). 3. An individual-based Leslie matrix model showed that population declines and extinctions in freshwater cetaceans under increasing habitat deterioration exhibit a consistent pattern irrespective of the initial level of K or population size. When dK is low, population abundance fluctuates stochastically around initial K, but a rapid increase in dK is accompanied by a sharp population decline, with a residual population ultimately declining continuously to extinction. 4. Simulations show that traditional census survey techniques used in cetacean species are unlikely to detect early signs of population decline before a critical level is reached. 5. Empirical data of the likely extinction of baiji strongly agree with our simulation exercise, implying that extinction of other freshwater cetacean species may occur sooner than previously considered. Hence, precautionary approaches for habitat restoration and landscape management should be implemented before freshwater cetacean population declines are detected, and ideally, before habitat quality begins to deteriorate
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Population status, threats and conservation of the Yangtze finless porpoise
Science Bulletin, 2009Co-Authors: Wang DingAbstract:The Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) is currently limited to the middle and lower reaches of the Yangtze River from Yichang to Shanghai, China, and the adjoining Poyang and Dongting Lakes. Its population size has decreased remarkably during the last several decades due to the heavy impact of human activities, including overfishing of prey species, water development projects that cause attendant habitat loss and degradation, water pollution, and accidental deaths caused by harmful fishing gear and collisions with motorized vessels. It was estimated that the number of remaining individuals was down to approximately 1800 in 2006, a number that is decreasing at a rate as high as 5% per year. Three conservation measures - in situ and ex situ conservation and captive breeding have been applied to the protection of this unique porpoise since the early 1990s. Seven natural and two “semi-natural” reserves have so far been established. Since 1996, a small group of finless porpoises has been successfully reared in a facility at the Institute of Hydrobiology of the Chinese Academy of Sciences; three babies were born in captivity on July 5, 2005, June 2, 2007 and July 5, 2008. These are the first freshwater cetaceans ever born in captivity in the world. Several groups of these porpoises caught in the main stream of the Yangtze River, or rescued, have been introduced into the Tian’e-Zhou Semi-natural Reserve since 1990. These efforts have proven that, not only can these animals survive in the area, they are also to reproduce naturally and successfully. More than 30 calves had been born in the reserve since then, with one to three born each year. Taking deaths and transfers into account, there were approximately 30 individuals living in the reserve as of the end of 2007. Among eight mature females captured in April 2008, five were confirmed pregnant. This effort represents the first successful attempt at off-site protection of a cetacean species in the world, and establishes a solid base for conservation of the Yangtze finless porpoise. A lesson must be drawn from the tragedy of Chinese River Dolphin (Lipotes Vexillifer), which has already been declared likely extinct. Strong, effective and appropriate protective measures must be carried out quickly to prevent the Yangtze finless porpoise from becoming a second Chinese River Dolphin, and save the biodiversity of the Yangtze River as a whole.
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Construction and characterization of a Lipotes Vexillifer genomic DNA BAC library
'Zoological Society of Japan', 2007Co-Authors: Zhang Xian-feng, Wang Ding, Fang Sheng-guo, Wang, D, Chinese Acad Sci, Inst Hydrobiol, Wuhan 430072, Peoples R ChinaAbstract:We constructed a genomic DNA library for Lipotes Vexillifer (L. Vexillifer), the Baiji or Yangtze River dolphin, one of the most endangered mammals in the world. The library consists of 149,000 BAC clones, with an average insert size of 83 kb, representing approximately 3.4 haploid genome equivalents. PCR amplification of four known L. Vexillifer genes yielded two to four positive clones each. To demonstrate the utility of this library, we isolated and sequenced the L. Vexillifer alpha lactalbumin gene, which is a gene specific to mammals and one which has been widely used as molecular tool in phylogenetic analysis. We also end-sequenced 20 randomly selected clones, resulting in the identification of at least five new L. vexilliter genes, five SSR loci, and one SINE locus. These results suggest that this library is a valuable resource for candidate gene cloning, physical mapping, and genome sequencing of this important and threatened species.We constructed a genomic DNA library for Lipotes Vexillifer (L. Vexillifer), the Baiji or Yangtze River dolphin, one of the most endangered mammals in the world. The library consists of 149,000 BAC clones, with an average insert size of 83 kb, representing approximately 3.4 haploid genome equivalents. PCR amplification of four known L. Vexillifer genes yielded two to four positive clones each. To demonstrate the utility of this library, we isolated and sequenced the L. Vexillifer alpha lactalbumin gene, which is a gene specific to mammals and one which has been widely used as molecular tool in phylogenetic analysis. We also end-sequenced 20 randomly selected clones, resulting in the identification of at least five new L. vexilliter genes, five SSR loci, and one SINE locus. These results suggest that this library is a valuable resource for candidate gene cloning, physical mapping, and genome sequencing of this important and threatened species
