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Why did the Yangtze River white sturgeon become extinct? Experts: Dams affect spawning, from flourishing to extinction in just over 20 years

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Why did the Yangtze River white sturgeon become extinct? Experts: Dams affect spawning, from flourishing to extinction in just over 20 years

At the Museum of the Wuhan Institute of Aquatic Sciences, a specimen of the white sturgeon lies quietly, telling the story of how it once survived. (Photo: Di LiHui)

Guide

The IUCN's Red List of Threatened Species, updated on July 21, 2022 Beijing time, shows that the Yangtze River white sturgeon (Psephurus gladius) has become extinct. In fact, as early as 2019, 8 researchers from China, the Czech Republic and the United Kingdom announced the extinction of the Yangtze River white sturgeon. As for the cause of the extinction, researchers believe it is related to the dam on the Yangtze River.

Written by | Xia Zhijian

Editor| Di Li Hui

On January 24, 2003, a 3.52-meter-long female white sturgeon weighing about 160 kilograms and about 20 years old was mistakenly caught by a fisherman in Nanxi County, Yibin, Sichuan Province. After being rescued, after three days of treatment, it was released into the Yangtze River on January 27. This is the last human encounter with the white sturgeon in the credible record, and this white sturgeon is likely to be the last in the white sturgeon family.

At the end of 2019, eight researchers from China, the Czech Republic and the United Kingdom finally declared the extinction of the Yangtze River white sturgeon. As for the cause of the extinction, researchers believe it is related to the dam on the Yangtze River.

39 years ago, gezhouba, the first dam across the Yangtze River, intercepted helong.

As a migratory fish, in the long history of time, the white sturgeon will migrate to the Yibin-Chongqing section of the upper reaches of the Yangtze River every spring to spawn. The completion of gezhou dam has blocked the Yangtze River waterway that the white sturgeon has traveled countless times, and also ended their fate of continuing to thrive on this planet.

In the decades after the dam Helong, this water fish king, who has been riding the Yangtze River for hundreds of millions of years, has embarked on the road to extinction because of the dam's obstruction, coupled with habitat fragmentation and human overfishing.

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On December 23, 2019, Science of the Total Environment published a paper online titled "The Extinction of One of the World's Largest Freshwater Fish: Lessons from Protecting Endangered Fauna in the Yangtze River."

The International Union for Conservation of Nature (IUCN) assessed the living conditions of white sturgeon in 2009, when it was classified as "critically endangered" [2]. In the latest paper on white sturgeon, the researchers write: "Based on extensive surveys and statistical evaluations of observational records, we found that white sturgeon may have become extinct prior to the most recent 2009 IUCN Red List assessment." Currently, not a single surviving individual of white sturgeon has been captured, and no living tissue has been preserved to provide the possibility of reviving the species. ”

Wei Qiwei, a researcher at the Yangtze River Fisheries Research Institute of the Chinese Academy of Fishery Sciences and an expert on sturgeon research, is the first responsible author of the paper, and this assertion is based on a comprehensive fish resource survey he and his colleagues did in the Yangtze River Basin from 2017 to 2018, including the use of fishing nets, cages and other methods to conduct 10 hours of active sampling per quarter when weather conditions permit, as well as to investigate the passive sampling of traditional fish market catches in major towns along the Yangtze River.

A total of 332 species of fish were found in that comprehensive survey, 39 of which had not been previously found in the Yangtze River Basin. Worryingly, 140 species of fish previously documented in the Yangtze River basin were not found in the survey, and the vast majority of them are highly endangered species, including the white sturgeon.

Using the sampling data from this survey, combined with historically credible white sturgeon observation records (210 white sturgeon were observed from 1981 to 2003), after statistical analysis, the researchers found that the white sturgeon had become extinct in 2003 (no later than 2010), and the white sturgeon living in the upper reaches of Gezhouba had become functionally extinct in 1993. When the last individual of a species dies, the species is declared "extinct"; Functional extinction, on the other hand, means that there are no more individuals in the remaining population that can reproduce, or that due to the scarcity of the population, unavoidable inbreeding and genetic drift will make the survival of the population difficult to maintain.

Just as cancer patients cannot escape the fate of death after entering the advanced stage of cancer, once a species enters the stage of functional extinction, it will eventually escape the fate of extinction.

