Every year in June and July, when the Yangtze finless porpoise enters the peak birth season, people living in the Yangtze River basin also find that the summer rain begins to gradually increase. Especially this year, the middle and lower reaches of the Yangtze River basin have been affected by continuous heavy rainfall, and the water level has continued to rise, and there are even super-alert water levels in many places.
Heavy rainfall has brought many changes to people's lives and travel, and what will be the impact on the lives of the Yangtze finless porpoises living in the water?
Photographed by Zhang Kun
There are pros and cons: changes in the water ecological environment affect the survival of the Yangtze finless porpoise at all times
The Yangtze finless porpoise is an endemic freshwater cetacean that only lives in the Yangtze River on the mainland, and its calving, rearing, growth and reproduction processes are completed in the Yangtze River basin, so the hydrological conditions of the Yangtze River have an important impact on the distribution, migration and even survival of the finless porpoise in the Yangtze River.
In the past, human activities such as illegal fishing gear, shipping vessels, water conservancy projects, water pollution, and sand mining and flooding threatened the survival of the Yangtze finless porpoise, resulting in an accelerated decline in the Yangtze finless porpoise. The Yangtze River has always been the home of the Yangtze finless porpoise, and the changes in the water ecological environment of its basin have always affected the survival of the Yangtze finless porpoise.
In addition to human activities, extreme continuous heavy rainfall will also affect the Yangtze finless porpoise.
The World Wide Fund for Nature (WWF) pointed out in a popular science article that the impact of extreme rainstorms on the Yangtze finless porpoise is divided into two aspects. On a positive note, the continuous heavy rainfall in the Yangtze River basin has led to a rise in the water level of the Yangtze River and an expansion of the water area, providing a wider living space for the Yangtze finless porpoise and significantly reducing the conflict between human activities such as shipping and the finless porpoise. At the same time, with the increase of the water volume of the Yangtze River, more floodplain wetlands of the Yangtze River will be submerged, providing a broader place for the spawning and reproduction of a variety of fish and the development of juveniles, and providing more abundant bait resources for the finless porpoise in the current and next year.
However, it should not be ignored that the rainy season in the middle and lower reaches of the Yangtze River overlaps with the peak time when the Yangtze finless porpoise is born, and the heavy rainfall accelerates the river flow speed and the wind and waves are high, which can easily cause the separation of the newborn finless porpoise with the mother dolphin who is still weak in swimming ability, resulting in a decrease in the survival chance. At the same time, extremely heavy precipitation may inundate large areas of the terrestrial environment, and finless porpoises may also enter these areas with currents, such as some ditches and deep pits on the banks of the Yangtze River, as well as the embankments that have burst their banks. If the flood waters recede quickly, the finless porpoise is very likely to run aground without timely evacuation, resulting in injury or direct death. In addition, during floods, large amounts of floating debris or garbage can flow down the river, which can also pose a potential threat to finless porpoises.
Finless porpoise mother and child. Photo by Wu Jiamin
Extreme drought also poses a serious threat to the Yangtze finless porpoise
In recent years, extreme weather events caused by abnormal climate have occurred frequently, and the Yangtze River basin is particularly affected by extreme weather events. In addition to heavy rainfall, the Yangtze River basin is also experiencing dry weather with high temperatures and little rainfall. This is due to the influence of large-scale circulation factors and monsoons, and the Yangtze River basin is susceptible to the superposition of multiple disasters.
"Judging from the statistical results, the drought level in the Yangtze River basin has increased significantly." Cheng Hongguang, an expert of the overall group of the Yangtze River Ecological Environment Protection and Restoration Joint Research Center and dean of the Institute of Water Sciences of Beijing Normal University, pointed out in an exclusive interview with China Environment News: "Climate change profoundly affects the water cycle model and the spatial and temporal distribution of hydrological elements, causing changes in ecological and hydrological elements at different scales. ”
Statistics show that in 2006, 2011, 2013, 2019 and 2022, there were many times of compound high temperature and drought in the Yangtze River Basin. The amount of water required for ecosystem recovery after extreme drought is as high as 1.5-4 times the average precipitation, and the impact on ecosystems tends to last for a long time.
Compared with extreme heavy rainfall, climate events such as extreme drought and extreme low temperatures pose a more serious threat to the finless porpoise. Extreme drought has reduced precipitation, lowered water levels and reduced water areas in the Yangtze River, posing a serious threat to the Yangtze finless porpoise, especially in Poyang and Dongting lakes.
The WWF pointed out in an article that extreme drought has reduced the water flow from the upper tributaries of the lake, coupled with the combined effect of the decline in the water level of the main stream of the Yangtze River, the lake area will shrink rapidly, forcing the finless porpoise in the lake area to concentrate in the main channel waters, further exacerbating the contradiction between human activities such as shipping and sand dredging and the survival of the finless porpoise.
According to the analysis of the data collected by relevant agencies over the years, there is a clear correlation between the number of stranded and dead finless porpoises and the change of the water level of the Yangtze River: most of the finless porpoise deaths and stranding events occur during the dry season, especially in the years and seasons of extreme drought, taking 2022 as an example, the middle and lower reaches of the Yangtze River have experienced continuous extreme drought weather, the water area of Poyang Lake has shrunk, and a large number of finless porpoises have been trapped in large sand pits (butterfly lakes) formed by sand dredging.
Nowadays, extreme weather not only affects the survival of human beings, but also poses an increasingly serious real threat to cetaceans such as the Yangtze finless porpoise, and how to deal with global climate change and effectively mitigate the impact of climate change on cetaceans has become an urgent problem to be solved.
In this regard, WWF proposes to formulate early warning and prevention measures for extreme climate events, and establish a global cetacean monitoring and early warning mechanism based on the analysis of global climate change trends and the distribution and ecological characteristics of global cetaceans, so as to provide macro strategic guidance for cetacean conservation. Cetaceans should be used as sentinel species in global climate change monitoring and research, and a global coordination mechanism should be established to establish assessment standards for the impact of climate change on cetaceans, so as to provide support for research on countermeasures to global climate change. For species that are susceptible to extreme weather, research and formulate emergency rescue mechanisms, establish emergency rescue teams, and improve the success rate of rescue.