Fuxian Lake is not only rich in water resources, but also has excellent water quality. The lake is like jasper, and its color is impeccable. According to the water quality monitoring standards, the water quality of Fuxian Lake is rated as Class I water all the year round. The transparency of the water body is 5~ 1 1 m, and the maximum purity can reach 12.5 m, which gives the fish in the lake a visual sense.
Recently, a large number of fish have gathered on the surface of Fuxian Lake, which is called "herring array" locally, and the spectacular scene has also alarmed CCTV media.
The style of "Herring Array" is undoubtedly revealed in the aerial video. In the video, a large number of herring swim freely on the lake, with different specifications and sizes, and the number is estimated to be hundreds. The scene is quite spectacular. It is worth mentioning that the "herring" mentioned by the locals is not the herring that eats snails among the four major fish, but the original fish in the lake: Spinibarbus yunnanensis, an indigenous fish in Fuxian Lake, and one of the most important catches in the last century.
According to Chen, a local villager, the herring in the lake sometimes gather for several hours and will not disperse until around 5 pm. During the rally, the herring group reacted very keenly. When someone approached, it quickly dispersed and disappeared into the water. The old man also revealed that the "herring array" often appears from May to September every year, and the largest herring weighs 10 kilograms.
So, how did the "herring array" form? Why is it so rare?
In fact, "herring array" is a natural phenomenon, which may be related to two factors.
First of all, the "protagonist" Spinibarbus yunnanensis has the habit of gathering and preying, and the active period is from May to August every year.
Secondly, Spinibarbus yunnanensis feeds on filamentous algae and aquatic plants. Under the influence of light conditions, its food is mainly distributed in the surface layer of lake water and shoal area. However, every summer, the food intake of young and adult fish increases, and for the need of foraging, herding behavior appears.
Some netizens speculate that it may be related to reproduction or lack of oxygen. In fact, the possibility of both is not high.
The possibility of hypoxia is not high, because Fuxian Lake is a stratified freshwater lake with a transparency of 5~ 10m. The lake is characterized by low organic matter content, which can ignore oxygen consumption factors such as "water respiration", and has sufficient dissolved oxygen during the day and no hypoxia.
Fuxian Lake is also a deep-water lake, with an average water depth of more than 90 meters and the deepest point 155 meters. Indigenous fish in the lake have a vast habitat, low fish density and low oxygen consumption. To take a step back, even if there is hypoxia, the time to float the head should be around the morning (at this time, the dissolved oxygen in the water is the lowest), and the time when the "herring array" appears is noon and afternoon, which is obviously inconsistent with the time of hypoxia.
As for the "rare" reason, local residents also told the truth: it is related to artificial fishing. Since 1970s, the fishery in Fuxian Lake has been developed to a high degree, and the wild resources have declined seriously. In recent years, through orderly fishing ban, proliferation and release, the natural population has gradually recovered, and the frequency of "herring array" has increased.
A large number of fish schools are concentrated, which at least shows that Fuxian Lake is rich in fish resources. In the fishery investigation in190' s, there were 25 species of indigenous fish recorded in Fuxian Lake, among which the most classic was Spinibarbus yunnanensis, which played the role of "herring array", followed by? ? Wave white fish
Indigenous fish is a major feature of Fuxian Lake, which has contributed considerable benefits to fishermen in the lake area. In the 1980 s, the light-lipped fish in Yunnan Lake, There are also a large number of white fish, Fuxian golden thread fish and so on. , is the main fishing target. Now the situation is very embarrassing, and all of them cannot form fishery output.
With what? ? Take white fish as an example. The' 80s? ? The annual output of whitebait is stable at 300~400 tons, and it dropped sharply in the 1990s. According to the statistical data of 1998, only white fish 10.4 tons was produced in that year, and the income of fishermen and civilians can be described as "bleak". The situation of resource depletion has not been reversed. From 2000 to 2004, its output further decreased to 0.5~ 1 ton. Once dominated? ? The advantage of Bobfish is no longer, and the old aborigines are in great crisis.
In sharp contrast, the number of exotic fish in Fuxian Lake is increasing, and whitebait is "anti-guest-oriented" within 10 year, which has greatly seized the niche of whitebait and become a new dominant species.