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review on breeding biology of yangtze finless porpoise neophocaena phocaenoides asiaeotientalis
Acta Theriologica Sinica, 2006Co-Authors: Hao Yujiang, Wang Ding, Zhang XianfengAbstract:There a re three Neophocaena phocaenoides subspecies recognized in Chinese waters: South China Sea population, N. p. pho caenoides; Yellow Sea population, N. p. sunameri; and Ya ngtze population, N. p. asiaeorientalis. The Yangtze pop ulation, or Yangtze finless porpoise, is the most endangered subspecies that onl y inhabits in the Yangtze River and its adjacent lake systems. It is a unique freshwater and relatively isolated population of the Neophocaena. The wild population of the Yangtze finless porpoise has decreased drastically in last two decades because it also ine scapably suffers the impacts of the deterioration of the Yangtze environm ent as the Baiji (Lipotes Vexillifer) does, such as constructio n of hydropower facilities, overmuch and illegal fishing, busy water traffic, an d heavily water pollution etc. It is no doubt that it is very important to prot ect and rehabilitate the natural Yangtze habitats. However, it seems that there is no chance for improvement of the Yangtze environment in the foreseeable future. Therefore, it is a practical measure to protect the animal from extinc tion by ex-situ conservation in a long run. Captive bree ding is seen as one of essential practices of the ex-situ conservation for this animal. Obviously, the necessary knowledge on breeding b iology plays a key role for successful captive breeding. To better understand t h e data on reproductive biology of the Yangtze finless porpoise, the previous wor ks on the reproduction of the animal in recent 30 years are reviewed. And the p r esent research status is expounded in terms of ecology, physiology, ethology, an atomy and histology. Some contradictions and controversial conclusions in previous studies are discussed in this paper. Furthermore, some important issu e s and urgent research points are also discussed to try to shed a light in furthe r studies on breeding biology, and it is also hoped to provide a base for breedi ng program of this animal in captivity.
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Range-wide Yangtze freshwater dolphin expedition: The last chance to see Baiji?
'Springer Science and Business Media LLC', 2006Co-Authors: Wang Kexiong, Zhang Xianfeng, Wang Ding, Pfluger August, Barrett Leigh, Wang, D, Chinese Acad Sci, Inst Hydrobiol, Wuhan 430072, Hubei, Peoples R ChinaAbstract:Background, Aim and Scope. There are two species of fresh water cetaceans surviving in the Yangtze River system in China: Baiji (Lipotes Vexillifer) and Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis). As a result of the expansion of human activities on the river, their distribution ranges appear to be decreasing and in the case of the Baiji, are even being restricted to several sections. The Baiji is the world's most critically endangered cetacean species with a population estimated at only a few tens of individuals. The Yangtze finless porpoise is the world's only freshwater-adapted population of the species, and it has been estimated that only around 1,000 individuals remain in the river system. In order to prevent the extinction of Baiji and a sharp decline in the abundance of the porpoise, in situ conservation (i.e. in the river) and two ex situ conservation (i.e. in semi-natural reserves and in captivity) strategies were proposed and have been implemented since the early 1990s. In view of both the severely endangered status of the animals and the severely degraded conditions of their habitats, the feasibility and actual status of these two strategies are raised for discussion. Main Features. The threats faced by the cetaceans are mainly from the unfettered exploitation of the river's resources. In the past 20 years, five nature reserves have been established along the river. Imposing maximum prohibition of harmful and illegal fishing methods in the reserves might prolong the process of extinction of these cetaceans in the wild, but so far, the administrative measures taken in the reserves have not yet kept the abundance from sharply declining. As human use of the river and its resources is expected to intensify for many decades into the future, the ability of the river to continue to support these species is certainly undecided. Therefore, rescuing animals from the river and establishing viable breeding populations in semi-natural reserves, in which the environment is similar to the main stream of the river, and in captivity, has to be considered urgently as the short-term goal of ex situ strategies. Since the abundance of porpoises is higher than that of the Baiji, we have first established breeding populations of them in the semi-natural reserves and in captivity. But, considering the extremely low density of Baiji in the river, an immediate range-wide Yangtze Baiji survey is an urgent need for locating and capturing sufficient Baiji for successfully establishing a breeding population of them in semi-natural reserves. Results. Two semi-natural reserves (in