1. Kuroshio Current

When fishing in the marine environment, we must naturally consider the changes in ocean currents, and the ocean current that has the greatest impact on us is the Kuroshio Current.

Ocean currents are a form of seawater flow. They are wide-ranging and stable in nature, and will have a significant impact on the environment, climate, ecology and even culture of the area they pass through.

Why does seawater flow? There are several reasons:

(1) Wind influence. The earth’s surface has a roughly fixed planetary wind system (surface wind system with a global impact range) and relatively unstable, localized aeration disturbances (such as typhoons). When wind of a certain direction and intensity blows over the sea surface for a period of time, due to the effect of friction, the surface of the seawater will flow in the direction of the wind, and the flow of water molecules on the surface will drive the water molecules in the lower layer to move with it (but the speed will gradually decrease), thus generating water flow. This is called “blowing current”.

(2) Differences in seawater density. The salinity and temperature of different parts of the ocean are not equal and constant. These differences will cause different densities of water masses. High-density seawater is heavier and low-density seawater is lighter, so it will cause the seawater to flow. This phenomenon is called “density tide”.

(3) Tidal rise and fall. Under the influence of the gravity of the sun and the moon, the seawater will rise and fall periodically. The water flow caused by this rise and fall of the water level is called tidal current.

(4) Compensatory effect. Seawater is a fluid, and fluids are continuous. Therefore, when the seawater in one place flows to another place, the surrounding seawater will flow to make up for the shortfall, which creates a compensatory flow.

So what is the Kuroshio Current?

The Kuroshio Current is a powerful current. It is part of the North Pacific Ocean Current System. It is formed because the surface seawater near the equator is blown by the northeast trade winds (a member of the planetary wind system) all year round. At the same time, the centrifugal force (Coriolis force) of the earth’s rotation forms the “North Equatorial Current” that flows from east to west on the north side of the equator. When this ocean current reaches the east coast of the Asian continent, it is blocked. Part of it turns back to form the equatorial countercurrent, and part of it turns northward and moves along Taiwan Island and the Japanese Islands. This part is the well-known Kuroshio.

After reaching northern Japan, the Kuroshio is blown by the westerly wind (also a member of the planetary wind system) and turns eastward. At this time, it is called the North Pacific Current. When the North Pacific Current reaches the west coast of the North American continent, one stream turns north and becomes the Alaska Current, and the other stream flows south along the west coast of the United States and becomes the California Current. This current will eventually return to the North Equatorial Current.

The Kuroshio comes from the equator, and its temperature is relatively high (the surface water temperature can reach 30℃ in summer and is not lower than 20℃ in winter.) Therefore, it is called a “warm current”. It can bring warm and humid climate to the areas it flows through, and also carries a large number of migratory fish (such as the bluefin tuna that appears in the waters east of Taiwan between spring and summer every year). During the flow, the “upwelling current” caused by the influence of topography or compensation will also bring nutrients from the seabed to the upper waters, attracting a large number of various organisms to gather, thus making the fish catch rich.

2. Causes and effects of tides

Experienced anglers often say that they should watch the “flowing water” before going out to cast their rods. This flowing water refers to the tides.

Everyone knows that the tidal phenomenon is caused by the gravitational force of the moon and the sun, but why are there high tides and low tides? Why are there two high and low tides every day? What is high tide?

(1) The so-called “tide”. The ancients called the rise and fall of sea water during the day “tide” and the rise and fall of sea water at night “tide”, and the two were collectively called tides.

(2) The rise and fall of tides. The process of sea water rising from a lower water level to a higher water level is called high tide, and the process of falling from a higher water level to a lower water level is called low tide. When the water level rises to the highest point, it is called high tide, and when it falls to the lowest point, it is called low tide. In addition, when the water level reaches the full tide or low tide point, there is usually a period of time when the sea level does not rise or fall. This is called a slack tide or a flat tide.

(3) The height of the tide. The height of the water level is not exactly the same in different places at the same tide, and the height of the tide in the same place on different days will also change.

The difference in water level on different days is mainly caused by the different relative positions of the moon, the sun and the earth. On the lunar new moon or full moon (new moon or full moon), the moon, the sun and the earth are roughly aligned in a straight line. At this time, the moon and the sun are on the same side or opposite sides of the earth. Due to the effect of gravity, the temperature difference between the full tide and the low tide is the largest. This is called a “high tide”. (But in fact, it will be delayed for two or three days). When the waxing moon or the waning moon (the seventh, eighth, twenty-second and twenty-third day of the lunar calendar) is seen, the moon, the sun and the earth are roughly aligned in a right triangle. At this time, the difference between the full tide and the low tide is the smallest, which is a “neap tide”.

