There is a Xin'an River hydropower station in Chun'an County, Hangzhou, and when the hydropower station was built, it intercepted the upper reaches of the Xin'an River to store water, forming the beautiful Qiandao Lake, that is, the Xin'an River Reservoir. There are a total of 1078 large and small islands in the reservoir, hence the name Qiandao Lake.
Qiandao Lake is actually the Xin'an River Reservoir, which is formed by the interception and storage of water by a hydropower station
Qiandao Lake has clear water, beautiful scenery and excellent water storage, which can reach 17.8 billion cubic meters.
In this lake, there are more than 1,700 kinds of plants, nearly 100 kinds of fish, and there are many artificial farms, such as grass carp, silver carp, bighead carp, mandarin carp, eel, blue carp and other commercial fish with high economic value.
But don't look at the rich natural resources of Qiandao Lake, in fact, it also faces problems. Bighead carp, silver carp, grass carp and blue carp are the famous four big fish in the mainland, but many of them in Qiandao Lake are stocked for water retention, and when these fish grow up, people find two problems: one is difficult to fish, and the other is difficult to stock.
Many fish in Qiandao Lake were originally stocked to preserve water
Why is that? What aspects of Qiandao Lake were preserved by the original water-retaining fish?
Fish water retention program
Since Qiandao Lake is a reservoir formed by interception, there is water storage and water release.
When the water is released, the fish in the lake are washed downstream with the current, and the fish resources in Qiandao Lake will decrease; When the water is stored, although the fish can grow, the plankton and various algae in the lake will also flood.
For example, one of the most troublesome problems in fresh water is the bloom crisis caused by cyanobacteria, which refers to the excessive growth of cyanobacteria, covering the water surface, destroying water quality, reducing oxygen content in water, and forming a substance called "lake indigo".
The bloom crisis caused by cyanobacteria outbreaks causes indigo to form on the surface of the lake
The ponds we often see in rural areas have thick green algae floating on them, which smell foul, which is the phenomenon of blooms. This is usually the result of the absence of fish in the water and the pond being left unattended for a long time.
Among the four large fish, except for the blue fish is a carnivore, the other three are mainly herbivores, eating more algae, debris and some bacterial aggregates, and eating some small plankton, such as rotifers, nauplii, earthworms and so on. Moreover, grass carp, silver carp and bighead carp are not small in size and eat a large amount, so these fish are raised more in fresh water, which is very helpful to maintain water quality.
The dietary habits of the four big fish are very helpful in maintaining water quality
Since 2006, there has been a problem of overgrowth of algae in the water storage of Qiandao Lake, and a large number of conchochophytes and bundled filaments cover the lake surface, and the density is so high that it threatens the water quality. As a result, the relevant departments came up with a plan to use fish to retain water.
Later, Qiandao Lake had a high-yield fish farm, and silver carp, bighead carp, etc. could be self-sufficient in the lake without artificial feeding. The fish grown up in this way have not eaten feed, so the meat is delicious, the price in the market is also high, and the organic fish brand here is also certified by the state, even if it is expensive, it is very popular with consumers.
Organic fish from Qiandao Lake has become a regional feature
Difficult stocking problem
Buyers don't have to worry, but stocking fish is worrisome. Many onlookers who do not know the truth believe that there is nothing to consider if there is no fish in the water.
But in fact, stocking fish in the water is never a simple matter, and there are many factors to consider, such as when to put it, how much to put it, and how much to account for each type of fry, which must be calculated, otherwise it will cause an ecological burden, or the fry will not survive.
More than 60 years after the Xin'anjiang Reservoir was completed in 1960, the problem of stocking fish has not been solved. It is not because the four large fish feed on each other, but the fish that eat planktonic algae do not live in perfect harmony, and there is competition among them, resulting in the inability to ration the fry.
Many of the fish species sampled in the waters of Qiandao Lake are competitive
What's going on here? Could it be that there are not enough plankton in the Thousand Island Lake for them to eat?
This is indeed one of the reasons, every year water storage and release, the lake water is changing, the algae reproduction is also different, how many fish to put, you must first assess the water quality, not how much you want to put and how much.
