Scientific facts on the Yangtze river porpoise

When I tell other people about the Yangtze finless porpoise, their first reaction is nearly always: “But how does it swim?” I'm sure they're picturing something that resembles a dolphin just rolling and floating around in the water, because they are also usually laughing when they try to picture it. In fact, the Yangtze river dolphin lacks a dorsal fin, yes, but it still has everything else in place that it needs to swim. Some researchers suggest that the lack of a dorsal fin is an adaptation to their environment. It might have something to do with the relatively calmer, shallower waters that they inhabit as compared with their sea-dwelling relatives.

The Yangtze finless porpoise is actually a sub-species of finless porpoises. The other populations are found along the coasts of Japan and China. There is also a similar species that is attempting to survive in the upper reaches of the Ganges River. The freshwater sub-species survive by means similar to other porpoises and dolphins. They use echolocation to navigate underwater and feed on fish. They also live in pods or small groups and communicate with each other through clicks and squeaks. Studies on their communication habits suggest that, perhaps because of the higher sediment load of the Yangtze River, these porpoises produce clicks at higher frequencies than saltwater porpoises.

A number of population studies have been carried out over the past few decades, and none of the trends are good. One carefully conducted population survey of Yangtze finless porpoises was conducted using two boats and field observations from the upper Yangtze River by Yichang down to the lower Yangtze River by Shanghai in November and December 2006.

Zhao, W., Barlow, J., Taylor, B. L., Pitman, R. L., Wang, K., Wei, Z., Stewart, B., Turvey, S.T., Akamatsu, T., Reeves, R.R., Wang, D. (2008). Abundance and conservation status of the Yangtze finless porpoise in the Yangtze River, China. Biological Conservation, 141:3008-3018.

The greatest amount of porpoises were found in the middle reaches of the river, around Wuhan and down to Poyang Lake. The smallest, and also most separated, population was at the upper reaches by Yichang. Both Dongting Lake and Poyang Lake existed as important habitats for this animal in the past, but now the porpoises face severe threats in these places as well as throughout the rest of their range. Depending on the statistical measures used, estimates of the porpoises from older studies (late 1980s to early 1990s) tell us that populations went from between 1450 and 1650 individuals down to about 800 individuals in 2006. (These are the numbers I kept reading that made me stop and want to just hide my head under a blanket instead of continuing with the blog.)

At the Baiji Dolphinarium in Wuhan, captive breeding programs have been carried out successfully. Judging from their publications, the authors from this research station do not appear confident in the porpoise's survival prospects in its natural environment and they stress the need for more captive breeding in order to understand the reproductive behaviors of the animal. The females can breed at around six years of age. The first freshwater finless porpoise born in captivity was a male at the Baiji Dolphinarium in 2005. These researchers also stress the the need for more and better reserves. So far, the most successful and encouraging reserve is the Tian'e-Zhou Oxbow Nature Reserve, formed by the Yangtze River near Shishou and now serving as the protected home of at least thirty porpoises that have been allowed to live and breed there.

As I mentioned briefly in my previous post, the Yangtze river porpoise's protection status has been upgraded. In my next post I will discuss what this means along with what it means in terms of conservation protocol.