A six-week survey of the Yangtze River’s middle and lower stretches by the Chinese Academy of Sciences’ Institute of Hydrobiology (IHB) in Wuhan and the conservation group WWF in China has concluded that the Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis) are being driven to the brink of extinction by fishing, pollution and other human activities.
The final results will be announced in March, but the preliminary findings are worrisome to scientists. The survey team spotted fewer than half of the N. p. asiaeorientalis that were seen during a similar fact-finding expedition in 2006 that found 1,225 living in the river¹.
N. p. asiaeorientalis is doing much worse than previously thought. N. p. asiaeorientalis is one of the few extant freshwater cetaceans and it is only found in the Yangtze, as well as two adjoining lakes, the Poyang and the Dongting. Scientists hope that the species can avoid the fate of the Yangtze river dolphin (Lipotes vexillifer), which was declared effectively extinct after the 2006 survey¹.
There are 450 N. p. asiaeorientalis in Poyang Lake, and that population has been stable for the past six years. Only 90 remained in Dongting Lake, which is a decline of 40%. This means that there are only about 1,000 finless porpoises in the Yangtze River basin.
Intense human activity is to blame, states Lei Gang, director of the WWF China’s freshwater program. Overfishing has caused a big decline in the porpoises’ natural food source. The animals are also vulnerable to unregulated fishing methods, like electro-fishing, which sends electrical currents into the water to stun fish before they are caught.
The Yangtze supports 40% of China’s population, and most of its banks are lined with large cities, factories and power plants. This causes 20 billion tonnes of waste to be discharged into the Yangtze every year. This estimate doesn’t even include diffuse pollution from agriculture or pollution caused by ships.
N. p. asiaeorientalis uses sonar for navigation, ranging and foraging. The high density of ships along the Yangtze creates high levels of acoustic pollution, which interferes with the animals’ sonar. This affects their feeding and many are also wounded and die because of collisions with ships.
The new estimate will probably make N. p. asiaeorientalis join the critically endangered list of the IUCN. They were already endangered. Within 15 years, they might be completely extinct.
- Zhao, X. et al. Biol. Conserv. 141, 3006–3018 (2008).