For example, if the algae overgrows, the stocking of bighead carp can be reduced, and the proportion of silver carp that eat more algae than bighead carp can be increased.
Bighead carp (top) eat a little less algae than silver carp (bottom).
Another aspect to note is to consider how many fish are present in the water, but this number cannot be counted.
For example, silver carp, which usually lives in the upper layer of the lake, and when the water surface falls back during the dry period of winter, it also hides at the bottom of the lake for the winter, and is not very active throughout the winter. Therefore, how many fish are in the lake cannot be seen or counted, and only a rough measure can be made based on the annual catch.
But there is also a troublesome problem, in the spring and summer, these fish enter the breeding period, it is not clear how many eggs are laid, how many eggs are alive, let alone know, the fry are too small to catch, so how to measure how much should be stocked next time according to the amount of catch?
The proportion and quantity of fish stocked in Qiandao Lake are not easy to control
If it is less, the fish production will decrease, which will not only affect the income of the fishery, but also may give algae the opportunity to grow wildly, which in turn will affect the living environment of the fish, causing the fish production to decrease again.
Fishing is difficult
In addition to the problem of difficult stocking, fishing in Qiandao Lake is not easy, don't look at its rich fish resources, but fishing is quite difficult.
This effort does not mean how difficult it is to catch fish, but how difficult it is to catch the right fish. Because the fundamental purpose of these fish stocking is to retain water, to maintain the ecological balance of Qiandao Lake, the amount of fishing is regulated, and the size of fish is standard.
There are standards for the number of fish caught in Qiandao Lake, as well as the specifications of fish
Fish that have not grown to a certain size cannot be caught, so they have to be put back and allowed to grow for another two years. But the fishing net has no eyes, and all kinds of fish are scattered into the net, so after catching it, it is necessary to manually check and release the small fish. One more process is to increase labor costs, of course, it is difficult.
Moreover, the geomorphological environment of Qiandao Lake is complex, there are small basins, hills, valley floors, etc., some fish have become old fritters after living in the lake for a long time, knowing that fishing boats are coming to hide, where to hide, it is completely familiar with the road. Therefore, when fishermen are fishing, it is difficult to catch big fish.
The geomorphological environment of Qiandao Lake is complex, and fish are easy to avoid
No one can say how big the fish in Qiandao Lake can grow so far, for example, blue fish love to hide at the bottom of the lake, the deepest part of Qiandao Lake is more than 110 meters, blue fish are not easy to catch, usually caught are silver carp and bighead carp, although a hundred pounds of silver carp have also been caught, but so far, the largest fish caught by fishermen is bluefish.
In 2015, some fishermen found that there was a super large blue fish struggling in the net when they closed the net, and the flapping tail almost knocked down the person next to them, and then everyone worked together to hold down the big blue fish, and when they looked at the scale, it had a full 180 pounds, which was definitely the king fish produced by Qiandao Lake.
Qiandao Lake "King Fish" caught in 2015
Prior to this, the fishermen had caught 151 and 120 pounds of large fish. However, in addition to hiding such a large fish, it is difficult to grow, at least 7 years. Qiandao Lake can catch 8 million jin a year, and it is impossible to wait for the fish to grow so big.
Such a large amount of fishing is also the reason why Qiandao Lake regularly releases fish fry, these fish are released, which not only purifies the water but also brings huge benefits, killing two birds with one stone, and preserving the ecological and economic benefits of Qiandao Lake.
The fishing volume of Qiandao Lake is actually very large, and regular release of fish fry can increase the economic benefits of Qiandao Lake
At present, the water quality of Qiandao Lake is better than the tap water sources in many places, and it perfectly interprets what is the harmonious development of man and nature.
Of course, this ecological breeding method is worth promoting, but first of all, it is necessary to conduct in-depth research and actively solve the two major problems of stocking difficulties and fishing difficulties, so that the method can be effectively replicated in other places.
The ecological breeding method of Qiandao Lake is worth promoting, and the conservation value of biodiversity is very important
So do you have any tricks for problems similar to the two difficulties of Qiandao Lake?