Provided by Professor Wang Ding on 8 December 2015
While ex situ conservation has been seen as an important strategy for endangered terrestrial animals, it is still controversial for cetaceans. The Critically Endangered Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is the only freshwater porpoise population in the world; it is restricted to the middle and lower reaches of China’s Yangtze River including two adjoining lakes. Due to habitat degradation and mortality from ship strikes and bycatch, the natural population of the subspecies has dramatically declined over the past several decades. According to the latest range-wide survey conducted in 2012, there were only approximately 1000 individuals left and the annual decline rate has been accelerating over the past decade.
In 1992, the Tian-E-Zhou Oxbow, an old natural channel in the middle reaches of the Yangtze, was chosen by the Chinese Government as a natural ex situ protection area for finless porpoises (as proposed by my Cetacean Research Group at the Institute of Hydrobiology, Chinese Academy of Sciences). Since this oxbow used to be connected to the river, its environment and ecological conditions are similar to those of the mainstem. Feasibility studies of the first introduced porpoises confirmed that they can not only survive but also reproduce successfully in the reserve. A census completed on 26th November 2015 revealed that the population had increased rapidly over the last five years. The population is now over 60, compared to only 25 in 2010. Excluding the eight animals introduced in 2014 and 2015, this population has shown a net growth of 108% with 27 new individuals over the past 5 years. Moreover, the population’s fecundity is considered high compared to the wild population. Of the 18 mature females at the Tian-E-Zhou oxbow, nine are pregnant (as diagnosed by ultrasound imaging) and 11 are lactating. Interestingly, of the 11 lactating females, four individuals are also pregnant. There are 17 juveniles younger than two years old, and of these, 11 were identified as newborns in 2015.
This natural ex situ population is regarded as an established Seed Population which we aim to release back into the subspecies’ natural habitat in the future when the Yangtze’s ecological conditions have improved and are more suitable for population recovery. According to previous work by our team, the capacity of the Tian-E-Zhou Oxbow to support finless porpoises, which is limited mainly by the fish resources in the oxbow, is 80 to 100 individuals. We estimate that the population could reach the local carrying capacity as early as 2018 if it keeps growing at the current rate. After 2018, some animals will have to be moved out periodically to regulate the oxbow population. In fact, four animals including 2 males and 2 females were already selected during the 2015 census to support a new natural ex situ population in He-Wang-Miao Oxbow, which is even bigger than the Tian-E-Zhou Oxbow with an estimated capacity for the finless porpoises of over 120 individuals. Our team believes that more ex situ populations will provide a firm basis for the Yangtze finless porpoise conservation project, and ultimately improve our chances to save this Critically Endangered freshwater subspecies.