The white sturgeon, from prosperity to extinction, but it took more than twenty years.

In the 1970s, fishermen living along the Yangtze River could catch up to 25 tons of white sturgeon a year; According to historical records, in earlier times, in addition to the Yangtze River, white sturgeon was also distributed in the lower reaches and estuaries of the Yellow River, Qiantang River, Yongjiang River and other rivers [4].

The proverb passed down by Sichuan fishermen tells the story of the Yangtze River that once rolled over chinese sturgeon, rouge fish, white sturgeon and other big fish, and the proverbial "10,000 jin elephant" is a white sturgeon with a long nose.

The barrier of Gezhouba allowed the white sturgeon to survive the Cretaceous mass extinction and several glacial and interglacial periods in the Quaternary Period, and could not return to the upper reaches of the Yangtze River to breed new life. Unlike many other migratory fish species that have spawning grounds downstream of Gezhouba, the white sturgeon has been found to have spawning grounds only in the upper reaches of the Yangtze River.

"Broodstock caught under the dam decreased year by year from 1985 to 1990, in order of 21, 8, 10, 6, 6 and 2, and no catch after 1991. The number of juvenile white sturgeon caught in Chongming, Shanghai from 1983 to 1988 also declined in fluctuations, with 587, 9, 84, 2 and 5 tails, and no more after 1989. Chang Jianbo and others of the Institute of Hydrobiology of the Chinese Academy of Sciences wrote in 1998 in "The Controversy and Enlightenment of the Fish Rescue Problem of the Gezhouba Project".

Wei Qiwei believes that the completion of the Gezhou Dam in 1981 is the most important factor in promoting the extinction of the white sturgeon, which artificially divides the white sturgeon into two populations, blocking the migration channel, and the white sturgeon that cannot return to the upstream to lay eggs has lost the ability to reproduce.

However, the breeding dilemma caused by the Gezhou Dam barrier is not the only factor that causes the bad luck of the white sturgeon, and the indiscriminate fishing is also an important reason for the white sturgeon to push the white sturgeon step by step into the abyss of destruction.

Yu Zhitang and others from the Institute of Hydrobiology of the Chinese Academy of Sciences wrote in a paper published in the Journal of Hydrobiology in September 1986 [4]

"In the 'Circular Order on the Strict Protection of Rare and Rare Wild Animals' issued by the State Council on April 13, 1983, the white sturgeon was listed as one of the protected objects. However, in addition to the ban on the fishing of white sturgeon in Sichuan Province and Yichang District Fishery Administration Station, the resources of white sturgeon are still not strictly protected and managed in various parts of the Yangtze River, so that in 1983, fishermen along the Yangtze River caught a large number of juvenile white sturgeon fish, which greatly damaged the resources; To this day, the phenomenon of hunting white sturgeon in various places still occurs from time to time. ”

This seems to be confirmed in the latest paper.

Why did the Yangtze River white sturgeon become extinct? Experts: Dams affect spawning, from flourishing to extinction in just over 20 years

1981-2002 White sturgeon catch downstream of Gezhouba, courtesy of Wei Qiwei and Zhang Hui

From the above figure cited in the paper, it is clear that the amount of white sturgeon in the lower reaches of Gezhouba experienced a rapid increase in 1983-1985, and after 1985, it fell off a cliff.

Wei Qiwei told Mr. Sai: "Judging from the data on the misattaught of white sturgeon under Gezhouba from 1981 to 1993, the natural reproduction of upstream white sturgeon has been gradually hindered. Fishing has accelerated the breeding and disappearance of the upstream white sturgeon. We believe that the Gezhou Dam barrier is a more important factor affecting the extinction of white sturgeon species. ”

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Fish in the Family Polyodontidae are often referred to as "primitive fish", and the fossil record shows that they appeared on Earth 70-75 million years ago, in the same era as dinosaurs. The known spoon-sturgeon family consists of 6 genera, of which 4 have left only fossils, leaving two, one is the probably extinct white sturgeon and the other is the spoon-sturgeon that still roams in the Mississippi River Basin.

Why did the Yangtze River white sturgeon become extinct? Experts: Dams affect spawning, from flourishing to extinction in just over 20 years

Spoon sturgeon (Source: Wikipedia)

To some extent, after the emergence of the human species, the white sturgeon and the spoon sturgeon had a very similar tragic experience.

