From 1800, 1045, 1012, to more than 1200, the Ministry of Agriculture and Rural Affairs announced on the 28th that the latest population of finless porpoises surveyed was 1249, which is the first time since the first scientific expedition of the Yangtze finless porpoise in 2006, the core data of "giant pandas in the water" stopped falling and rebounded, achieving a historic turning point.
It can be said that in the second year of the full implementation of the ten-year fishing ban on the Yangtze River, the "smiling angel" in the mother river successfully walked out of a "smile curve". Compared to the previous survey, their number increased by 23.42% in 5 years, with an average annual growth rate of 4.3%. A reporter from Jiefang Daily Shangguan News interviewed experts who participated in the scientific expedition of the Yangtze River porpoise.
[Eat fierce big birds, but also eat delicious knives]
Li Jianhua, a member of the Strategic Research Center for Ecological Conservation of Yangtze River Waters and a teacher at Shanghai Ocean University, witnessed a whole group of finless porpoises in groups of eight or nine in Poyang Lake, and the most excited and happiest thing was to see the mother and child escort, the mother of the dolphin with a baby dolphin of more than 1 meter.
In Li Jianhua's eyes, finless porpoises are very intelligent aquatic creatures. They eat only live fish, and can eat fierce anchovy, as well as delicious knifefish. This survey shows that the distribution area of some species has expanded significantly, in addition to the Yangtze finless porpoise's range has increased significantly, the number of swordfish - "knife fish" in the Yangtze River has also increased significantly, and can anadromous migration to the farthest water in history, Dongting Lake.
Interestingly, finless porpoises have their own "language" communication capabilities, emitting high-frequency signals that are inaudible to the human ear, which is the only special feature that freshwater dolphins have. Compared with other endangered or even recently extinct aquatic organisms of the Yangtze River, they are better at "seeking benefits and avoiding harm", "choosing water to live", and choosing the most suitable environment for living in rivers and lakes.
[By sight, sonar, AI, DNA recognition]
On the great rivers, what means does the census rely on? In 2019, Mr. Li Jianhua was selected by the school to take up the post of "Yangtze River Office", starting from project demonstration and design, and participated in the 4th "Population Census" of the finless porpoise industry every 5 years. She said that the "census" not only relies on visual and sonar information, but also applies a number of new technologies. For example, video-based artificial intelligence (AI) recognition, which collects images throughout the boat, uses AI "dolphin" face recognition, and accurately "names and reports".
Another example is environmental DNA analysis, which can not only find clues left by finless porpoises, but also find out whether there is a familial relationship between relevant genetic evidence. Li Chenhong, director of the Environmental DNA Technology and Aquatic Ecological Health Assessment Engineering Center at Shanghai Ocean University, explained that any organism that survives in a water body will "excrete" some DNA, "Take out 1 liter of lake water, and there may be DNA emitted by the body fluids or scales of fish." "Therefore, the DNA can be extracted, analyzed, and databases and monitoring networks can be established." This method is less labor-intensive and efficient than the original aquatic biological survey and research, and can be measured even when the concentration of DNA in water is very low. ”
[After the fishing ban, there will be fish every year, and the one-way street will give up the right of way]
So, what is the trend of the finless porpoise in the later stage? It should be said that the finless porpoise population is still only in the recovery period. During the scientific expedition of the Yangtze finless porpoise in the whole basin, about 595 finless porpoises in the main stream of the Yangtze River, about 492 in Poyang Lake and about 162 in Dongting Lake. Between the main stream of the Yangtze River from Nanjing to Shanghai, Li Jianhua and their sailed for more than ten days, only looking at a few finless porpoises, and they felt like "finding a needle in a haystack".
Fortunately, fishing in the Yangtze River has been banned for ten years, and there are no nets or fishing boats on the river, creating a living circle for finless porpoises that "fish every year". The survey shows that 193 species of fish were monitored in key waters of the Yangtze River Basin in 2022, an increase of 25 species from 168 in 2020. Li Jianhua said that sometimes silver carp in the river will accidentally jump on the boat, so porpoise food is still abundant. At the same time, in order to minimize the impact of golden waterway shipping, porpoise-infested waters set up a one-way traffic mode, ceding half of the "right of way" to them. With finless porpoise as a landmark species, the aquatic biodiversity of the Yangtze River is gradually recovering, and aquatic biological resources are showing a trend of recovery.
图片来源：受访者提供 Source: Author: Xu Ruizhe