The Qiantang River is a very important river along the southeast coast of China, and it is also the largest river in Zhejiang Province. According to statistics, in the basin area controlled by the Qiantang River, the land area accounts for 47.2% of Zhejiang Province, and the GDP accounts for 64.1% of Zhejiang Province, which can be called a "financial river".
Qiantang River
The Qiantang River basin includes not only the Qiantang River, but also the Xin'an River, the Fuchun River and the Lan River (all four of which are located in the main stream), and the main tributaries in the basin are mainly the Fenshui River, the Cao'e River, the Wuxi River, the Wu river and the Puyang River.
Historically, the Qiantang River basin is very rich in fishery resources and is an important spawning ground for anchovies and knifefish. In addition, the triangular bream (locally known as tower bream) and the Ziling snouted goby (locally known as Ziling fish) here are also quite famous and have a long history of fishing.
According to the old fishermen's recollection, in the past, every spring, flocks of knife fish would breed on time, swimming all the way to Xiasha, Qianjiang Bridge and the lower reaches of the Fuchun River, which was very gratifying. The knifefish of the Qiantang River are not as famous and resource-rich as the knifefish of the Yangtze River, and the survival crisis of the population also appears earlier. As early as the 1970s, the Qiantang River knife fish could not form a fishing flood, and it was basically extinct in the 1980s.
Yangtze River knifefish
According to literature, a total of 238 species of fish were found and recorded in the Qiantang River basin in the last century. Among them, migratory fish account for a relatively high proportion of the total catch and are the most important fishing objects in the Qiantang River basin. Anchovies, knifefish, eels and four large fish are all migratory fish.
In 1959 and 1968, the Xin'an River Reservoir and the Fuchun River Reservoir were built in the Qiantang River Basin, which caused a huge impact on the ecology of the river, with migratory fish bearing the brunt. Surveys show that in the area of the Qiantang River and Fuchun River, the area of fish spawning grounds has decreased by about 2/3, the fishery production is only 1/10 of the past, and the valuable fish such as knife fish and anchovy have decreased significantly.
Before the dam was built, the highest production of anchovies in the Qiantang River had reached 85 tonnes, which had dropped sharply to 270 kg in 1981 and 35 kg in 1983. By 1984, only four anchovies were caught in the whole river, weighing less than 5 kilograms in total, and they were basically sentenced to "death". In the same period, the production of anchovies in the Yangtze River was barely about a dozen tons, but it was also not optimistic.
Qiantang River fishermen
The fate of anchovies and knifefish is just a microcosm of the ecological changes in the Qiantang River, and the impact of the reservoir dam has also affected other fish. Taking the Xin'anjiang Reservoir as an example, before the completion of the hydropower station, there were 107 species of fish here, and after the completion of the reservoir, the number of fish gradually decreased to 83 species, and 24 species of fish disappeared before and after.
Not only that, but the flooding causes large-displacement low-temperature water bodies to pour into the downstream, bringing disaster to the warm water fish. Since 1963, on the section of the river about 15 kilometers from the Xin'an River Dam to Mamu, the warm water fish of the four major fish have almost disappeared, and the cold-water fish such as rainbow trout transplanted from abroad have grown well.
Xin'an River flood discharge
But then again, the completion of the reservoir also has many benefits. The primary function of water conservancy projects is flood storage and flood prevention, to ensure the safety of people's lives and property downstream, and also has the social benefits of agricultural irrigation, power generation and shipping.
It is worth mentioning that after the damming river is stored, the water capacity in the Xin'an River reservoir area is increasing, and the water surface is becoming wider and wider. In the upper layers of the water body, the phytoplankton are well illuminated, the base food is very rich, forming a superior breeding platform, and the fishery production has increased by more than 30 times compared with the past.
