China Aquatic Products Channel reported that recently, typhoons "Maria", "Mountain God" and "Ambi" have landed in China one after another, causing disasters to fishermen and marine aquaculture enterprises along the southeast coast, causing serious economic losses. Whenever a typhoon disturbs, a large number of fishing rows and cages along the coast are destroyed, and fragments float everywhere, which not only seriously damages the local fishing economy, but also has a serious impact on China's offshore ecological environment.
In response to the impact of natural disasters such as typhoons, the domestic seafood aquaculture industry has been exploring countermeasures. In the past 30 years, China has vigorously developed deep-water cage technology, continuously increased unit output, improved the quality of aquatic products, especially in resisting typhoons and harsh sea conditions. In May this year, the world's largest full-submersible cage "Deep Blue No. 1", designed by the Ocean University of China and other research institutes, was completed in Qingdao, Shandong Province. In June this year, China Shipbuilding Industry Wu shipbuilding group built China's first three super large fishery breeding equipment for the South China Sea "Hainan Lingshui Deep Sea Fishery Breeding Platform" began construction, designed to withstand a maximum of 17 typhoons.
In 1973, China's freshwater cage culture was successful and promoted, and at the same time gave birth to marine cage culture; in 1980, Guangdong Huiyang and Zhuhai opened China's seawater cage culture industry, and quickly spread to all coastal areas.
In relatively deep seas (usually more than 20 meters in water depth), deep-water cage culture is carried out, which has a strong ability to resist wind, waves and sea currents. The structure of deep-water cages is mainly composed of cage frames, aquaculture mesh coatings, anchorage systems and supporting facilities (underwater monitoring, automatic feeding, automatic fish collection, water quality monitoring, high-pressure net washing machinery, etc.).
The deep-water anti-wind and wave cage culture mode integrates computer control, new materials, anti-seawater corrosion, anti-ultraviolet (anti-aging), supporting mechanical instrument manufacturing and other technologies into one.
Deep-water cages refer to aquaculture cages that can be used in deep and open seas (depths greater than 20 meters), which have significant advantages such as environmental protection, durability and wind and wave resistance compared with traditional offshore cages. In recent years, the relevant departments of the state have formulated policies to restrict offshore cage culture and support deep-sea aquaculture, encourage the expansion of aquaculture areas, reduce environmental pressure, and adjust the structure of marine aquaculture species.
Huang Liuyi, a professor in the Fisheries Department of the College of Fisheries of the Ocean University of China, said that the deep-water cage water body is large, closer to the natural environment, and the fish activity range is wide and the survival rate is high. In deep waters, fish grow faster, have fewer diseases, and are closer to wild in size and flesh. The use of deep-water cage culture can not only reduce environmental pressure, but also improve the yield and quality of cultured species.
In particular, deep-water cages have significant advantages in terms of typhoon resistance and harsh sea conditions. Under harsh sea conditions, if the aquaculture cage is settled to a certain depth, the breeding equipment and breeding objects are relatively safe. Although the promotion of deep-water cage technology seems to be a natural success, it is not smooth in practice.
In September 2011, the two major typhoons of Nasha and landed in Hainan, and the deep-water aquaculture cages in Lingao County, Hainan Province, were almost completely destroyed, and more than 1,800 deep-water cages were destroyed in only 3 of them, with a loss of up to 800 million yuan. Tracing back to the source, mainly because the cage anchorage at that time used the "wooden pile" plus "cable" fixing method, rather than "iron anchor" plus "cement pier", which could not resist the super typhoon head-on.
In addition to the anchorage system, the wind and wave resistance of the cage also involves many aspects, such as the frame material, mesh design, and hydrogeological environment.
After several years of hard work, the South China Sea Fisheries Research Institute of the Chinese Academy of Fishery Sciences has made important progress in the design of deep-water cages against wind and waves, and has withstood the test in the invasion of super typhoon "Rainbow" in 2015. The wind and wave resistance design of this deep water cage is not only comprehensive, but also has many refined designs. For example, the anchor weight of the anchorage system is not less than 700 kg, and the angle between the anchor rope and the seabed is less than 27 degrees. The cage frame is made of high-strength materials, taking into account the perennial wave length and aquaculture capacity of the sea area.
Huang Liuyi told reporters that the study of the dynamic response of deep-water cages under the action of wind, waves and currents is the basis and basis for determining the design and safe use of deep-water cages. Foreign new cages must undergo layers of assessment such as model tests, numerical simulations and on-site verification before they can be promoted. With the engineering equipment of cage culture facilities going to the deep sea, the research on large-scale development, cage water power, wind and wave resistance, flow resistance and structural safety has received more and more attention.