The difference between the high tide and low tide is called the tidal range. The high tide range at the same location also changes periodically, from small to large, and then from large to small. The distance between the highest tide level and the lowest tide level is called the intertidal zone.

(4) Tidal cycle. The time of high tide and low tide varies from day to day. The interval between two high tides or two low tides in the same place is about 12:25. In other words, it takes about 6 hours for the tide to rise from low tide to high tide (and vice versa). The delay of the tide two days before and after will be about 50 minutes. This is called the tidal delay rate.

(5) Tidal form. Two high tides and two low tides every day are called semi-diurnal tides. Only one high tide and one low tide every day are called diurnal tides. If the actual tidal phenomenon in an area is not simply a semi-diurnal tide or a diurnal tide, it is called a mixed tide.

When the diurnal tide is more obvious, the time from high tide to low tide or from low tide to high tide will be much longer than 6 hours in a day. This is commonly known as “long tide”.

(6) So what impact does the tidal phenomenon have on fishing activities?

① Although the rise and fall of the tide is the vertical rise and fall of the sea surface, the interaction of factors such as topography, sea breeze, earth’s rotation, and gravity will cause the horizontal movement of seawater. In other words, it will cause ocean currents, which are an important way to transport food. When the water flows downstream during the low tide stage, food will not be transported to various places. Fish have lived in the ocean for a long time and are accustomed to adjusting their work and rest according to the water flow, so they often stop eating automatically during this period.

② When the tide changes, the direction of the current often changes as well, which means that the place where food is transported also changes, so the fish will of course move with it.

③ The seabed topography of the rock fishing site changes greatly. Since the direction of the current has changed, the punctuation is completely different. Therefore, if the angler does not have a full understanding and grasp of the tide, the results will inevitably not be ideal.

3. Coastal currents

In addition to the Kuroshio current and tidal phenomena, the flow of seawater in coastal waters is also of great significance to fishing.

When the flowing seawater comes into contact with the land environment and the seabed, many changes that have a significant impact on fishing will occur. These changes can be called the following according to the names used by the fishing circle:

(1) Main current. The so-called “main current” is not a specific name for a certain type of flowing water, but a relatively strong, fast, and main stream in an area. Usually, the direction is fixed (meaning that the direction is fixed during the high tide stage or the low tide process, but the direction may change after the tide changes.) and the flow rate is significantly higher than other surrounding water flows, which is called the main current.

In this kind of flowing water, it is more difficult for float anglers to maintain a fixed position or fishing platform depth. In some waters with particularly turbulent water, even if they use dinosaur eggs or high-load long floats, they will be quickly carried away. Anglers often call this kind of flow condition “flow ditch”. However, not all fishing grounds have main currents. In some places, the dynamics of the seawater are relatively slow or turbulent, so anglers will not define one of the currents as the main current.

(2) Tributaries. The word “tributary” is not a special term, but a relatively small area of ​​water flow with a slow flow rate and more variable direction compared to the main current. Such water flows may be pushed along the coast, or rush toward the coast or flow outward. Tributaries are not necessarily branches of the main current. Their formation is also affected by factors such as wind, waves, and tidal phenomena, and their direction, speed, and scale may change due to the influence of coastal topography and seabed conditions.

(3) Backflow zone. If the moving water flow encounters a change in topography (such as an inner bay or a convex headland) or a change in the depth of the sea area (such as a reef or a deep ditch), it is easy to form a surging and swirling water mass in this water area. This is the “backflow zone”. The size of the backflow zone will change with the water flow. The faster the water flow, the wider the range of the backflow zone and the more obvious its shape. The slower the water flow, the weaker the backflow zone may be. Backwash zones are particularly prone to trapping floating food in the sea.

(4) Backwash tide. Waves rushing toward the shore carry large amounts of seawater onto the rocks, and then turn over and pour back into the sea. This water must have a path to flow out. The seawater that flows out along this path is called a “backwash tide.” Its direction is always from the shore to the open sea, and it can wash organic matter on the shore into the sea and carry it out, so it has a strong charm to attract coastal fish. The method of finding a backwash tide is very simple. Just pay attention to the white foam caused by the breaking waves. If the white foam forms a line of white foam that continues to drag out for a considerable distance, that’s it!

