The Demise of the Yangtze Finless Porpoise

This is an image of a map of the Yangtze River, showing its course and the area covered.
Figure 1-Map of the Yangtze River, China, that flows for 6,418km (3988 miles) long http://www.discoveryangtze.com/Yangtzediscovery/map/mapyangtze.jpg

The Yangtze River is the longest river in Asia and the third longest river in the world. The river runs from the glaciers in Qinghai eastward across China emptying out into the East China Sea at Shanghai, (see Fig.1). It also has one of the largest river discharge volumes in the world, with an average discharge of 29,400 m3/s, (Müller et al., 2008). Within its waters is the world’s only freshwater porpoise, the Yangtze finless porpoise, Neophocaena asiaeorientalis, (see Fig. 2). It is the only member of the family, Phocoenidae, without a dorsal fin. They can reach a length of 2.27m, and have a known body mass of 71.8 kg, (Kasuya, 1999). The porpoise feeds on small fishes, cephalopods, and crustaceans, (Jefferson and Hung, 2004). They have an average lifespan of 20 – 30 years. Individuals have extended upriver to Yichang, in the upper region, (Zhang et al., 1993), but are mainly found in the lower-middle regions of the river, (Zhao et al., 2008).   The porpoise was listed as Endangered by International Union for Conservation of Nature (IUCN) in 1996, (Baillie and Groombridge, 1996). It appears to be rapidly declining towards extinction. In the early 1990’s, it was estimated that there were around 2700 porpoises, (Zhang et al.,1993), however the total estimate was found to be approximately 1800 porpoises in Nov and Dec 2006, (Zhao et al., 2008). This is an annual rate of decline of at least 5%. However, recent scientific research revealed there were only 1,000 left in China in 2012, declining by an average of 13.7% each year. It is believed that the animal will become extinct in 5 to 10 years.

 

This is an image showing the physical appearance of the Yangtze Finless Porpoise.
Figure 2-Yangtze Finless Porpoise http://www.news.bbcimg.co.uk/media/images/65620000/jpg/_65620858_02.jpg

This decline may be due to recent human development, over the past thirty years, due to China’s rapidly growing economy and population, such as dams. China has over 86,000 dams, the largest number of dams within a country in the world (National geographic, 2010). The Three Gorges Dam, the largest hydroelectric powered dam is located in Yichang, in the upper region of the Yangtze River, (see fig.3). Water development projects, can cause problems for the porpoises as they can block their movements between the river, lakes and tributaries, (Liu et al., 2000; Smith and Reeves, 2000), and of their prey, (Xie and Chen, 1996), and can also change downstream environmental conditions, (Tong et al., 2008). However, the Chinese government’s Yangtze River Water Resources Committee says, water qualities upstream of the dam have remained unchanged since natural water flow was stopped in 2003.

This image shows the Three Gorges Dam in the background with masses of waste floating and being washed up on the shore of the Yangtze River in the foreground.
Figure 3-Three Gorges Dam and the heavily polluted Yangtze River http://www.theepochtimes.com/n2/images/stories/large/2010/09/02/103228017Yangtze.jpg

Four hundred million people and thousands of factories are situated in the Yangtze River basin releasing tremendous amounts of domestic sewage and industrial emissions into the waterways, (see fig. 3). The river is only a relatively small body of water in comparison to the amount of pollution which is expelled into it; therefore the water quality can be degraded much more easily. There is little data that has assessed the impacts of pollutants on Yangtze finless porpoise overall health. However, between 1998 and 2004, five finless porpoises died accidentally in the Eastern Dongting Lake. The Mercury concentrations in some key tissues were measured and found that the highest total mercury level concentrations in liver and kidney were both found in a 2-month-old calf, which implied that the transfer effiency of mercury from mothers to their young in the porpoise is remarkable. It seems that the Yangtze finless porpoise in Eastern Donating Lake had much higher total mercury levels than those reported for other Phocoenidae species, (Dong et al., 2006).

Besides chemical pollution, there is also noise pollution, due to the high-density of large cargo vessels in the Yangtze River, (see fig. 4), approximately one ship every 100m, (Zhao et al., 2008). The finless porpoise has a less specific sensitivity to sound compared with other Phocoenidae, (Woods Hole Oceanographic Institution, 2013), so when combined with boat traffic and noise, it can mask their social communication and their ability to forage, (Wang et al., 2006). Vast numbers of ships can likely cause mortality of finless porpoises from propeller strikes. Therefore, finless porpoises have been previously reported to prefer habitat near the river banks (Wei et al., 2003; Zhang et al., 1993). This might be due to a certain amount of boat avoidance behaviour, (Li et al., 2008). Such behaviour has also been observed in surveys of harbour porpoises, (Palka and Hammond, 2001).