On May 4, the world's largest full-submersible cage "Deep Blue No. 1", jointly designed by the Ocean University of China and Hubei Ocean Engineering Equipment Research Institute and built by Qingdao Wuchuan Heavy Industry Co., Ltd., was launched in Qingdao, with a circumference of 180 meters, a culture of 50,000 cubic meters of water, and a single culture of 300,000 salmon.
On June 28th, China Shipbuilding Industry Wuchuan Group built China's first three super large-scale fishery breeding equipment for the South China Sea", "Hainan Lingshui Deep Sea Fishery Breeding Platform", was built in Qingdao, marking that China's far-sea fishery aquaculture will enter a new stage. The platform is a hexagonal steel frame structure with a diameter of 110 meters and a height of 75 meters, which can cultivate 10 million golden pomfrets at a time. The design of the platform fully takes into account the harsh sea conditions in the South China Sea, which is semi-submersible culture under conventional sea conditions, and sinks to the bottom in bad sea conditions to resist 17 typhoons. The platform can realize unmanned remote control farming, with fish feed stocking, live fish fishing, dead fish collection, mesh cleaning, platform monitoring and other functions.
According to industry insiders, in recent years, the technical performance of deep-water aquaculture cages has been continuously improved, and new technologies such as new materials, corrosion prevention, stain prevention, and ultraviolet resistance have been applied. The cage volume is becoming larger and larger, and new materials such as high-density polyethylene, light high-strength aluminum alloy and special stainless steel have greatly improved the overall strength of the cage and doubled the service life of the cage. With the development of computer integration and automatic control technology, cage culture management is more intelligent, which greatly reduces labor costs.
A few days ago, an enterprise in Hainan Province released the news that the lifting cage produced by the company can resist a 18-level typhoon, and the cage can drop to the design depth in as long as 5 minutes, and can operate multiple lifting cages synchronously by 1 person, which can react quickly to typhoons. The person in charge of the company said that the lifting cage has a large price advantage and simple operation in similar products, and has been selected by some large-scale marine aquaculture enterprises in Hainan and other places.
At present, with the increasing pressure of the marine ecological environment and the declining fishery resources of traditional fisheries, deep-water cage technology has attracted the attention of all countries in the world, Australia, Japan and Northern Europe, North America, the Mediterranean and other countries and regions have been widely used, China's Guangdong, Hainan and other places have also promoted the use of a large number of deep-water cages. Even so, the popularization of deepwater cage technology still faces bottlenecks.
The first is the high cost constraint. In the long run, deep-water cages have the characteristics of safety, environmental protection, durability and intelligent operation, which can reduce equipment losses, reduce labor costs, and improve corporate profits. However, China's marine aquaculture industry is still dominated by small-scale aquaculture enterprises and family farmers, and the high price of deep-water cages seriously restricts its promotion and popularization. Among them, the price of the smallest deep-water cage needs to be more than 50,000 yuan / only, and the price of deep-water cages with a circumference of 60 meters, 80 meters and 100 meters is 150,000 yuan / only - 200,000 yuan / piece. In particular, large deep-water cages with new materials and technologies are more expensive. The high costs make it difficult for small and medium-sized aquaculture enterprises to bear.
In addition, China's deep-water cage technology and quality need to be improved. The quality of the connection pipes and fittings of some lifting cages is not up to standard, and the trace air leakage of pipelines and valves causes the cage to sink itself. Monitoring systems and automatic gas compensation devices also need to be improved. The problem of deep-water cage deformation cannot be ignored, and the volume loss rate of the cage in the case of water flow of 1 m/s in ordinary gravity cages is as high as 80%, which greatly compresses the aquaculture water body and is not conducive to fish growth. Mesh cleaning and replacement mainly rely on manual operation, underwater operation is more difficult, anti-fouling technology needs to be improved.
At present, there is still a certain gap between China's deep-water cages and foreign advanced levels in terms of facility construction mode, cage anti-wind and wave resistance performance and structural safety research theory, supporting facilities and technology research. At present, the species suitable for deep-water cage culture are mainly fish, including large yellow croaker, perch, golden pomfret, American redfish and cobia, etc., shrimp and shellfish are less used, and the selection of cultured species needs further research for large-scale cage culture in the deep sea.
Despite the difficulty of promotion, typhoon-resistant deep-water aquaculture facilities still have development potential that cannot be ignored. It is believed that with the improvement of technology, the application of new materials, and the support of relevant policies, deep-water cages will play an increasingly important role in the development of marine fisheries in the future.