Chinese River Dolphin / Baiji (Lipotes vexillifer)
Did You Know?
· This dolphin is the rarest species of all marine mammals; many scientists fear that it is functionally extinct. A recent extensive survey of this species resulted in no sightings.
|Weight:||500 pounds (220 kg)|
|Length:||8 ft (2.5 m)|
|Appearance:||pale blue to gray on their back and white on the under side|
|Lifespan:||about 25 years (based on an individual in captivity)|
|Diet:||large variety of freshwater fish species|
|Behavior:||very little is known about the behavior, but they depend largely on underwater sound for orientation, feeding, and communication and, just like most dolphin species, they produce clicks and whistles|
The Chinese river dolphin is a freshwater dolphin and one of the most endangered animals on Earth. It is also known as the Yangtze river dolphin, baiji, white-flag dolphin, and white-fin dolphin. Nicknamed "Goddess of the Yangtze," it was regarded as the goddess of protection by local fishermen and boatmen in China (Zhou, 1991).
The Yangtze river dolphin is pale blue to gray on the dorsal (back) side, white on the ventral (belly) side. It has a long and slightly-upturned beak with 31-36 conical teeth on either jaw. Its dorsal fin is low and triangular in shape, and resembles a light-colored flag when the dolphin swims just below the surface of the murky Yangtze River, hence the name "white-flag" dolphin. It has smaller eyes compared to oceanic dolphins. A mature Yangtze river dolphin is about 8 ft (2.5 m) long and weighs about 500 pounds (220 kg).
Though it has been described in classical Chinese literature and folklore as early as 200 B.C., the Yangtze river dolphin was not known to the western world until 1916, when Charles M. Hoy, the son of an American missionary, shot one while duck hunting on Dongting Lake, China (Zhou, 1991). Subsequently, this species was formally introduced to the scientific community by Gerrit S. Miller, Jr., a curator at the Smithsonian Institute's National Museum of Natural History.
Just like the other species of river dolphins (the Amazon river dolphin, Inia geofrensis; the La Plata river dolphin, Pontoporia blainvllei; and the Indian river dolphin, Platanista gangetica), the Yangtze river dolphin originated from the ocean. The ancestor of the Yangtze river dolphin resided in the shallow sea that inundated the Yangtze River Basin during the globally high sea levels of the Middle Miocene period (approximately 20 million years ago). After the subsequent sea-level lowering and transition to a freshwater river during the late Neogene period, the dolphins remained and evolved to become the present-day Yangtze river dolphins (Hamilton et al., 2001).
The Yangtze river dolphin is thought to breed in the first half of the year, with the peak calving season between February and April. Gestation lasts 10-11 months, and a newborn calf measures about 3 feet (1 m). Dolphins reach sexual maturity at 4-6 years of age (Zhou, 2004). The life expectancy for the Yangtze river dolphin is about 25 years, based on an individual in captivity.
Very little is known about the ecology, behavior, and acoustics of the Yangtze river dolphin. Groups of two to six animals were most commonly seen, although aggregations of up to 16 animals have also been observed (Zhou, 2004). The Yangtze river dolphin feeds on a large variety of freshwater fish species (Zhou, 2004). These dolphins are generally shy of boats, and often expose only the top of the head, dorsal fin, and a small part of the back when surfacing (Zhou, 2004).
Due to the poor visibility in the murky Yangtze River, the Yangtze river dolphin depends largely on underwater sound for orientation, feeding, and communication. Just like most dolphin species, the Yangtze river dolphin produces two types of sounds: clicks and whistles (Akamatsu et al., 1998; K. Wang et al., 2006a). Clicks are believed to be used primarily for navigation and identifying prey and other objects in the surrounding environment (Au, 1993). Whistles are frequency modulated (pitch changes with time) sounds and are thought to be used for communication. (K. Wang et al., 2006a)
Chinese River Dolphin Range Map
(click for larger view PDF)
Historically, the species occurred in the middle to lower reaches of the Yangtze River, along with its tributaries and connecting lakes in China (Zhou et al., 1977). Due to habitat loss caused by rapid development along the Yangtze River, its distribution was largely reduced. More recently, it is believed that the Yangtze river dolphin is limited to the main channel of an 870-mile (1,400-km) river section between Jingzhou and Jiangyin (Zhang et al., 2003).