Shishou, Hubei Province, and Tongling, Anhui Province) have been set up along the river in order to establish breeding populations of the Baiji and the porpoises. So far, several small groups of porpoises that were caught in the main stream of the river have successively been introduced into the semi-natural reserves. Under careful management, these animals in both of the semi-natural reserves not only survive, but can also reproduce naturally and successfully. At least one or three calves were born in each reserve each year. Additionally, a breeding group of porpoises is being established at the Baiji Dolphinarium at the Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan. There are presently four adults and one calf living in the Dolphinarium. The calf, born in July, 2005, is the first captive bred Yangtze Finless Porpoise in the world. In preparation for the range-wide Yangtze cetacean survey, a 9-day pilot expedition on the river near Wuhan was conducted in March, 2006, in order to develop methods for locating the Baiji. No Baiji were expected to be seen in such a short period but about 40 porpoise sightings were observed. Results of the pilot survey indicated that traditional visual and acoustical survey methods for cetaceans should be adapted to find the elusive Baiji in the river. Currently, the range-wide Yangtze cetacean survey is in preparation. The survey will cover over 1,700 km of the Yangtze River from Yichang to Shanghai, and is expected to provide detailed information on Baiji and porpoise numbers and distribution patterns in the river. Discussion. Although the short-term goal of ex situ conservation is to rescue cetaceans from the river and to establish viable breeding populations in semi-natural reserves and in captivity, the long-term goal of releasing the animals back into the river when the threats have decreased and the natural environment has been improved, should not be neglected. Moreover, the in situ conservation efforts in the natural reserves, and even in the entire Yangtze River system, including the lakes, should not be ignored or abandoned at any time. The activities contributing to the conservation of the Baiji and the porpoise in the wild have the incidental effect of benefiting the entire Yangtze ecosystem and other rare threatened species. The dynamics of the groups of porpoises in semi-natural reserves should be monitored continually, in order to guide the establishment of breeding groups of Baiji in these semi-natural reserves in the near future. Conclusions. Under the existing severely degraded conditions of the Yangtze system, the sharply fall populations of Baiji and porpoises will not be suspended in the foreseeable future. Therefore, ex situ conservation should be emphasized, and the severely threatened Baiji in the river should be removed and translocated to semi-natural reserves for establishing viable breeding populations. The successful program of capturing, translocating and maintaining finless porpoises in the Shishou semi-natural reserve has demonstrated its adequacy as an ex situ environment for cetaceans. Following the successful pilot survey in the river, the immediate range-wide Yangtze cetacean survey is proposed and is in preparation. The range-wide survey is expected to ensure that any remaining Baiji can be found reliably and captured successfully after the survey. Recommendations and Perspectives. During the range-wide survey, not only the Baiji but also the porpoise as well as their habitats should be investigated based on visual and acoustical methods that adapted to the river and the animals. Meanwhile, the current risk levels to the Baiji and porpoises should be evaluated at each area where Baiji or porpoises can be reliably sighted. Any capture efforts should be targeted on the most threatened areas, or where there is maximum risk of injury or death. The immediate track of the Baiji should be carried out once a Baiji is sighted during the range-wide survey in order to obtain the movement route of the animals, which is crucial information for the successful capture operation. Additionally, the need to establish new semi-natural reserves for the porpoises should be placed on the agenda of local and central governments in the near future.Background, Aim and Scope. There are two species of fresh water cetaceans surviving in the Yangtze River system in China: Baiji (Lipotes Vexillifer) and Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis). As a result of the expansion of human activities on the river, their distribution ranges appear to be decreasing and in the case of the Baiji, are even being restricted to several sections. The Baiji is the world's most critically endangered cetacean species with a population estimated at only a few tens of individuals. The Yangtze finless porpoise is the world's only freshwater-adapted population of the species, and it has been estimated that only around 1,000 individuals remain in the river system. In order to prevent the extinction of Baiji and a sharp decline in the abundance of the porpoise, in situ conservation (i.e. in the river) and two ex situ conservation (i.e. in semi-natural reserves and in captivity) strategies were proposed and have been implemented since the early 1990s. In view of both the severely endangered status of the animals and the severely degraded conditions of their habitats, the feasibility and actual status of these two strategies are raised for discussion
Yu Zhang - One of the best experts on this subject based on the ideXlab platform.