According to the records of the fishery department, there were two large-scale introduction activities in Yunnan Province in the last century. The first time was in the 1960s, and the second time was in the 1980s. Dianchi Lake, Erhai Lake and Yangzonghai Lake were all introduced as "virgin lakes".
1982, the new whitebait in Taihu Lake was introduced into Xingyun Lake, just across the embankment from Fuxian Lake. Unexpectedly, this rare fish, which is transparent and only 5~8cm long, entered Fuxian Lake across the river and formed a stable population in just a few years. 1990 to 2004, whitebait proliferated explosively, with an average catch of 1554 tons, completely replacing the endangered whitebait? ? Wave white fish
On the one hand, whitebait can devour fish eggs and zooplankton in the lake and compete for it? ? Food resources and habitat space of white fish; On the other hand, the fishing method of whitebait also makes? ? White fish lying gun for no reason. According to the trawl survey results in 1980s and 1990s, for every new whitebait 1000g in Taihu Lake, fishermen in the lake area will catch 250 together. ? Bobfish, only 2~4cm in size, is obviously in the juvenile stage.
Long-term fishing for whitebait? ? The juvenile resources of whitebait are decreasing, and the population size is shrinking. Thank god, artificial breeding has been given? ? Bobfish brought a life-saving straw, and other indigenous fish also got a "new life after robbery". For example, the goldfish and whitebait in Dianchi Lake, Yunnan Province have been extinct for many years, and the population extinction is also prevented through artificial breeding.
The indigenous fish in Fuxian Lake are still in crisis, and the natural population has not fully recovered. We should avoid blind introduction and transplantation again, strengthen ecological protection and leave a pure land for indigenous fish.
Fuxian Lake is a veritable "Pearl of the Plateau" with good water quality and good ecology, but Xingyun Lake, located in the southwest of Fuxian Lake, is a different scene: the lake area is green due to serious eutrophication, the density of cyanobacteria remains high, and the water quality is inferior to Grade V and V all the year round, which is in sharp contrast with Fuxian Lake.
The comprehensive nutritional index shows that Xingyun Lake is a nutritious lake with high nitrogen and phosphorus content, which is not unrelated to fish farming activities in the last century. In order to develop fishery economy, Xingyun Lake was widely introduced in the last century, involving four major fish, carp and whitebait, many of which spread to Fuxian Lake.
According to the historical introduction data, Fuxian Lake only introduced 6,543.8+100,000 grass carp in 1966, and there were no other introduction activities since then. However, in the investigation, the number of exotic fish in the lake is increasing, and in 2004, the number of exotic fish has reached 19. It can be inferred that most of the exotic fish in Fuxian Lake should come from Xingyun Lake.
In addition to exotic fish, the water quality of Xingyun Lake also has a potential impact on Fuxian Lake. Topographically, Xingyun Lake is the upstream lake of Fuxian Lake, and the water of the former may become the pollution source of the latter. Therefore, the protection of Fuxian Lake should attach importance to the sewage treatment of Xingyun Lake, optimize the outflow and diversion project, strictly control the direction of water flow, and be alert to the threat of rain and flood pollution.
Fuxian Lake has an important water storage function. Because of its strong sealing, the theoretical water exchange period is as long as 167 years. Therefore, once the lake area is seriously polluted, it is difficult to repair it in a short time.
As far as water source is concerned, Fuxian Lake is mainly replenished by rainfall and runoff, and there are 103 rivers in the basin. Water quality management can start from the following aspects:
First, strengthen the source control of pollutants such as nitrogen and phosphorus, strengthen the control of important waters such as rivers and Xingyun Lake in the basin, and eliminate inferior water bodies.
The second is to take biological water control measures. For example, increase the number of silver carp and bighead carp in Xingyun Lake and Fuxian Lake? ? Releasing native fish, such as whitebait, will restore their niche. In the lakeside area, we can increase the planting of submerged plants, repair and improve wetlands, and improve the water purification capacity.
The third is to strengthen water quality monitoring. Fuxian Lake has a huge water storage capacity, which is equivalent to 12 times that of Dianchi Lake and 6 times that of Erhai Lake. In order to ensure the water quality, multiple monitoring sections can be set up in the upstream rivers and lakes, and the water quality can be monitored daily or weekly, so as to form a perfect early warning system and ensure the sustainable existence of clear water in one lake.