No historical population estimate of the Yangtze river dolphin is available. However, the population of the Yangtze river dolphin has declined drastically and rapidly since the 1950s (Zhou et al., 2004; Turvey et al., 2007). The estimated population size declined to 400 by the 1980s (Zhou et al., 1982). Surveys conducted between 1997 and 1999 led scientists to believe that the minimum number left in the Yangtze could be as low as 13 individuals (Zhang et al., 2003). The last authenticated Yangtze river dolphin records were of a stranded pregnant female found in 2001, and a live animal photographed in 2002 (Turvey et al., 2007). In 2003, a report published by the Chinese Institute of Hydrobiology concluded that the population is probably declining by about 10% per year, suggesting that extinction would occur within a decade (Zhang et al., 2003).
During November and December 2006, an international research team, including biologists from NOAA's National Marine Fisheries Service, conducted an intensive six-week multi-vessel visual and acoustic survey covering the entire historical range of the Yangtze river dolphin in the main Yangtze channel between Yichang and Shanghai (1,669 km). By the end of the expedition, the team failed to find any evidence that the species survives, and concluded that the Yangtze river dolphin may now be extinct (Turvey et al., 2007).
- bycatch in local fisheries, which use rolling hooks, nets (gillnets and fyke nets), and electro-fishing (Zhou and Wang, 1994; Zhou et al., 1998).
- Rolling hooks and other fishing gear caused at least half of all known dolphin deaths in the 1970s and 1980s.
- Electro-fishing accounted for 40% of dolphin deaths recorded during the 1990s (Lin et al., 1985; Chen and Hua, 1989; Zhou and Li, 1989; Zhou and Wang, 1994; Zhou et al., 1998; Zhang et al., 2003).
Other threats to the Yangtze river dolphin include (K. Wang et al., 2006b)
- river development projects
- vessel collision
- underwater explosions used to deepen or widen navigation channels or used for illegal fishing are another cause of dolphin mortality.
Zhou and Li (1989) once reported that explosions caused 19.4% of deaths during illegal fishing operations (using explosives) in the lower reaches of the river between 1979 and 1981.
The increasing rate of water project development, including construction of dams and floodgates in the middle and lower reaches of the Yangtze, has resulted in blockages between the river and the lakes. The dams interrupted the movements of the Yangtze river dolphins upstream of the dams, and eliminated their access to tributaries and appended lakes (Chen and Hua, 1989; Liu et al., 2000). These dams also caused a notable decline in fish resources (Zhou and Li, 1989). The world's largest dam, the Three Gorges Dam, has been inserted in the middle of a hot spot of bio-diversity in south-central China, which affected the habitats of the Yangtze river dolphin (Chen et al., 1997 in K. Wang et al., 2006b; Zhou, 1991).
Five natural reserves have been established along the middle and lower reaches of the Yangtze River since 1986 for the protection of the Yangtze river dolphin, and another rare cetacean species, the Yangtze finless porpoise (Wang et al., 2006). However, these reserves do not prevent the incidental death of these species (D. Wang et al., 2006; K. Wang et al., 2006b).
In addition to these natural reserves, two semi-natural reserves were established for the purpose of housing Yangtze river dolphins under human management (Baiji Research Group, 1989; Zhou, 1989). However, neither semi-natural reserve has ever been used for captive propagation of the Yangtze river dolphins. In 1980, a male Yangtze river dolphin was rescued from fishing gear and rehabilitated in Baiji Dolphinarium at the Institute of Hydrobiology of Chinese Academy of Science in Wuhan (Gui and Wang, 2005; Chen and Liu, 1989). This dolphin died from old age in 2002 after more than 22 years in captivity (K. Wang et al., 2006b).
In response to the dramatic and rapid decline of the Yangtze river dolphin and other wildlife species between 1985 and 1987, the Chinese Government issued the "Circular for the Protection of Precious and Rare Wildlife" and the "Urgent Circular Banning Hunt, Trade, and Smuggling of Precious and Rare Animals," making the protection of these species a law (Zhou and Zhang, 1991). Subsequently, the Yangtze river dolphin was designated as one of the "First Category of National Key Protected Wildlife Species" in China (K. Wang et al., 2006b).
In the United States, all marine mammals, including Yangtze river dolphins, are protected under the Marine Mammal Protection Act (MMPA), as amended. In addition, this species is also listed as endangered species under the Endangered Species Act of 1973 and depleted under the MMPA.
|ESA Listing Rule||54 FR 22906||05/30/1989|
- NMFS Southwest Fisheries Science Center Chinese River Dolphin Project
- NMFS National Marine Mammal Laboratory River Dolphin Information
- U.S. Fish & Wildlife Service Chinese River Dolphin Species Profile
- Scientists Fear Rare Dolphin Driven to Extinction by Human Activities, Other Species Also Vulnerable [pdf] (September 2007 Press Release)
- IUCN Chinese River Dolphin Species Information
- Ocean Biogeographic Information System (OBIS-SEAMAP) Chinese River Dolphin Species Profile
- Akamatsu, T., D. Wang, K. Nakamura and K. Wang. 1998. 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 104(4):2511-2516.