In the United States, which industrialized earlier than China, the Mississippi River also had a high tide of damming in the last century — 27 dams were built on the Mississippi River alone from Minneapolis to St. Louis. Like the white sturgeon, spoon-sturgeon are migratory fish that travel long distances up the river each year before spawning. After the Damming of the Mississippi River, the number of spoon sturgeon declined unsurprisingly.

Overfishing has also led to a cliff-like decline in spoon sturgeon catches. From 1958 to 1960, the catch of spoon sturgeon in the Norris Reservoir on the Clinch River in northeastern Tennessee dropped rapidly from 781 (20,275 kg) to 233 (5,690 kg) and 63 (1,070 kg) in three years.

Damming, overfishing, environmental pollution and channelization of rivers have all suffered from the problems that spoon sturgeon has encountered, and as a result, spoon sturgeon, which was widely distributed in the central and northern regions of the United States before 1900 and in the nearby Gulf coastal strip, has been extinct in Maryland, New York, North Carolina and Pennsylvania, as well as throughout Canada, and is currently distributed in only 22 states in the United States.

Despite this, spoon-sturgeon eventually survived, and populations returned to the point where commercial fishing was allowed in 11 U.S. states.

In addition to the conservation of spoon sturgeon by means of controlled fishing, habitat protection, artificial stocking and other measures, the United States also conducted experimental studies on the artificial breeding and juvenile breeding of spoon sturgeon in the early 1960s, and achieved success, and maintained the commercial and sport fishing fisheries of spoon sturgeon in some areas through artificial breeding.

China also had the opportunity to save the Yangtze River white sturgeon by intensifying research on artificial breeding.

In the 1980s, when many experts were discussing the impact of the construction of Gezhou Dam on the fish resources of the Yangtze River, many scholars, including Yu Zhitang, proposed that artificial breeding should be one of the important measures to conserve white sturgeon, and researchers at that time found mature white sturgeon individuals in the lower reaches of Gezhouba, which meant that artificial breeding of white sturgeon was likely to be successful [4].

However, at that time, the resources and energy of domestic protection of Yangtze River fish species were mainly invested in the more concerned Chinese sturgeon - in February 1982, at the debate meeting on the fish rescue issue of the Gezhouba Project held by the then State Agricultural Commission, the participating experts unanimously agreed to only use the Chinese sturgeon as the object of fish rescue [7].

"The country's economic level, technical level and concept at that time were not like now, and it could only take into account the Chinese sturgeon that was considered to be the most important first, and there was no key investment in the white sturgeon country." Wei Qiwei said.

Lack of attention and insufficient research has missed the last opportunity to save and study the white sturgeon in detail, and even to this day we cannot even know exactly the range of life of this species, although there are records of the white sturgeon in the Book of Poetry and the Book of Rites more than 2,000 years ago. In the paper by Wei Qiwei et al., they only estimated the lifespan of white sturgeon to be 29-38 years from the existing records of sexual maturity of female white sturgeon and the natural mortality rate data of white sturgeon.

Why did two big fish that are related to each other end up with such different fates in China and the United States?

"Although the spoon sturgeon in the Mississippi River Basin in the United States is also significantly affected by the dam, it has not finally become extinct, one is that the species is more widely distributed, and many tributaries have spawning grounds, while the Chinese white sturgeon spawning population is only found in the Yibin area, which is more demanding; Second, the protection and restoration efforts invested by the United States are much greater; The third is that the waters where the American spoon sturgeon are distributed is less stressful than that of the Yangtze River. Wei Qiwei concluded.

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Is the white sturgeon really extinct? There may be a glimmer of "hope".

The methods used to survey white sturgeon included active sampling through tools such as fishing nets and passive sampling by visits to fish markets, both of which may actually be missing. For example, when researchers sampled from point A to point B, it is possible that the white sturgeon has swam from point B to point A or point C; Moreover, due to the large amount of fishing that humans have previously fished, the white sturgeon may have developed adaptive behavior, deliberately avoiding human activities and living in more inaccessible places, which makes the discovery of the white sturgeon more difficult.