The largest contributors to production are silver carp and bighead carp, which account for more than 70 per cent of total fishing production in the reservoir area. In order to manage the reservoir fishery well, the local fishery will release a large number of silver carp fry every year, this "tradition" has continued for more than 50 years, and now it has become a model of "water-retaining fishery", which is promoted nationwide.
Chun brand organic bighead fish
Throughout the 1980s, the Xin'anjiang Reservoir area averaged more than 500,000 kilograms of large-sized fry per year. In recent years, the stocking of fish fry has further increased to more than 600,000 kilograms, and the industry has become bigger and bigger. Chun'an County's "Chun" brand organic silver carp is well-known throughout the country and is recognized by the market.
In 1984, the Xin'anjiang Reservoir was renamed Qiandao Lake. It has to be admitted that the fish farming model of Qiandao Lake has indeed had a profound impact on the country's large surface fishery, but there are also some new problems in the process of fishery development, and the more prominent performance is the invasion of alien species.
According to statistics, from 1986 to 2020, the local fishery introduced and released more than ten species of exotic economic fish to Qiandao Lake, the main species include sturgeon, sturgeon, nile tilapia, silverfish, spotted forktail catfish, blue gill sunfish and so on. Some of these exotic fish have been successfully bred in Qiandao Lake and formed a certain scale, which has a potential negative impact on the original ecology of the Qiantang River Basin.
Spotted forktail catfish
Take, for example, the spotted forktail catfish. Native to the southern region of North America, this fish is one of the most important freshwater fish cultured species in the United States. The water quality environment of Xin'an River is very similar to the origin, which provides good conditions for the survival and reproduction of the spotted forktail catfish.
The spotted forktail catfish itself has the characteristics of strong adaptability, fast reproduction, wide diet, etc., and the market price is also very high, which is very popular with cage farmers (most of the cages have now been cleared). In the past, due to the large breeding base, escape events occurred from time to time, which gradually spread to the upper reaches of the Xin'an River, and juvenile individuals have been found in the southeast lake area and the northwest lake area.
Two other "climate-forming" alien species are the blue-gill sunfish and the silverfish.
The origin of the blue sunfish is the Mississippi River Basin and the Great Lakes region of the United States. This fish can adapt to water temperatures of 1 to 38 ° C, is aggressive and reproduces quickly. Years of investigations have shown that the gonads of the blue sunfish are able to develop normally in the reservoir area each spring, and once the species naturally multiplies and spreads in the lake, it is highly likely to become the most dangerous invasive species, with immeasurable effects on native fish.
Blue gill sunfish
As for the silverfish, the local fishery was transplanted from Taihu Lake between 1999 and 2000, and the species is the Chen's short-snout silverfish. Individuals of silverfish are small and only have a one-year lifespan, but they are also very threatening to devour the eggs of other fish and seize the ecological niche.
Originally, the staff released the fertilized eggs of the silver fish directly into the lake, and after natural hatching, a considerable population was formed. The harvest of silver fish is very special, in order to obtain a stable yield, it is necessary to transplant fertilized eggs every year, once the transplantation is stopped, the population resources will decline rapidly, and prevention and control is relatively simple.
So far, these exotic fish have not caused an existential crisis for native fish (at least not reported in the media and journals), but there is no doubt that the phenomenon of invasion has occurred. Some experts remind that species such as spotted forktail catfish and blue gill sunfish are extremely likely to spread in the Qiantang River Basin, and it is necessary to further strengthen breeding monitoring and investigation in order to carry out human intervention in a timely manner.
In accordance with the regulations of the State and Zhejiang Province on the protection of animals and plants, the necessary anti-escape measures should be taken when introducing and breeding alien species. For the more threatening carnivorous fish, it is best to achieve fully enclosed breeding and strict supervision to prevent escape incidents.
In addition, it is particularly important to improve the public's awareness of ecological protection and standardize the release behavior. In the Qiantang River Basin and even the whole country, the phenomenon of blind release is relatively common, and scientific guidance can truly benefit the ecology, otherwise it is a disguised "killing".
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