Large animals (“megafauna”) around the world are under pressure from human activities, and many well-known species are threatened with extinction. Of all the megafauna, species that live in freshwater are particularly threatened. For these animals, human-produced changes are intense and protected areas are lacking. For example, all freshwater cetaceans (aquatic mammals) in the world are endangered. They often live in a single large river basin and, thus, naturally have very restricted ranges, making them especially vulnerable.
China’s longest river, the Yahtzee, is one of the busiest shipping routes in the world and has been a main thoroughfare for Chinese commerce for thousands of years. But shipping traffic poses great pressures on aquatic megafauna in terms of collisions and disturbance of habitat, including noise pollution, which is particularly threatening to cetaceans that use echolocation. One freshwater cetacean, the Yahtzee River Dolphin (Lipotes vexillifer) is already extinct. New research is now focused on the remaining species, the Yangtze Finless Porpoise (Neophocoena asiaorientalis).
Mei et al., 2021, investigated the distributional overlap of porpoises and cargo ships in a busy 650 km section of Yangtze River, comparing data from 2017 with 2012 and 2006 data. Using boat-based surveys, they measured the distance of porpoises from river banks and sand bars, and also determined the positions of boats with satellite imagery. The researchers found that the areas within 300 metres of river banks are important habitats for porpoises and accounted for 54 percent of sighting records. However, this same area close to the banks overlapped with where 62 percent of ships travelled upstream, in order to avoid the strong current. Moreover, the percentage of porpoises observed within this preferred area significantly decreased from 2006 to 2017, suggesting that the porpoises are changing their habitat selection due to the shipping activity.
The authors found that shipping increased 65 percent from 2006–2017, which indicates the urgent need to conserve the porpoise. The authors recommend restricting vessels to travel within designated channels that are less preferred by porpoises, and protecting areas that are frequently used by porpoise near sandbars. The authors also call for similar research on other megafauna living in the great rivers of the world, as the amount of shipping is expected to further increase throughout the next century.
Mei, Z., Y. Han, S. T. Turvey, J. Liu, Z. Wang, G. Nabi, M. Chen et al. 2021. Mitigating the effect of shipping on freshwater cetaceans: The case study of the Yangtze finless porpoise. Biological Conservation 257: 109132.
Photographs by Wei Ye(韦晔).
This RIT is part of a series: ‘Letters from China’, which periodically summarizes new research from ecology and conservation from China. It is curated by Dr. Eben Goodale, Professor at the College of Forestry, Guangxi University, China, with editorial support from Dr. Krishnapriya Tamma, Assistant Professor, Azim Premji University, India. Click on the ‘Letters from China’ tag above the article title to read other RITs in this series.