Erhai is the second largest plateau lake in Yunnan, once with very rich fishery resources, and is even known as the "hometown of fish and rice" in western Yunnan. Since the 1960s, the indigenous fish in the Erhai Sea have gradually decreased, and the water quality has begun to deteriorate, and the ecology of the Erhai Sea has also fallen into crisis.
Satellite map of the Erhai Sea
From the timeline, the fate of Erhai and many plateau lakes such as Dianchi Lake, Fuxian Lake, and Xingyun Lake is "bound" together, and the indigenous fish in each lake also face a similar fate: overfishing, water environmental pollution, and invasion of alien species. Due to the blind pursuit of economic interests and lack of environmental awareness among surrounding residents, Erhai has issued one "ecological penalty card" after another in the past 40 years, and the losses caused have been irreparable.
In the 1950s, there were 17 species of indigenous fish in the Erhai Sea, common ones are Dali split-bellied fish, Yunnan split-bellied fish, Dali four-whiskered catfish, big-eyed carp and so on. At that time, the fishery production of the Erhai Sea was basically "contributed" by indigenous fish, with a total output of 1500 tons, of which the annual output of Dali split-bellied fish could reach 750 tons, and the production of Erhai four-whiskered catfish could be stabilized at about 300 tons.
Yunnan split-bellied fish
Since 1961, locals have introduced common economic fish species such as grass carp, silver carp and bighead carp into the Erhai Sea, mainly for the purpose of increasing economic benefits. However, people did not notice at the time that the introduced fry were also mixed with small fish such as Chinese salmon, wheat ear fish, stick flower fish, goby fish and so on - this humble detail brought serious harm to the indigenous fish of the Erhai Sea.
These small trash fish that are "smuggled in" have no economic value, and local fishermen do not deliberately list them as fishing targets. The Erhai Sea is rich in aquatic and grass resources and is a natural spawning ground for many indigenous fish. When indigenous fish such as big-eyed carp and Erhai four-whiskered catfish enter the breeding period, small trash fish such as goby and wheat ear fish will enter the spawning grounds to devour a large number of eggs, which seriously affects the natural reproduction of indigenous fish.
Wheat ear fish
By the 1970s, it was difficult to see indigenous fish such as Yunnan split-bellied fish, gray-bellied fish, Erhai carp and Dali carp in the Erhai Sea. Even the highest-yielding Dali split-bellied fish has not escaped doom, and the harvest has "shrunk" sharply. In 1973, the purchase of schizothorax in Dali was less than 15 tonnes, and the amount of resources had decreased by 98% in 20 years. In 1975, the production of Dali schizothia fish fell further to 0.5 tonnes; by 1976, there were only 6.5 kg of Dali schizophrenic fish out of the water.
Erhai fishermen
Just when the indigenous fish in the Erhai Sea are collectively "declining", the small miscellaneous fish from the outside are "flaunting the market" in the Erhai Sea. The humble small trash fish have seized most of the lake's bait resources, forming an extremely large dominant population, with the production of goby fish alone reaching 1250 tons. In just 20 years, the population structure of Erhai fish has undergone earth-shaking changes, and the survival crisis of indigenous fish has become inevitable.
Although the production of indigenous fish in the Erhai Sea had already "declined" in the 1970s, this did not stop the pace of the introduction of new species. By the 1980s, crucian carp had become the most productive economic fish in the Erhai Sea, producing more than 600 tons a year. The ecological habits of crucian carp are very similar to those of Erhai carp and big-eyed carp, so they have not had much impact on the survival of indigenous fish. The real devastating blow to indigenous fish was the introduction of the new SilverFish of Taihu Lake in 1984.
Taihu new silverfish
It is worth noting that also in 1984, the production of silver fish in Yunnan's largest lake, Dianchi Lake, reached 3,500 tons, setting a record for the highest production of economic fish species in Dianchi Lake. For fishermen, silverfish have a higher economic value and lower operating costs, and only need to purchase fertilized eggs from other places and stock them directly into the lake. The successful transplantation of silver fish in Dianchi Lake received unprecedented attention, and a "silver fish fever" swept across the country (especially after 1995).
