Dams and Fish

Yangtze fish take a hit

(July 19, 2011) China’s weekly newspaper, the Economic Observer, says the Three Gorges dam is the primary reason for the demise of the Yangtze’s “big four” fish species. By changing the hydrological regime downstream of the dam, the fry population of the black, grass, silver, and bighead carp have plummeted by 97%. Attempts to simulate the original hydrological conditions with forced water releases and restocking the river with broodstock will be futile say experts.  The damage is “irreversible” says Zhao Yimin, director of the Office of the Yangtze River Fishery Resources Committee in the Ministry of Agriculture. Artificial measures, he says will only slow down the inevitable decline in the fish stocks.

The Economic Observer delivers on its promise to provide “in-depth and independent” news and analysis with this piece. Read Probe International’s translation of the original.

Fish fry population declines by 97%, Three Gorges forced to release more water to simulate natural flooding

by Tian Peng

Originally published in the Economic Observer (Jingji guancha bao) on June 23, 2011

Translation by Probe International

On June 16, 2011, the Yangtze Flood Control and Drought Relief Headquarters under the Ministry of Water Resources issued a notice requiring that the Three Gorges Group Corporation immediately release more water from the reservoir for six days. The noticed called for an increase of an additional 2,000 cubic meters per second. The purpose was to simulate the natural flood peaks below the dam that the “four big-named cultivated fish” – or “big four” for short – have adapted to and to somehow address the alarming problem of the sharp decline in the fry population.

The “big four” — black carp, grass carp, silver carp and bighead carp — are not only the dominant species of freshwater aquaculture in China, they are the top catch of all freshwater fish in the country. While all fish stocks in the Yangtze have been in decline, the “big four” have been in sharp decline due to intensive shipping, destructive dredging, urban sprawl along the river, and especially the filling of the Three Gorges reservoir.

According to Three Gorges Project Ecology and Environmental Monitoring Bulletin 2010:

“The fry population of the ‘big four’ was 42 million in the Jianli section (of the Yangtze) below the dam in the period from May to July of 2009, 76.9% less than the same period of time last year and only 1.7% of the average in the same time period before the Three Gorges reservoir was filled (from 1997-2002). The spawning that would normally have taken place did not seem to be happening and the fry population of the ‘big four’ remained at a relatively low level.”

According to Zhao Yimin, director of the Office of the Yangtze River Fishery Resources Committee in the Ministry of Agriculture, the Three Gorges dam has not only dramatically shrunk the spawning grounds for the “big four,” it has also changed the water conditions below the dam, leading to a decline in the “big four” fry population by 97%.

Earlier in April this year, a considerable number of broodstock (or brood fish)[i] of the “big four” were released into the Yangtze River in an attempt to increase their population. However, this attempt to reverse the decline of the “big four” is far from guaranteed because the broodstock requires special water conditions to lay eggs: the water must be the right temperature, with the right flow and volume, and at the right time.

Take the black carp, for example. In order to lay its eggs, the black carp requires water at 18 and 21 degrees Celsius and with a hydrodynamic flow of 1 to 3 meters per second so that it swirls to create a special level of aeration. Finally, these conditions must continue for at least 5 days.

Chen Jin, Vice President of the Wuhan-based Yangtze River Scientific Research Institute (under the Changjiang Water Resources Commission), concluded there are four reasons for the sharp decline in the fry population: first, the construction of hydro dams and other water projects such as sluices; second, the construction of dykes that turned lakes into dry land and separated the river from the lakes thereby interrupting the spawning and growth cycle of the “big four” which lay their eggs in the Yangtze River but mature in lakes; third, over-fishing; fourth, water pollution.

According to Zhao Yimin, releasing more broodstock into the river and simulating flood peaks is an experiment that will likely fail to restore the population of the “big four” to levels that existed before the Three Gorges reservoir was filled.

“There the dam stands, having changed the river habitat in a massive way from what the ‘big four’ were used to. One of the most important issues is the disappearance of the spawning grounds below the dam. Objectively speaking, the current situation is irreversible – we can merely try to stabilize the situation. To be honest, artificial measures can only slow the trend of the declining population. If no measures are taken, this decline will continue at a much more rapid pace, eventually rendering the ‘big four’ species extinct.”

Chen Jin agreed that it is difficult to restore the previous situation for the “big four.”

“(Recovery) is only a dream. Even if the fry population reaches 200 to 300 million each year, no one is able to change those bad, old practices[ii] at one stroke. It’s also impossible to improve the situation through one-time measures. Various sectors, such as fisheries, water resources, and the power sector should work together to improve the fish population slowly and steadily. Individuals living along the river should also be involved.”

Zhao Yimin stressed that “the grand scheme to develop hydropower” has had a devastating impact on the aquatic life of the Yangtze River.

“The issue is not only that the Three Gorges dam is now built, but twenty and even thirty more hydropower stations are being constructed or are planned for the upstream main channel of the Yangtze. Xiangjiaba and Xiluodu for instance are scheduled to begin generating power next year and, the environmental destruction will increase in severity as more dams are built, one by one, upstream of Three Gorges. Here we are only talking about the ‘big four’. But there are one hundred and forty or fifty rare fish species in the Yangtze River, most of which are living in the upper reaches. Many of the rare fish have very specific survival conditions; so building even one dam will wipe them out. We use the ‘big four’ as an example but, in fact, some fish species are even more seriously threatened than the ‘big four,’ and are on the brink of extinction.”

According to Chen Jin, “In the upper reaches of the Yangtze, hydro dams are everywhere, on all the tributaries. The only exception is the Chishui River. Not only is the river a drinking water source,[iii] but more importantly, it is the location of the Maotai Wine Factory so no hydro station can be built there.”[iv]

Zhao Yimin appeared pessimistic about the protection of aquatic life in the Yangtze River. He believes that if the expansion of hydro power stations on the main channel of the Yangtze is unstoppable, at least several “complete tributaries” should be left untouched.

“But in reality,” he laments, “this goal is impossible because hydro dams are being built on all the major tributaries in the upper Yangtze, except the Chishui River. We cannot see a way to accomplish both protection and development.”

[i] Editor’s Note: “Broodstock,” also known as brood fish, refers to fish of a particular species that have reached sexual maturity and are capable of breeding.

[ii] Such as building dams.

[iii] According to the law, rivers that are water-drinking sources should be protected, though frequently they are not.

[iv] Maotai Wine is known as the “national wine” and is a large revenue earner.

For further reading on this issue, see:

Battling against the current

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