“‘Well, we might at least see a finless porpoise,’ he said.
‘They’re not as rare as the dolphins, are they?'”
Almost a quarter of a century after Douglas Adams alerted the world to the plight of the Yangtze’s critically endangered baiji, declared extinct just seven years ago, it appears Asia’s longest river is on the brink of losing its sole remaining cetacean. The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), a distinct subspecies of the narrow-ridged finless porpoise, is under threat from the same factors that led to the extinction of the baiji: extreme habitat degradation, fragmentation, and unacceptable levels of by-catch.
Several steps have been taken to promote the conservation of the porpoise, most notably the creation of seven nature reserves – including two ex-situ reserves designed to maintain reservoirs for replenishment of the river population – and the implementation of a 3-month annual fishing ban. Despite this, the population has been in continuous decline since the 1980s. The population is estimated to have plummeted from over 2500 in 1991 to less than 1300 in 2006. However, this worrying demographic trend is accelerating, with optimistic estimates predicting the extinction of the subspecies within the next century.
The prediction of looming extinction has this month received some ominous support, following the publication of the results from a 2012 census of the Yangtze finless porpoise population. The report estimates around 500 porpoises remain in the main stem of the river, suggesting a more than 50% population decline in just 6 years – compared to the 15 years taken for the population to halve from 1991-2006. This represents an order-of-magnitude increase in rate of decline in the past 20 years, far greater than any of the previous predictions of population decline.
At the current rate, it is likely this subspecies of porpoise will be extinct within the next 20 years, despite current conservation efforts (however limited). At the forefront of these efforts has been the creation of two ex-situ populations of porpoise in lakes connected to the river. It was hoped these populations would buffer the risk of rapid decline through steady immigration into the river. This buffer, however, seems to be also dwindling, with the two lake populations decreasing and gene flow into the river population from these populations appearing to have stagnated. This lack of connectivity is further compounded by increased shipping activity in the channel connecting one of the lakes to the river, effectively inhibiting migration.
It is clear that current efforts are insufficient to successfully conserve the Yangtze finless porpoise. Yet, in a region where biodiversity takes a back seat to economic priorities, it is unclear how much China is willing to invest – and sacrifice – to ensure the cetacean’s survival. The authors of the report recommend several measures that need to be taken to improve the porpoises chances of survival, including the revision and extension of the reserve network to promote connectivity, the creation of additional ex-situ reserves, and a whole-year fishing ban.
Given China’s track record on conservation issues in the Yangtze, it is unlikely these recommendations will be enforced with much gusto. Consequently, the Yangtze appears destined to lose both cetacean species within less than half a century, with its critically endangered alligator and sturgeon following closely behind.
Mei et al. 2014. The Yangtze finless porpoise: On an accelerating path to extinction? Biological Conservation 172:117-123.