The image shows a large number of cargo vessels on the Yangtze River.
Figure 4-Ships on the Yangtze River http://thewatchers.adnorraeli.com/wp-content/uploads/2011/05/f04da2db14840f35eb7505.jpg

A high number of vessels are cargo ships, however with China’s vast growing population; a large majority are fishing boats. In the Yangtze River, there is widespread illegal fishing, (Reeves et al., 2000; IWC, 2001; Smith et al., 2007). The preferred habitat of Yangtze finless porpoises overlaps extensively with gillnetting areas in the river, (Yu et al., 2005). Electric fishing also became common in the Yangtze River during the 1990s, and it probably kills porpoises outright and contributes to the depletion of their prey (Reeves et al. 2000) as well as entanglement in rolling hook long-lines. The porpoise population are also being affected indirectly due to the damage by mining of the river bed, lake beds and banks, much of it illegal. It is destroying important habitat of the porpoise’s prey, therefore affecting the porpoises. This problem is especially serious in Poyang Lake, (Xiao and Zhang, 2000; Wang et al., 2006). As their food source is short, porpoises are forced to increase their foraging area to hunt for fish in unknown regions. However this means coming into close dangerous contact with humans. In docking areas, there are a lot of remains discarded which attracts fish to go and feed there. Finless porpoises are willing to risk injury and even death to catch the fish.

 

The Yangtze finless porpoise is also under threat by nature. Due to global warming, the Yangtze River is experiencing more extreme weather conditions, causing the porpoise to find it more difficult to breed successfully and to survive. In February and March 2008, unexpected low temperatures caused the water in the Tian’ezhou reserve to freeze over. The porpoise broke the ice in desperation for air but also injured themselves on the sharp ice. Five finless porpoises, of which two were pregnant, were killed under the extreme conditions. In May 2011, a serious drought occurred in the middle and lower course of the Yangtze River. It was the worst in 50 years. Many lakes became grasslands with no fish during the finless porpoise’s breeding season, causing insufficient feeding

There have been some conservation efforts such as the establishment of five natural reserves along the middle and lower courses of the Yangtze River since 1986 for rare cetacean species, (Wang et al., 2006). However, there populations are still declining rapidly, (D. Wang et al., 2006; K. Wang et al., 2006b). The Chinese Government also 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). In the United States of America, the Marine Mammal Protection Act (MMPA) was amended to include the Yangtze finless porpoise.

This image shows the physical appearance of the now extinct Yangtze Baiji Dolphin.
Figure 5-The Yangtze Baiji Dolphin http://www.wildlifeextra.com/images/Baiji9medium.JPG

Better conservation and protection needs to be in place and enforced otherwise the Finless Porpoise shall suffer the same fate as the Baiji Dolphin, Lipotes vexillifer, (see fig. 5). Due to habitat loss caused by rapid development along the Yangtze River, its distribution was largely reduced and became limited to the main channel between Jingzhou and Jiangyin of 870 miles (Zhang et al., 2003). It’s population has also declined due to the threat of by-catch, pollution, vessel collision and underwater explosions from illegal fishing, which caused 19.4% of deaths in the lower course of the river between 1979 and 1981, (Zhou and Li, 1989). During November and December 2006, a multi-vessel visual and acoustic survey was conducted covering 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 is now extinct (Turvey et al., 2007). More similar surveys need to carried out to monitor the population size. However, it is difficult as the probability of detection is very low due to the porpoise only being small and finless making them harder to spot as they don’t break the water surface. They also have brief surfacing behaviour, (Akamatsu et al., 2002; Wei et al., 2002a; Zhang et al., 1996). Regulations need to be in place and enforced for boat traffic, pollution and fishing to be controlled so that the remaining Yangtze finless porpoise population can be maintained. However, the porpoises do not roam far (Zheng, 2005). This means that even if they were no longer threatened and had optimum habitat conditions, there is little chance that porpoises from other areas would repopulate the region, increasing the chance that finless porpoises will soon disappear permanently. However, if the environment was improved, the number of fish would increase, which would attract the porpoise. Efforts need to be taken to reduce the effect of human developments, pollution and fishing on the Yangtze Finless Porpoise population, their habitat and prey for the decline to cease. People need to become aware so that more research can be carried out to understand these animals better so that we can protect them successfully.

References

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Dong, W., Xu, Y., Wang, D., Hao, Y., (2006), Mercury concentrations in Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) from Eastern Dongting Lake, China, Fresenius Environmental Bulletin, 15,  441–447.

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Wei, Z., Zhang, X., Wang, K., Zhao, Q., Kuang, X., Wang, X., Wang, D., (2003), Habitat use and preliminary evaluation of the habitat status of the Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) in the Balijiang section of the Yangtze River, China, Acta Zoologica Sinica, 49, 163–170.

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Zhao, X., Barlow, J., Taylor, B. L., Pitman, R. L., Wang, K., Wei, Z., Wang, D., (2008), Abundance and conservation status of the Yangtze finless porpoise in the Yangtze River, China, Biological Conservation, 141(12), 3006-3018.

Zheng, J. S., Xia, J. H., He, S. P., Wang, D. (2005). Population genetic structure of the Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis): implications for management and conservation. Biochemical genetics, 43(5-6), 307-320.

Photo References

http://news.bbcimg.co.uk/media/images/65620000/jpg/_65620858_02.jpg

http://thewatchers.adorraeli.com/wp-content/uploads/2011/05/f04da2db14840f35eb7505.jpg http://www.wildlifeextra.com/images/Baiji9medium.JPG

http://www.discoveryangtze.com/Yangtzediscovery/photo/mapyangtze.jpg

http://www.theepochtimes.com/n2/images/stories/large/2010/09/02/103228017Yangtze.jpg

http://www.wildlifeextra.com/images/Baiji9medium.JPG

4 years ago

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