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Inducing rostrum interfacial waves by fluid-solid coupling in a Chinese river dolphin (Lipotes Vexillifer )
Physical review. E, 2016Co-Authors: Zhongchang Song, Chong Wei, Yu Zhang, Xianyan WangAbstract:Through numerically solving the appropriate wave equations, propagation of biosonar signals in a Chinese river dolphin (baiji) was studied. The interfacial waves along the rostrum-tissue interfaces, including both compressional (longitudinal) and shear (transverse) waves in the solid rostrum through fluid-solid coupling were examined. The baiji's rostrum was found to effect acoustic beam formation not only as an interfacial wave generator but also as a sound reflector. The wave propagation patterns in the solid rostrum were found to significantly change the wave movement through the bone. Vibrations in the rostrum, expressed in solid displacement, initially increased but eventually decreased from posterior to anterior sides, indicating a complex physical process. Furthermore, the comparisons among seven cases, including the combination of (1) the rostrum, melon, and air sacs; (2) rostrum-air sacs; (3) rostrum-melon; (4) only rostrum; (5) air sacs-melon; (6) only air sacs; and (7) only melon revealed that the cases including the rostrum were better able to approach the complete system by inducing rostrum-tissue interfacial waves and reducing the differences in main beam angle and -3 dB beam width. The interfacial waves in the rostrum were considered complementary with reflection to determine the obbligato role of the rostrum in the baiji's biosonar emission. The far-field beams formed from complete fluid-solid models and non-fluid-solid models were compared to reveal the effects brought by the consideration of shear waves of the solid structures of the baiji. The results may provide useful information for further understanding the role of the rostrum in this odontocete species.
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The role of various structures in the head on the formation of the biosonar beam of the baiji (Lipotes Vexillifer)
The Journal of the Acoustical Society of America, 2016Co-Authors: Chong Wei, Zhongchang Song, Yu ZhangAbstract:The relative role of the various structures in the head of the baiji (Lipotes Vexillifer) is examined. A finite element approach was applied to numerically simulate the acoustic propagation through a dolphin's head to examine the relative role of the skull, air sacs, and melon in the formation of the biosonar beam in the vertical plane. The beam pattern obtained with the whole head in place is compared with the beam pattern when the air sac is removed and the other structures (skull and melon) are in place, with only the skull removed, and finally with only the melon removed. The beam pattern with the air sacs and skull intact and the melon removed closely resembled the beam pattern for the complete head, suggesting that the melon has a minor role in the formation of the beam. The beam pattern for the other two cases had very little resemblance to the beam pattern for the whole head. The air sacs seem to have a role of directing propagation of the signal toward the front and the skull prevents the sound propagating below the rostrum. The beam patterns along with a correlation analysis showed that the melon had only a slight influence on the shape and direction of the beam. The resultant beam exiting the head of the dolphin is the result of complex reflection processes within the head of the animal.
