The recent decline in baiji abundance has been attributed to excessive bycatch in fisheries, reduced abundance of prey due to overfishing, and severe degradation of the Yangtze environment. A second cetacean species shares the Yangtze River system with the baiji. Yangtze finless porpoises are considered a subspecies, and they appear to be morphologically, behaviorally, and genetically different from the marine finless porpoises that occur in Chinese coastal waters and elsewhere in eastern and southern Asia. Although population estimates are crude, there are thought to be at least hundreds, and perhaps a few thousand, finless porpoises remaining in the Yangtze system, including Dongting and Poyang lakes. While the finless porpoise seems to have been better able than the baiji to tolerate the deteriorating conditions in the Yangtze River over the last several decades, its future is highly uncertain.
Dolphins inhabit several large rivers of southern Asia.
These are obligate river dolphins that occurred historically from the deltaic zones upriver to the mountain foothills where rapids blocked their dispersal. These populations are subject to many of the same threats and are in urgent need of assessment and protection. The Ganges susu occurs in the inland waters of Bangladesh, India, and Nepal. Its traditional strongholds have been the Ganges, Brahmaputra, Meghna, and Karnaphuli river systems. Susus still occur in these rivers and, at least seasonally, in many of their tributaries.