In China, there is low pressure in spring and storms caused by typhoons in summer. In autumn and winter, cold air from the north moves south, leading to the north wind. Strong winds and huge waves bring great difficulties to ship navigation and fishery production, especially in the fishing season, which will delay the opportunity and affect the high yield of fishery.
Fishermen in China thoroughly understand the "temper" of marine fish in practice, analyze the relationship between wind and fish with the viewpoint of "one divides into two", and insist on "grabbing the limelight and catching the tail of the wind" in order to win a bumper harvest of marine fisheries.
As we all know, before the gale comes, the air pressure drops, and waves are generated at sea, and the speed of wave propagation is faster than that of airflow. Therefore, before the strong wind reaches the fishing ground, there will be waves with fast propagation speed in the coastal fishing ground, and the waves with particularly long wavelength are called "long waves". In addition, the sea level rises and falls due to the sudden change of air pressure. When the air pressure decreases, the seawater converges to the center of low pressure in the horizontal direction, which is called "air pressure wave". Both "long wave" and "barometric wave" are waves, which propagate in the form of waves on the surface. In fact, seawater molecules vibrate violently at their equilibrium positions, and the vibration intensity decreases rapidly with the increase of seawater depth. In order to escape the influence of the violent vibration of the upper seawater, fish swim in droves to the low-pressure central sea to find suitable habitats. Fishermen seize the good opportunity of fish gathering before the gale, grab the limelight, cast more nets and catch quickly, and catch a large number of fresh fish such as hairtail, yellow croaker, squid and shark in one net.
In winter, strong winds blow continuously on the sea surface for a period of time, which will cause vertical agitation and vertical mixing of seawater. The stronger the wind, the longer the blowing time, and the more vertical mixing of the sea surface will spread to the seabed, so that the seawater near the seabed will produce a stronger vortex, which can lift up the tiny seabed sediments and form a fairly thick turbid water layer from bottom to top. In addition, the sudden cooling of the sea surface caused by cold air makes the sea water emit a lot of heat, which further strengthens the vertical mixing of the sea water and makes the sea water in shallow fishing grounds turbid and cold.
Due to the changes of these environmental conditions, the fish that originally lived in relatively clear and warm seawater dispersed. When the wind weakens, the fish has to find its suitable environment, and then the fish has a concentrated process. In the case of strong wind and scattered fish, try not to go to the port island to take shelter from the wind, and take headwind measures on the basis of safety. Once the wind decreases, the fish return to their normal living environment, and once again, when the fish disperse to concentration, the fishermen immediately put into production to seize the high yield after the wind.
The winter fishing season in the East China Sea is the longest season in China. It usually starts in winter and lasts for about three months until it rains or gets scared the next year.
In autumn and winter, the cold air in the north frequently goes south, the warm water in the open sea weakens, and the cold water along the coast expands. Because of the change of marine environment, hairtail, which was originally scattered outside the Yellow Sea and the Yangtze River estuary, swam back from north to south along the coastal waters of Zhejiang, forming a hairtail fishing ground in the East China Sea in winter. It starts from Sheshan and Huaniao Mountain outside the Yangtze River estuary in the north and reaches Dongtou and Nanbei Deer Island in the south of Zhejiang.
The fishing season is in winter, and the strong cold air in the north often invades the fishing ground southward, which has a great influence on the fishing season in the East China Sea. Because when the cold air goes south, with the northerly wind, the strong wind will set off huge waves, which will affect the fishing boat operation; In addition, due to the sudden drop in temperature, the temperature of seawater drops rapidly, prompting fish to go south. Therefore, if the cold air is strong and frequent during the fishing moratorium, the speed of fish going south will be accelerated, so the number of fishing moratorium days will be reduced accordingly.
However, everything is divided into two. Strong winds have advantages and disadvantages, because the cold air from the south causes the seawater to stir violently, so that the warm water and cold water in the ocean are strongly mixed, forming seawater with different turbidity (called water clip by fishermen), and hairtail is generally clustered in the white water clip; At the same time, due to the strong wind, the sea water near the bottom of the coast becomes turbid, which is not suitable for hairtail habitat, so it floats to the middle and upper layers, driving hairtail clusters to form a central fishing ground, which greatly facilitates the fishing of motorized sailboats and sailboats. Fishermen seize the good opportunity that strong winds can produce water traps and form fishing grounds, cast more nets and catch fish quickly, and often they can catch tens of thousands of kilograms of hairtail in one net and get a bumper harvest. It can be seen that the rhythmic southward movement of cold air can achieve the natural function of strong wind to promote the density of hairtail, which is the beneficial side of cold air to the winter fish season.
In addition, the early and late fishing seasons are mainly related to the cold and warm weather around beginning of winter, and the cold and warm weather is related to the frequency and intensity of cold air going south at that time. Also, when the cold air goes south, if the northeast wind blows, the mixed water system will be pushed to the inner side of the coast, and the central fishing ground will also be inward; If the northwest wind blows, the mixed water system will be pushed out to sea and the fishing ground will be outward. Therefore, the direction of strong wind caused by cold air going south also has a certain relationship with the location of the fishing ground.
