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Lipotes vexillifer
Miller, 1918
English: Yangtse river-dolphin; baiji; whitefin dolphin
German: Chinesischer Flussdelphin
Spanish: Baiji; Delfín de China
French: Baiji; Dauphin de Chine
Family Lipotidae
Lipotes vexillifer © Würtz-Artescienza (see "
links
")
1. Description
The baiji has been the rarest and most endangered cetacean in the world (Smith et al. 2008); it is currently thought to probably be extinct (IUCN, 2009). It was a very graceful animal, with a very long, narrow and slightly upturned beak. The baiji could easily be identified by the rounded melon, longitudinally oval blowhole, very small eyes, low triangular dorsal fin and broad, rounded flippers. The coloration was bluish-grey to grey above and white to ashy-white below. Females were larger than males, reaching 253 cm as opposed to 229cm (Zhou, 2002).
2. Distribution
The baiji was an exclusively freshwater species and ranged in the lower and middle reaches of the Chang Jiang (Yangtze River), from its estuary upstream for 1,600 km as far as the gorges above Yichang (20m above sea level). At least one record was reported from the lower Fuchun Jiang at Tonglu (Rice, 1998). Individuals may have entered some tributary lakes during intense flooding (Zhou, 2002).
Distribution of the possibly extinct Lipotes vexilifer in the Chang Jiang (Yangtse River) and its
tributaries (Smith et al. 2008 © IUCN;
enlarge map
).
3. Population size
Zhou et al. (1998) report that boat surveys conducted along a 500km section of the Yangtze River between Zhenjiang and Hukou in 1989-1991 resulted in identification of seven individual baiji based on natural markings. There were 7 sightings of baiji in May 1989, 4 sightings in March 1990 and 6 sightings in April-May 1990, resulting in an estimated population size of about 30 individuals in the 500-km river study area. If the baiji was still inhabiting its historical 1,600 km range in the Yangtse River, and population density was similar throughout this habitat section, there may have been 100 baiji left in the river at that time.
However, results of subsequent surveys of almost all the species' previous range, Shanghai to Yichang, suggested that the population was very small and in further decline. In 1998 only a few dozen animals may have still been alive (Zhou, 2002). From observations between 1997-1999, Zhang et al. (2003) concluded that 13 individuals could be considered as a minimum number of the baiji in the Yangtse River at that time. The annual rate of population decrease was roughly estimated as 10%. The distribution range of the baiji was less than 1,400 km in length in the Yangtze main river. Distances between the two nearest groups of baiji appeared to be increasing.
In Dongting Lake and Boyang Lake, the baiji became extinct by 1999 (Yang et al. 2000). Finally, 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 (Turvey et al. 2007). The authors concluded 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. There are no baiji in either natural reserves or in dolphinariums (Smith et al. 2008).
4. Biology and Behaviour
Habitat
: Baiji were generally found in eddy countercurrents below meanders and channel convergences. The Yangtze River is turbid, and visibility from the surface downward is about 25-35cm in April and 12cm in August. Baiji eyes were correspondingly reduced, much smaller than those of other dolphins and placed higher on the head. However, they were functional, and baiji could distinguish objects placed on the surface (Zhou, 2002). Zhang et al. (2003) reported that baiji showed a significant attraction to confluences and sand bars with large eddies.
Schooling
: They generally lived in small groups of 3-4 animals, largest observed group size being 16 animals (Zhou, 2002). Two typical sightings are described (Zhang et al. 2003), in which surfacing and movements of baiji were recorded. Baiji were often found swimming together with finless porpoises. In the surveys they occurred in the same group in 63% of occurrences.
Behaviour: Baiji would surface without splashing and breathe smoothly. Short breathing intervals of 10-30s alternated with a longer one of up to 200s (Zhou, 2002).
Reproduction
: The baiji probably bred and gave birth in the first half of the year. The peak calving season appeared to be February to April (Zhou, 2002).
Food
: Any available species of freshwater fish was taken, the only selection criterion appears to have been size (Zhou, 2002).
5. Migration
Reyes (1991) classified the species as "non-migratory". Peixun (1989) reported movements within home ranges but not migratory behavior. However, baiji also made long-range movements. Hua et al. (1994) recorded a single individual moving more than 300 km from March 1989 to January 1992, implying that the baiji's distribution range may have been dynamic. Anecdotal information from fishermen in the river during the surveys indicated that baiji moved upstream when water rose in the spring and downstream when water receded in winter (Zhang et al. 2003).
Zhou et al. (1998) showed from photographic identifications and sighting records that baiji groups made both local and long-range movements. The largest recorded movement of a recognisable baiji was 200+ km from the initial sighting location.
6. Threats
As summarized by Zhou (2002), the threats faced by the baiji included river traffic, fishing gear, reduction of fish stocks, and water pollution. Zhang et al. (2003) added to this list illegal electrical fishing, accounting for 40% of known mortality during the 1990s, and engineering explosions for maintaining navigation channels, which became another main cause of baiji deaths.
Furthermore the Yangtze was suffering massive habitat degradation that likely added to the onset of the baiji's demise:
- The banks of the river have been modified extensively to prevent destructive flooding of agricultural areas, thus reducing the floodplain area (Zhou, 2002).
- Wastewater volume discharged into the Yangtze is about 15.6 billion cubic meters per year. Approximately 80% of these wastewaters are discharged directly into the environment without treatment (Zhou, 2002).
- Dudgeon (1995) reported that in the Zhujiang, dam construction has caused reductions in fisheries stocks but here, as elsewhere in China, the ecologically damaging consequences of river regulation are exacerbated by overfishing and increasing pollution of rivers by sewage, pesticides and industrial wastes. o In addition, deforestation and soil erosion in the Chang Jiang basin have given rise to siltation and degradation of floodplain habitats (Dudgeon, 1995).