- Baiji Research Group. 1989. A proposal for establishment of a semi-natural reserve at Shishou for conservation and management of the baiji (Lipotes vexillifer). Pp 21-22. In: W. Perrin, R. Brownell, K. Zhou and J. Liu (eds.). Biology and Conservation of the River Dolphins. World Conservation Union, Gland, Switzerland.
- Chen, P., and R. Liu. 1989. Captive husbandry of the baiji, Lipotes vexillifer. Pp 146-149. In: W. Perrin, R. Brownell, K. Zhou and J. Liu (eds.). Biology and Conservation of the River Dolphins. World Conservation Union, Gland, Switzerland.
- Chen, P., and Y. Hua. 1989. Distribution, population size and protection of Lipotes vexillifer. Pp 81-85. In: W. Perrin, R. Brownell, K. Zhou and J. Liu (eds.). Biology and Conservation of the River Dolphins. World Conservation Union, Gland, Switzerland.
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- Lin, K., P. Chen and Y. Hua. 1985. Population size and conservation of Lipotes vexillifer. Acta Zoologica Sinica 5:77-85.
- Liu, R., D. Wang and K. Zhou. 2000. Effects of water development on river cetacean in China. Pp 40-42. In: R.R. Reeves, B.D. Smith, and T. Kasuya (eds.). Biology and Conservation of Freshwater Cetaceans in Asia. IUCN SSC Occasional Paper No. 23, IUCN, Gland, Switzerland and Cambridge, UK.
- Turvey, S.T., R.L. Pitman, B.L. Taylor, J. Barlow, T. Akamatsu, L.A. Barrett, X. Zhao, R.R. Reeves, B.S. Stewart, K. Wang, Z. Wei, X. Zhang, L.T. Pusser, M. Richlen, J.R. Brandon and D. Wang. 2007. First human-caused extinction of a cetacean species? Biology Letters. published online doi:10.1098/rsbl.2007.0292.
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- Wang, K., D. Wang, T. Akamatsu, K. Fujita and R. Shiraki. 2006a. 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 120(3):1361-1365.
- Wang, K., D. Wang, X. Zhang, A. Pfluger and L. Barrett. 2006b. Range-wide Yangtze freshwater dolphin expedition: the last chance to see baiji? Environmental Science and Pollution Research 13(6):418-424.
- Zhang, X., D. Wang, R. Liu, Z. Wei, Y. Hua, Y. Wang, Z. Chen, and L. Wang. 2003. The Yangtze River dolphin or baiji (Lipotes vexillifer): population status and conservation issues in the Yangtze River, China. Aquatic Conservation: Marine and Freshwater Ecosystem. 13: 51-64.
- Zhou, K. 1989. Progress report on the semi-natural reserve at Tongling. Pp 19-20. In: W. Perrin, R. Brownell, K. Zhou and J. Liu (eds.). Biology and Conservation of the River Dolphins. World Conservation Union, Gland, Switzerland.
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- Zhou, K., and X. Wang. 1994. Brief review of passive fishing gear and incidental catches of small cetaceans in Chinese waters. Reports of the International Whaling Commission Special Issue 15:347-354.
- Zhou, K., and X. Zhang. 1991. Baiji: The Yangtze River Dolphin and Other Endangered Animals of China (Translated by C. Luo). Yilin Press, Nanjing, China.
- Zhou, K., W. Qian and Y, Li. 1977. Studies of the distribution of baiji, Lipotes vexillifer Miller. Acta Zoologica Sinica 23:72-79 (in Chinese with English abstract).
- Zhou, K., Y. Li, M. Nishiwaki and T. Kataoka. 1982. A brief report on observations of the baiji (Lipotes vexillifer) in the lower reaches of the Yangtze River between Nanjing and Guichi. Acta Theriologica Sinica 2:253-254.
- Zhou, K., J. Sun, A. Gao and B. Würsig. 1998. Baiji (Lipotes vexillifer) in the lower Yangtze River: movements, numbers threats and conservation needs. Aquatic Mammals 24(2):123-132.
Updated: December 5, 2012