There are southeast winds for several days in the long summer, and squid rushes to the mountains.
China has a vast territory, with a coastline of more than 1 10,000 kilometers and more than 5,000 islands. It has a "continental shelf" with flat seabed, accounting for about 23% of the total area of the world's "continental shelf". Coastal aquatic resources are abundant, with more than 500 species of fish/kloc-0 and more than 200 species of main economic fish, making it one of the countries with more fish production in the world.
Fishermen have accumulated rich experience in their daily fishing work and compiled these experiences into fishing proverbs in vivid language. For example, there is a fishing proverb in Zhoushan that "the southeast wind blows for several days in long summer, and cuttlefish (squid) rushes to the mountain". That is to say, in the long summer season at the beginning of May, the southeast wind blows continuously along the coast of Zhoushan, which will cause the water temperature to rise and the water will flow from the southeast coast to the northwest island coast. At this time, the squid is laying eggs, and the eggs should be attached to rocks in the water. In addition, cuttlefish's swimming ability is very weak, so it will swim to the mountain side with the water. In addition, there is a saying that "a storm hits in long summer and the squid collapses". In fishery, "storm" refers to the north wind blowing from the sea, and "anchoring" refers to the squid stopping in place. In the long summer, squid would have swam to Zhoushan Island in the northwest with the current. When the northwest wind blows, the squid moves slowly and it is difficult to form a group, resulting in the phenomenon of "anchoring".
Another example is the fisherman's proverb, "floating in cold and warm, floating day and night, floating in clear water", which means that the water temperature drops, the fish sinks, the water temperature rises and the fish floats; At noon, the sun is strong, the fish sinks, at dawn or evening, the sun weakens and the fish floats; The water is clear, the fish is heavy, the water is turbid and the fish is floating. This is the law of fish movement caused by the contradiction between water temperature, sunlight and water color. According to this rule, fishermen use lights to lure scattered fish into groups, and according to the fluctuation of water temperature and the turbidity of water color, adjust the height of nets appropriately to carry out targeted fishing. This will turn the off-season into the peak season, and the peak season will be more prosperous.
In freshwater fisheries, there is also a saying that "catching running water in hot days, catching deep pools in cold days, full of wind, snowy running water, clear water at night, muddy water at day, catching dawn in the morning and catching dusk at night", which clarifies the contradictory movement law of freshwater fish with the weather and seasons. According to these laws, fishing methods can be adopted according to local conditions.
In short, many fishing proverbs show that the activities of fish schools are influenced by many factors, such as seasons, climate, water temperature, etc., and there are certain changing rules, that is, "there are signs to be found, things to be observed and phenomena to be considered". As long as we carefully observe and study hard, we can grasp the initiative of fishing and vigorously develop fishery production.
The phenomenon of fish swimming north and south in the ocean is caused by the contradiction between the physiological requirements of fish and the changes of marine environment. The group swimming caused by the need to find suitable sea areas for fish reproduction is called spawning migration; In order to find bait, group swimming is called bait migration; Due to the change of seasons, in order to adapt to the water temperature, the group swimming caused by it is called warm migration. Fishermen in China have mastered the migration law of marine fish in long-term production practice. "Fish in the north in three days in spring and fish in the south in three days in autumn" is one of the experiences. This means that marine fish tend to swim from south to north after spring and from north to south after autumn.
With the change of seasons, cold and warm air will move south or north, resulting in the temperature rising or falling. There is a similar phenomenon in the ocean. There is a warm current flowing from the equator to the north, which is called warm current with high temperature and salinity. There is also a cold water flowing south from the Arctic Ocean, which has low water temperature and low salinity, and is called a cold current. Another stream flows into the ocean from the coastal river. The water temperature changes with the atmospheric temperature, and the salinity is the lowest, which is called coastal water. Due to the force of various ocean currents and the north-south movement, the marine environment has changed. Every spring, the earth warms, the south wind blows frequently, the warm current in the ocean gradually strengthens northward and extends to the coast of China, while the cold current gradually weakens and retreats from the north, which makes the water temperature in the coast of China gradually increase from south to north. In this way, according to the water temperature, salinity, sediment, bait and physiological requirements, all kinds of fish that used to overwinter in the south and deep sea congregated from south to north and from deep sea to shallow sea to seek bait or spawn and migrate. At that time, fishermen sailed out to sea and chased hairtail, yellow croaker, pomfret, catfish, mackerel and squid in large numbers from south to north. In April, May and June every year, the fishing season is closed in spring and summer. This is "three days after spring, fish will go north".
After autumn every year, the cold air keeps going south, the north wind increases, the cold current in the ocean gradually goes south, the water temperature along the river entering the sea also decreases, the warm current is relatively weakened, and the seawater temperature gradually decreases from north to south. In this way, in order to get a suitable water temperature, the fish scattered for food after spawning gradually regroup and swim to the southern sea or deep sea, forming a wintering migration, that is, "the fish go south three days after autumn."