At its craziest, more than 90% of the plateau lakes in Yunnan Province were transplanted with Taihu silverfish, and the Erhai Sea was no exception. The real production of silverfish in the Erhai Sea was in 1991, when the production was 530 tons. Surprisingly, however, since the "settlement" of silverfish in the Erhai Sea, the production of bulk freshwater fish such as bluefish, grass carp, silver carp and tuantou bream in the lake has begun to decline, and the overall comprehensive income of fishermen has not increased significantly.
New silverfish in Taihu Lake with different sizes
From the perspective of feeding habits, the new silverfish in Taihu Lake mainly feed on zooplankton in the water, such as rotifers, branches, copepods, etc., but also swallow the eggs of indigenous fish. As a result, in waters where silverfish are proliferating explosively, the production of other fish species is often minimal.
In addition, the lifespan of the new silverfish in Taihu Lake is only one year, the parents will die after breeding, and the decomposing corpse has a great impact on water quality. It is precisely because of this that in recent years, in the context of the Year-round Closure of the Lake in the Erhai Sea and the ban on fishing, the local government still allows fishermen to catch silver fish, which not only achieves the rational use of resources, but also reduces water pollution, which can be described as killing two birds with one stone.
Researchers have done such an experiment, the dead silver fish into the pond with grass carp and carp, the result is that after a while the live fish in the pool began to die; in another pool where the silver fish were not placed, the carp and grass carp were safe. It turns out that after the silver fish dies, the protein will consume dissolved oxygen in the water when it is decomposed, causing other fish to suffocate to death. Judging from this result, the regular "salvage" of silver fish in the Erhai Sea is also quite necessary.
When the natural catch of the Erhai Sea decreases, local fishermen often blindly increase the number of boats, reduce the size of the net, and prolong the fishing time in order to increase economic income, which directly leads to serious negative effects: many sexually mature fish are "exhausted", and the problem of miniaturization and juvenile of catches is becoming more and more serious.
After the successful transplantation of silver fish, the number of motorized fishing boats in the Erhai Sea also increased dramatically. In 1985, there were only 519 fishing vessels in the Erhai Sea, and in 1995 it suddenly increased to 5488, of which 2625 were motorized fishing boats. In order to catch more silver fish, local fishermen generally use dragnets, trawls, silk nets and other fishing methods, and there are often many juvenile shrimp in the nets – all of which are eventually transferred to the market for sale indiscriminately.
In the 1990s, many farmers around the Erhai Sea began to reclaim the beach land of the Erhai Sea into farmland (covering an area of 4,776 mu), and some people converted the mudflats into fish ponds (covering an area of 3,035 mu). Since 1992, in response to the "Vegetable Basket" project, many aquaculture cages have appeared on Dianchi Lake, and farmers have raised fish to generate income by harvesting aquatic weeds and feeding feed. At its craziest, there were 7,714 large and small cages in the Erhai Sea, which consumed a lot of aquatic weeds and feed every day.
This has been going on for 4 years, and the eutrophication pollution of the Erhai Sea is getting worse and worse. In the autumn of 1996, the Erhai Sea for the first time erupted cyanobacteria caused a "bloom", which caused a huge sensation at the time. In 1997, the local government urgently banned motorized fishing boats and fish cages in the Erhai Sea, and imposed strong controls on overfishing, but this did not fundamentally solve the crisis faced by the indigenous fish species in the Erhai Sea.
Today, the pollution control of the Erhai Sea has become a big problem, and the local government even plans to invest 3 billion yuan to make the Erhai Sea meet the standard of Class II water quality. The plan includes garbage and domestic wastewater treatment in 200 villages, the construction of 30,000 mu of wetlands, and the "100 million square clean water into the lake" project, and the specific effect remains to be seen.
In short, "green water and green mountains are golden mountains and silver mountains", compared with economic interests, the water environment of Erhai Sea is always the best ecological welfare. Whether the governance of The Erhai Sea can be a great success, we will witness it together!
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