Finally, Rosel and Reeves (2000) pointed out another, equally threatening effect. These animals faced an additional suite of potentially serious problems that were often overlooked, perhaps because they were not so obvious. The genetic and demographic consequences associated with very small population size can result in extinction even when effective measures are in place to protect the animals and their habitat. Small populations tend to harbor less genetic variation than large populations. In addition, small populations are more strongly affected by processes of genetic drift and inbreeding, both of which can further reduce genetic variability. Genetically depauperate populations may have lower fitness, a reduced ability to adapt to changes in their environment over time, and decreased evolutionary potential. Finally, small populations may also be more vulnerable to demographic stochasticity, which can accelerate the process of extinction. Awareness of the genetic and demographic consequences of small population size should be integral to planning for conservation of endangered river cetacean species and populations.
7. Remarks
Range state
(Smith et al. 2009): China
Huan and Chen reported as early as 1992 that "the distribution density of baiji in the river section of Ouchikou-Chenglingji (158 kilometres) was gradually diminishing. Its distribution density in the section under research diminished from 3.67 km/per dolphin in 1986 to 10.36 km/per dolphin in 1991. The baiji has been listed as First-Class Animal under the protection of the Chinese Government, but its population size decreases further and human activities still severely endanger its existence. With further human exploitation of the Yangtse River, new key water-control projects will be built. Hence, a conservation strategy must be adopted to rescue this species."
The IUCN lists the species as "critically endangered and possibly extinct" (C2a(ii); D). It was a relict species and the only living representative of the family Lipotidae and met the definition of a Critically Endangered (CR) species, as it is facing an extremely high risk of extinction in the wild (Smith et al. 2008).
L. vexilifer
is listed in appendices I and II of CITES. Because it was not an internationally migrating species, it was not listed by CMS.
8. Sources
· Dudgeon D (1995) River regulation in southern China: Ecological implications, conservation and environmental management. Regulated Rivers Research & Management 11(1): 35 - 54
· Hua Y, Gao S, Zhang J. 1994. Population size of baiji and the analysis of the population decreasing. In Working Paper on Baiji Population and Habitat Viability Assessment Workshop Report, Zhou K, Ellis S, Leatherwood S, Bruford M, Seal US (eds), 41-45.
· Huan Y, Chen P (1992) Investigation for impacts of changes of the lower reach of Gezhou Dam between Yichang and Chenglingji on the baiji,
Lipotes vexillifer vexillifer
after its key water control project founded. J Fish China Shuichan Xuebao. 16(4): 322-329
· Peixun (1989) Baiji - Lipotes vexilifer. In: Handbook of Marine Mammals (Ridgway SH, Harrison SR eds.) Vol. 4: River Dolphins and the Larger Toothed Whales. Academic Pres, London, pp. 25 - 44.
· Reyes JC (1991) The conservation of small cetaceans: a review. Report prepared for the Secretariat of the Convention on the Conservation of Migratory Species of Wild Animals. UNEP / CMS Secretariat, Bonn.
· Rice DW (1998) Marine mammals of the world: systematics and distribution. Society for Marine Mammalogy, Special Publication Number 4 (Wartzok D, Ed.), Lawrence, KS. USA.
· Rosel PE, Reeves RR (2000) Genetic and demographic considerations for the conservation of Asian river cetaceans. In: Reeves, RR (ed); Smith, BD (ed); Kasuya, T (ed). Biology and conservation of freshwater cetaceans in Asia. 23: 144-152
· Smith BD, Zhou K, Wang D, Reeves RR, Barlow J, Taylor BL, Pitman R (2008)
Lipotes vexillifer
. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>.
· Turvey ST, Pitman RL, Taylor BL, Barlow J, Akamatsu T, Barrett LA, Zhao X, Reeves RR, Stewart BS, Wang K, Wei Z, Zhang X, Pusser LT, Richlen M, Brandon JR, Wang D (2007) First human-caused extinction of a cetacean species? Biol Lett 3: 537-540
· Zhang, X, Jiang G, Jiang X, Li Y (2001) Impacts on baiji and finless porpoise by some projects of preventing and controlling flood in the Yangtze River, with conservation strategies. Resour Environ Yangtze Basin 10: 242-246
· Zhou K (2002) Baiji -
Lipotes vexilifer
. In: Encyclopedia of marine mammals (Perrin WF, Würsig B, Thewissen JGM, eds.) Academic Press, San Diego, 58 - 61.
· Zhou K, Sun J, Gao A, Wuersig B. (1998) Baiji (
Lipotes vexillifer
) in the lower Yangtze River: Movements, numbers, threats and conservation needs. Aquatic.Mammals. 24(2):123-132
· Yang J, Xiao W, Kuang X-A, Wei Z, Liu R-J (2000) Studies on the distribution, population size and the active regularity of
Lipotes vexillifer
and
Neophocaena phocaenoides
in Dongting Lake and Boyang Lake. Resour Environ Yangtze Basin 9: 443-450
· Zhang X, Wang A, Liu R, Wei Z, Hua Y, Wang Y, Chen Z, Wang L (2003) TheYangtze River dolphin or baiji (
Lipotes vexillifer
): population status and conservation issues in theYangtze River, China. Aquatic Conserv: Mar. Freshw. Ecosyst. 13: 51-64
© Boris Culik (2010) Odontocetes. The toothed whales: "
Lipotes vexillifer
". UNEP/CMS Secretariat, Bonn, Germany. http://www.cms.int/reports/small_cetaceans/index.htm
© Illustrations by Maurizio Würtz, Artescienza.
© Maps by IUCN.
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