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Simulation of ultrasound beam formation of baiji (Lipotes Vexillifer) with a finite element model
The Journal of the Acoustical Society of America, 2014Co-Authors: Chong Wei, Yu ZhangAbstract:The baiji (Lipotes Vexillifer) of the Yangtze River possesses a sophisticated biosonar system. In this study, a finite element approach was used to numerically investigate the propagation of acoustic waves through the head of the Yangtze River dolphin, which possesses an inhomogeneous and complex structure. The acoustic intensity distribution predicted from models with and without the melon and/or skull showed that the emitted sound beam was narrow and formed a highly directed acoustic beam, and the skull and melon significantly enhanced the directional characteristics of the emitted sound. Finally, for a short duration impulsive source, the emitted sound pressure distributions were also simulated at different propagation times. The results provide useful information for better understanding the operation of the biosonar system in this rare and perhaps extinct animal.
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Enhance beam formation by airsacs and skull in Chinese river dolphin (Lipotes Vexillifer)
The Journal of the Acoustical Society of America, 2014Co-Authors: Chong Wei, Zhongchang Song, Yu ZhangAbstract:The melon of dolphins is considered by many as the structure responsible for the focusing of the biosonar beam. However, finite element numerical simulation of the head of the Chinese river dolphin (Lipotes Vexillifer) indicates that the biosonar beam is formed by reflections off the airsacs and bony structures in the skull. The finite element approach was applied to numerically simulate the acoustic propagation through dolphin's head in four several situations (complete head, skull only, skull plus melon, and skull plus airsacs). The acoustic intensity distribution and the corresponding polar plots showed that the melon causes the beam to narrow slightly and affects the angle of the main beam. The airsacs kept the sound propagating to the anterior and focused the energy into the main lobe. The bony structure prevented the sound from propagating below the rostrum and contribute to energy in the main beam. The results suggest that the airsacs and the complex bony structure play a dominant role in the formation of the biosonar beam of a dolphin, more so than the melon.
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Simulation of ultrasound beam formation of baiji (Lipotes Vexillifer) with a finite element model
ACOUSTICAL SOC AMER AMER INST PHYSICS, 2014Co-Authors: Wei Chong, Yu Zhang, Au, Whitlow W. L.Abstract:National Science Foundation of China [41276040, 11174240]; Natural Science Foundation of Fujian Province of China [2012J06010]; Fundamental Research Funds for the Central Universities [2011121010]; Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry; China Scholarship CouncilThe baiji (Lipotes Vexillifer) of the Yangtze River possesses a sophisticated biosonar system. In this study, a finite element approach was used to numerically investigate the propagation of acoustic waves through the head of the Yangtze River dolphin, which possesses an inhomogeneous and complex structure. The acoustic intensity distribution predicted from models with and without the melon and/or skull showed that the emitted sound beam was narrow and formed a highly directed acoustic beam, and the skull and melon significantly enhanced the directional characteristics of the emitted sound. Finally, for a short duration impulsive source, the emitted sound pressure distributions were also simulated at different propagation times. The results provide useful information for better understanding the operation of the biosonar system in this rare and perhaps extinct animal. (C) 2014 Acoustical Society of America
Chong Wei - One of the best experts on this subject based on the ideXlab platform.
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Inducing rostrum interfacial waves by fluid-solid coupling in a Chinese river dolphin (Lipotes Vexillifer )
Physical review. E, 2016Co-Authors: Zhongchang Song, Chong Wei, Yu Zhang, Xianyan WangAbstract:Through numerically solving the appropriate wave equations, propagation of biosonar signals in a Chinese river dolphin (baiji) was studied. The interfacial waves along the rostrum-tissue interfaces, including both compressional (longitudinal) and shear (transverse) waves in the solid rostrum through fluid-solid coupling were examined. The baiji's rostrum was found to effect acoustic beam formation not only as an interfacial wave generator but also as a sound reflector. The wave propagation patterns in the solid rostrum were found to significantly change the wave movement through the bone. Vibrations in the rostrum, expressed in solid displacement, initially increased but eventually decreased from posterior to anterior sides, indicating a complex physical process. Furthermore, the comparisons among seven cases, including the combination of (1) the rostrum, melon, and air sacs; (2) rostrum-air sacs; (3) rostrum-melon; (4) only rostrum; (5) air sacs-melon; (6) only air sacs; and (7) only melon revealed that the cases including the rostrum were better able to approach the complete system by inducing rostrum-tissue interfacial waves and reducing the differences in main beam angle and -3 dB beam width. The interfacial waves in the rostrum were considered complementary with reflection to determine the obbligato role of the rostrum in the baiji's biosonar emission. The far-field beams formed from complete fluid-solid models and non-fluid-solid models were compared to reveal the effects brought by the consideration of shear waves of the solid structures of the baiji. The results may provide useful information for further understanding the role of the rostrum in this odontocete species.
