Once again, human beings are responsible for the extinction of yet another wonderful creation from the face of this earth. This particular animal has been gradually disappearing from the Yangtze River since the end of the 20th century until it reached its extinction between 2005 and 2010.
The Chinese swordfish lived at the time when dinosaurs still existed before a mass extinction wiped them out. Its home was the Yangtze River where it fed on fish and crustaceans.
The swordfish population began to decline in the last century due to overfishing. To give you an idea of how things looked like before, in the 1970s an average of 25 tons of this large animal was caught each year.
However, the scientists of this study point to the construction of dams, mainly the one in Gezhouba, as the culprits in this animal's extinction. The Gezhouba dam was built in 1981 on the Yangtze, hindering the swordfish's journey to lay its eggs in the upper reaches of the river. This is why the fish could no longer reproduce.
Years passed and the number of swordfish continued to decline. Researchers cite 1993 as the year the animal became functionally extinct. This means that even if it does not disappear from the face of the earth, there are not enough individuals that can reproduce in a meaningful way. Despite this, specimens continued to be sighted and some were captured with the intention of breeding in captivity. Attempts have failed.
The last time a Chinese swordfish was seen was in 2003 when Qiwei Wei (the head researcher) and his team placed a tracking tag on a specimen caught accidentally near Yibin, in south-central China. The researchers released him to see where he was going, but within a few hours, his trail was lost.
Ivan Jaric is a biologist at the Czech Republic's Institute of Hydrobiology and the University of South Bohemia and co-author of the study. According to him, there may be some Chinese swordfish swimming around but it is very unlikely. "The lack of observations during the studies and over the past 16 years in rivers in highly urbanised regions with a considerable level of water use makes new observations unlikely," he says in the study.
The study published in Science of the Total Environment estimates that the fish became extinct sometime between 2005 and 2010. It also points out that efforts to conserve the animal should have been made before 1993 or at the latest by early 2000, which is when the situation began to escalate.
Chinese swordfish is related to American swordfish, which lives in the Mississippi River basin and is in a vulnerable situation. Both are related to the sturgeon family, 85% of which is currently endangered. According to the International Union for Conservation of Nature, it is the most threatened group of animals.
The importance of large fish is not only limited to their role within a given ecosystem, but they also act as guardians of environmental quality, as they can only live in healthy rivers.
Researchers are now focusing on the remaining species living in the Yangtze, because during the study they did not find any specimens of the 140 other species they expected to find in its waters. They urge early action to save those species for which there is still hope.
Source: Extinction of one of the world's largest freshwater fishes: Lessons for conserving the endangered Yangtze fauna. 2020 Science of The Total Environment. Hui Zhang, Ivan Jarić, David L. Roberts, Yongfeng He, Hao Du,Jinming Wu, Chengyou Wang,Qiwei Wei DOI: https://doi.org/10.1016/j.scitotenv.2019.136242