In response to the interview email of "Mr. Sai", Zhang Hui, one of the authors of the paper, made some explanations on the sampling method: "The first phase of the Yangtze River Fishery Resources and Environment Survey is 2017-2021, lasting 5 years, with an annual investment of about 10 million yuan, and more than 20 units have participated. Due to the vast scope of the Yangtze River Basin and the limitations of people and property, the problem of sampling omissions cannot be completely ruled out. ”

Zhang Hui also said that there is also a possibility that species declared extinct will be rediscovered many years later (such as ivory-beaked woodpeckers), but based on the results of existing field investigations and model theory analysis, it is determined that there is no problem with the extinction of white sturgeon.

Although the white sturgeon may still have the possibility of surviving individuals in the world, these possible remnants are reflected in the fact that they face a far more difficult survival situation than they did 17 years ago. As a species at the top of the food chain in the Yangtze River Basin, the depleted fish resources of the Yangtze River may have been difficult to support the survival of the white sturgeon.

Years of intense overfishing have led to a significant shrinkage in the resources of the "four major fishes" (blue carp, grass carp, silver carp and bighead carp) in the Yangtze River Basin compared with the 1950s – the incidence of seedlings has decreased by 93.5%, and the number of eggs produced has decreased from 120 billion per year to 1 billion per year.

Moreover, in the absence of effective management, the decline in fishery resources has led to a worsening of overfishing. In order to catch as many fish as possible in the Yangtze River, where there are fewer and fewer fish, fishermen have long been catching fish in extreme ways such as power grids, "ecstasy arrays" and "desperate nets", and as a result, after the end of the four-month spring fishing ban period in the Yangtze River, many young fish that have just hatched have not yet grown up and are fished out.

The Yangtze River is cursed and falls into a vicious circle of "the fishery resources are less and less, and the fishermen are getting poorer and poorer.".

As early as 2006, during the "two sessions", Cao Wenxuan, an academician of the Chinese Academy of Sciences, called for a ten-year ban on fishing in the Yangtze River to allow all kinds of fish stocks in the Yangtze River to have enough time to restore their populations. In ten years, the average fish can reproduce for 2-3 generations, so that the population of the fish population can be fundamentally increased, and the flagship species that feed on fish, such as finless porpoises and white sturgeon (if there are still living individuals), have the hope of surviving. In the field of ecology, there is the concept of "minimum surviving population", that is, the minimum effective amount needed to ensure that the population can survive healthily for a certain period of time, which is a threshold for the number of populations, and below this threshold, the population will gradually become extinct.

On December 15, 1960, after three years of cliff-like declines in white sturgeon catches, norris Reservoir in Tennessee, USA, began to ban commercial fishing in order to restore spoon sturgeon stocks. After 20 years, the sturgeon population in the reservoir was finally restored.

In January 2019, 14 years after Cao Wenxuan's appeal, the Chinese government finally made up its mind to achieve a total fishing ban in the Yangtze River Basin by the end of 2020, tentatively setting a 10-year fishing ban. The hundreds of species of fish still living in the Yangtze River have finally waited for this long-overdue respite.

It's just that for the white sturgeon, it's all too late.

Resources

[1]https://www.sciencedirect.com/science/article/pii/S0048969719362382

[2]https://www.iucnredlist.org/species/18428/8264989

[3] http://www.xinhuanet.com/local/2020-01/07/c_1125428621.htm

Yu Zhitang,Deng Zhonglin,Zhao Yan,Huang Xuan. Preliminary observations on the development of white sturgeon gonads downstream of Gezhouba junction[J].Chinese Journal of Hydrobiology,1986(03):295-296.

[5] https://en.wikipedia.org/wiki/Paddlefish

Liu Jiashou,Yu Zhitang. Spoon sturgeon and its fisheries in the United States[J].Chinese Journal of Hydrobiology,1990(01):75-83.

Chang Jianbo et al. Controversy and enlightenment of the fish rescue problem of Gezhouba Project. See: Ecology and Environmental Protection in Large-scale Water Conservancy Projects of the Yangtze River in the 21st Century. Beijing: China Environmental Science Press,1998.]

Li Chuxin,Zhu Yaohu. The Yangtze River Basin will be completely banned from fishing for 10 years[J].Ecological Economy,2019,35(12):9-12.

[9] Minimum survival population (MVP)——A basic theory of conservation biology[J].Chinese Journal of Ecology, 1996(02):26-31.