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The role of various structures in the head on the formation of the biosonar beam of the baiji (Lipotes Vexillifer)
The Journal of the Acoustical Society of America, 2016Co-Authors: Chong Wei, Zhongchang Song, Yu ZhangAbstract:The relative role of the various structures in the head of the baiji (Lipotes Vexillifer) is examined. A finite element approach was applied to numerically simulate the acoustic propagation through a dolphin's head to examine the relative role of the skull, air sacs, and melon in the formation of the biosonar beam in the vertical plane. The beam pattern obtained with the whole head in place is compared with the beam pattern when the air sac is removed and the other structures (skull and melon) are in place, with only the skull removed, and finally with only the melon removed. The beam pattern with the air sacs and skull intact and the melon removed closely resembled the beam pattern for the complete head, suggesting that the melon has a minor role in the formation of the beam. The beam pattern for the other two cases had very little resemblance to the beam pattern for the whole head. The air sacs seem to have a role of directing propagation of the signal toward the front and the skull prevents the sound propagating below the rostrum. The beam patterns along with a correlation analysis showed that the melon had only a slight influence on the shape and direction of the beam. The resultant beam exiting the head of the dolphin is the result of complex reflection processes within the head of the animal.
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Simulation of ultrasound beam formation of baiji (Lipotes Vexillifer) with a finite element model
The Journal of the Acoustical Society of America, 2014Co-Authors: Chong Wei, Yu ZhangAbstract:The baiji (Lipotes Vexillifer) of the Yangtze River possesses a sophisticated biosonar system. In this study, a finite element approach was used to numerically investigate the propagation of acoustic waves through the head of the Yangtze River dolphin, which possesses an inhomogeneous and complex structure. The acoustic intensity distribution predicted from models with and without the melon and/or skull showed that the emitted sound beam was narrow and formed a highly directed acoustic beam, and the skull and melon significantly enhanced the directional characteristics of the emitted sound. Finally, for a short duration impulsive source, the emitted sound pressure distributions were also simulated at different propagation times. The results provide useful information for better understanding the operation of the biosonar system in this rare and perhaps extinct animal.
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Enhance beam formation by airsacs and skull in Chinese river dolphin (Lipotes Vexillifer)
The Journal of the Acoustical Society of America, 2014Co-Authors: Chong Wei, Zhongchang Song, Yu ZhangAbstract:The melon of dolphins is considered by many as the structure responsible for the focusing of the biosonar beam. However, finite element numerical simulation of the head of the Chinese river dolphin (Lipotes Vexillifer) indicates that the biosonar beam is formed by reflections off the airsacs and bony structures in the skull. The finite element approach was applied to numerically simulate the acoustic propagation through dolphin's head in four several situations (complete head, skull only, skull plus melon, and skull plus airsacs). The acoustic intensity distribution and the corresponding polar plots showed that the melon causes the beam to narrow slightly and affects the angle of the main beam. The airsacs kept the sound propagating to the anterior and focused the energy into the main lobe. The bony structure prevented the sound from propagating below the rostrum and contribute to energy in the main beam. The results suggest that the airsacs and the complex bony structure play a dominant role in the formation of the biosonar beam of a dolphin, more so than the melon.
Tomonari Akamatsu - One of the best experts on this subject based on the ideXlab platform.
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first human caused extinction of a cetacean species
Biology Letters, 2007Co-Authors: Samuel T. Turvey, Tomonari Akamatsu, Xiujiang Zhao, Barbara L. Taylor, Randall R. Reeves, Robert L Pitman, Jay Barlow, Leigh A Barrett, Brent S StewartAbstract: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 multivessel 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).
