Monday, 13 December 2010

Humans cause new extinction record

A visual and acoustic survey of the Yangtze River dolphin (Lipotes vexillifer) confirms the first human-induced extinction of a large vertebrate species for over 50 years.

The Yangtze River dolphin (Fig.1), more commonly referred to as the baiji or the “Goddess of the Yangtze” is an obligate freshwater odontocete or toothed whale. Its distribution is exclusive to the middle-lower region of the Yangtze River, with records of sightings expanding into the neighbouring Qiantang River of eastern China.
The baiji has long been considered to be one of the rarest and most threatened mammal species on the planet, suffering from a rapid population decline. A recent study by Turvey et al1 failed to detect the presence of the baiji, using systematic visual and acoustic surveys ranging from Yichang to Shanghai (Fig.2). This has led to the unfortunate conclusion that the Yangtze River dolphin has most likely been driven to extinction.


Figure 1. The Yangtze River Dolphin/baiji (Lipotes vexillifer)10


In 2001, the IWC listed the baiji as the most endangered cetacean on the planet2. It previously occurred as far upstream as Tonglu in the Fuchun river3. Its distribution was gradually reduced from a 1000 mile stretch of the middle-lower Yangtze to just 150km of the main channel, as depicted in figure 2, between the tributary lakes of Dongting and Poyang4. Approximately 12% of the world’s human population live in the Yangtze region, and this has led to extreme ecological pressure and deterioration5. Habitat loss has been caused largely due to the construction of the three gorges dam, along with other small-scale damming developments.
There have been ongoing surveys documenting the dramatic decline of the baiji. The population declined from an estimated 400 in 19816 to 13 in 19997. The People’s Republic of China declared the baiji endangered in 1979, but only made baiji hunting illegal in 1983, by which point the population had already collapsed to just 300 individuals. Throughout this time, the development of dams led to severe habitat and species loss along the river, most notably by the Gezhouba Dam (1989) and the Three Gorges Dam (1994). The IUCN listed the species as critically endangered by 1996, with the last recorded sighting occurring in 2004. 
Figure 2. A map of the survey route from Turvey et al1
covering the historical distribution of the baiji in the main channel of the Yangtze River. 


Baiji fatalities have been somewhat attributable to direct injuries from entanglement in fishing gear (predominantly rolling hooks), electrocution from electric fishing, hunting, underwater blasting for channel maintenance and collisions with vessels. In addition to this, industrialisation has led to tributary damage, dredging, overfishing, vessel traffic and drainage for land reclamation, causing a severe ecological deterioration of the region5. It is believed that the primary cause of the baiji decline has been due to unsustainable by-catch in local fisheries, which employ damaging fishing practices. Despite legislation, these harmful unselective fishing techniques remain ubiquitous1.
There was a general consensus amongst scientists that the best management strategy would be to combine in-situ and ex-situ conservation efforts, in order to preserve the habitat as well as raise a large enough population to be re-introduced. Conservation strategies were implemented from the 1980s, with attempts to capture dolphins for relocation to reserves. These efforts, however, were largely unsuccessful as the capture of the quick dolphins proved to be difficult, and those that were caught had low captive survival rates. Five protected reserves were established along the Yangtze in 1992; however this covered just 1/3 of the baiji’s natural habitat range and had limited success8. It was very much a case of too little too late, and as August Pfluger of the Baiji Foundation said in 2006; “The strategy of the Chinese government was a good one, but we didn’t have time to put it into action”.
It is clear that anthropogenic factors have driven the baiji to extinction, and this threatens to have similar effects on other freshwater cetaceans, in particular the Yangtze finless porpoise (Neophocaena phocaenoides)5. The Chinese paddlefish (Psephurus gladius) is a sturgeon which is also at risk of extinction because of the Yangtze River deterioration7. However, this is a world-wide issue and some of the most critically endangered species on the planet are currently threatened because of unsustainable fishing practices (e.g. the Gulf of California porpoise, Phocoena sinus1). The Yangtze River dolphin was one of five freshwater dolphins on the planet. The remaining four are the Amazon River dolphin (Inia geoffrensis), the La Plata River dolphin (Pontoporia blainvillei), the Ganges River dolphin (Platanista gangetica) and the Indus River dolphin (Platanista minor). River dolphins, in particular the La Plata River dolphin are all at risk of extinction because of habitat loss and hunting9. The baiji represented the only recent species from the Lipotidae clade, having diverged from other cetacean lineages in excess of 20 million years ago9.
The Baiji extinction denotes a significant loss of mammalian evolutionary history. It marks the fourth disappearance of an entire mammal family since AD 1500, the first global extinction of a megafaunal vertebrate in half a century, the first species extinction of a charismatic vertebrate of conservation interest and the first cetacean species to have been driven to extinction by human activity. An impressive record, but for all the wrong reasons. The extinction of the remarkable Yangtze River dolphin serves as a crucial reminder that continuous conservation efforts and interventions remain pertinent if we are to sustain the biodiversity that we enjoy today.

1. Turvey, S.T., Pitmann, R.L., Taylor, B.L., Barlow, J., Akamatsu, T., Barrett, L.A., Zhao, X., Reeves, R.R., Stewart, B.S., Wang, K., Wei, Z., Zhang, X., Pusser, L.T., Richlen, M., Brandon, J.R. & Wang, D. (2007). First human-caused extinction of a cetacean species? Biol. Lett. 3, 537-540.
2. IWC. (2001). Report of the standing sub-committee on small cetaceans. Journal of Cetacean Research and Management. 3 (Supplement), 263–291.
3. Zhou, K., Qian, W., and Li, Y. 1977. Studies on the distribution of baiji, Lipotes vexillifer Miller. Acta Zoologica Sinica 23, 72–79. [In Chinese; English summary.]
4. Reeves, R.R., Smith, B.D., Crespo, E.A. & Notarbartolo di Sciara, G. (2003). Dolphins, Whales and Porpoises: 2002-2010 Conservation Action Plan for the World’s Cetaceans. IUCN/SSC Cetacean Specialist Group. IUCN, Glad, Switzerland and Cambridge, U.K.
5. Zhou, K., Sun, J., Gao, A. & Würsig, B. (1998). Baiji (Lipotes vexillifer) in the lower Yangtze River: movements, numbers threats and conservation needs. Aquat. Mamm. 24(2), 123–132.
6. Zhou, K., Li, Y., Nishiwaki, M. & Kataoka, T. (1982). A brief report on observations of the baiji (Lipotes vexillifer) in the lower reaches of the Yangtze River between Nanjing and Guichi. Acta Theriol. Sin. 2, 253–254.
7. Zhang, X., Wang, D., Liu, R., Wei, Z., Hua, Y., Wang, Y., Chen, Z. & Wang, L. (2003). The Yangtze River dolphin or baiji (Lipotes vexillifer): population status and conservation issues in the Yangtze River, China. Aquat. Conserv. Mar. Freshw. Ecosyst. 13, 51–64.
8.Wang, D., Zhang, X., Wang, K., Wei, Z., Würsig, B., Braulik, G. & Ellis, S. (2006). Conservation of the Baiji: No Simple Solution. Conservation Biology. 20(3), 623-625.
9. Isaac, N.J.B., Turvey, S.T., Collen, B., Waterman, C. & Baillie, J.E.M. (2007). Mammals on the EDGE: conservation priorities based on threat and phylogeny. PLoS ONE.2(3), e296.
10. James, D. (2003). Limassol Link Photo Gallery. [Date Accessed: 01/12/10: http://www.limassollink.com/4images/details.php?image_id=864]

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