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estimated detection distance of a baiji s chinese river dolphin Lipotes Vexillifer whistles using a passive acoustic survey method
Journal of the Acoustical Society of America, 2006Co-Authors: Kexiong Wang, Tomonari Akamatsu, Ding Wang, Kaoru Fujita, Rika ShirakiAbstract:Source levels and phonation intervals of whistles produced by a free-ranging baiji (Chinese river dolphin) were measured in the seminatural reserve of Shishou in Hubei, China. A total of 43 whistles were recorded over 12 recording sessions. The mean dominant frequency (the frequency at the highest energy) was 5.7 kHz (s.d.=0.67). The calculated source level was 143.2 dB rms re 1 mu Pa (s.d.=5.8). Most phonation intervals were shorter than 460 s, and the average interval was 205 s (s.d. = 254). Theoretical detection range of baiji's whistle was 6600 m at the present study site, but it could reduce a couple of hundred meters in practical noisy situation in the Yangtze River. Sporadic phonation (205 s interval on average) with relatively faint signal of baiji was considered, to be difficult to be detected by a towing hydrophone system. Stationed monitoring or slow speed towing of hydrophones along the river current is recommended. (c) 2006 Acoustical Society of America.
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echolocation signals of the free ranging yangtze finless porpoise neophocaena phocaenoides asiaeorientialis
Journal of the Acoustical Society of America, 2005Co-Authors: Songhai Li, Ding Wang, Kexiong Wang, Tomonari AkamatsuAbstract: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 μs with an average of 68±14.12 μs. 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 s...
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echolocation range of captive and free ranging baiji Lipotes Vexillifer finless porpoise neophocaena phocaenoides and bottlenose dolphin tursiops truncatus
Journal of the Acoustical Society of America, 1998Co-Authors: Tomonari Akamatsu, D Wang, K Nakamura, K WangAbstract:The interclick intervals of captive dolphins are known to be longer than the two-way transit time between the dolphin and a target. In the present study, the interclick intervals of free-ranging baiji, finless porpoises, and bottlenose dolphins in the wild and in captivity were compared. The click intervals in open waters ranged up to 100–200 ms, whereas the click intervals in captivity were in the order of 4–28 ms. Echolocation of free-ranging dolphins appears to adapt to various distance in navigation or ranging, sometimes up to 140 m. Additionally, the difference of waveform characteristics of clicks between species was recognized in the frequency of maximum energy and the click duration.
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The Yangtze River dolphin or baiji (Lipotes Vexillifer): population status and conservation issues in the Yangtze River, China
Aquatic Conservation: Marine and Freshwater Ecosystems, 2003Co-Authors: Xiao Zhang, Dong Wang, Rui Liu, Zhiyi Wei, Y. Hua, Y. Wang, Z. Chen, Lizhu WangAbstract:1. Baiji were sighted 17 times during three recent simultaneous multi-vessel surveys in the Yangtze River, China (November 4-10, 1997; December 4-9, 1998; October 31-November 5, 1999). There were 11 sightings in 1997 (consisting of 17 animals), five in 1998 (seven animals), and two in 1999 (four animals). It was concluded that 13 individuals Could be considered as a minimum number of the baiji currently in the Yangtze River. 2. An annual rate of population decrease was roughly estimated as 10%. From the body sizes observed, the proportions of old, adult and immature individuals were approximately estimated at 57, 26, and 17% respectively. 3. Baiji showed a significant attraction to confluences and sand bars with large eddies. The present distribution range of the baiji is less than 1400 km in length in the Yangtze main river. Distances between the two nearest groups of baiji appear to be increasing. 4. Two typical sightings are described, in which surfacing and movements of baiji were recorded. Baiji were often found swimming together with finless porpoise. In the surveys they occurred in the same group in 63% of occurrences. Interactions between baiji and finless porpoise are described and discussed. 5. Human activities are the main threats to the baiji. Illegal electrical fishing accounted for 40% of known mortalities during the 1990s. Engineering explosions for maintaining navigation channels have become another main cause of baiji deaths. The last hope of saving the species may be to translocate the remaining baiji into a semi-captive reserve. known as the 'Baiji Semi-natural Reserve'. Copyright (C) 2003 John Wiley Sons, Ltd.