(5) Tide eye. The so-called “tide eye” is when two (or more) streams of water with different directions or flow rates intersect, collide, and rub against each other, thus creating a water area with a relatively flat surface and no waves, seemingly little flow, and debris that easily stagnates. This water area is like a crossroads in the ocean, where fish and food meet and gather, so it is often used as a punctuation point for fishing.

1. Topography

There are two main factors that affect fishing activities in coastal waters: the curvature and convexity of the coastline, and the change in water depth.

(1) Coastline. A monotonous and straight coastline often lacks changes in the underwater environment (the beach is a typical example). At the same time, the direction of the water flow in this type of water area is mostly parallel to the coast, the flow rate is stable, and there is no food gathering here, so fish will not gather here. In an environment with obvious tortuous and convex environments, because the changes in water flow and waves are very rich, it is easy to form backflow zones, backwash tides, tide eyes and other conditions that attract fish, so the possibility of a good harvest is obviously higher than in a monotonous and straight area.

(2) Depth changes. The depth of the sea area not only affects the fish’s ability to adapt to water pressure, but also has a significant impact on the temperature, water color, salinity, transparency, water flow direction, speed, etc., so it will also affect the fish’s habitat and activity.

For example, a flat surface with no uneven rock layers, whether its slope is gentle or steep, or even extends underwater like a fault, will not easily attract fish to stay. However, if there are depressions, valleys or ridges in this flat bottom area, then the valleys and the base of the ridges will become the favorite habitats of bottom-living fish, and the ridges are likely to cause the ocean currents to surge, bringing food from the deep to the shallows, so the top of the ridges often become the gathering places for surface-living fish.

2. Bottom quality

For fishing, the relationship between the ocean bottom quality and the fish living there is of great significance in two aspects, namely, habitat and reproductive behavior.

(1) Habitat. Some fish will never come into contact with the seabed throughout their lives because their food is also active in the upper layers of the ocean. These fish are usually called offshore or surface migratory fish. However, the targets of rock fishing are mostly not these fish, but species that live close to or even directly on the seabed. Some of these fish species simply lie on the seafloor, such as flatfish and rays; some like to hide in crevices, such as groupers and morays; some are used to wandering around during the day and finding a cave to sleep at night, such as parrotfish. But more fish species use this kind of changing bottom environment as their habitat. When it is safe, they run out to enjoy the abundant food nearby, and when they encounter danger, they quickly hide in the barrier.

However, among the above fish, each fish still has different choices for the environment (bottom). For example, black porgy likes to live in mixed reef and sand areas, gar prefers gravel terrain, and black hair tends to gather in pure rocky reef areas.

(2) Reproductive behavior. Most fish are oviparous, but there are also viviparous or ovoviviparous ones between oviparous and viviparous. Regardless of their reproductive method, choosing an environment suitable for reproduction generally requires considering nutritional supplements before mating, the environment required for the growth of eggs or fry, and the physical recovery of the parents after reproduction.

Fish eggs are classified into floating, sinking and sticky types. Floating eggs need proper water flow to guide them to a suitable place for the young fish to grow and eat. Sinking eggs need enough small gaps on the seabed (such as gravel terrain) for them to settle, and the landing must be stable and have smooth water flow, otherwise the eggs will be washed away or rot. Sticky eggs need a more stable environment with smooth water flow, and must be sufficiently concealed, otherwise the eggs will be eaten up by other fish soon!

As for the tonic before and after mating, it goes without saying that it is directly related to the abundance of food, and a large part of the food source of the target fish species of rock fishing is directly attached to the bottom, such as algae, crustaceans, shellfish, etc., so the impact of the bottom is very significant.

Attempts on wind

The East Asia-Pacific region is a region with changeable weather. From the perspective of Taiwan, the weather changes periodically every year: After about March, the sun’s direct position extends northward from the equator, causing the Siberian cold high pressure on the northern continent to weaken, while the Pacific high pressure gradually develops. Therefore, the northeast monsoon gradually weakens and the southwest wind begins to replace it. In May and June, the ocean and continental air masses push each other, forming a stagnant front near Taiwan, causing the so-called plum rain season. In July and August, the strength of the Pacific high pressure reaches its peak, and the Taiwan region is dominated by southwest and southerly winds. However, during this period, tropical depressions are likely to occur on the ocean due to the evaporation of a large amount of water vapor. When the intensity of this depression reaches a certain level, a typhoon is formed. Therefore, after July, August, September, and October, the sun’s direct position moves southward, crossing the equator into the southern hemisphere, causing the Pacific high pressure to gradually weaken and retreat eastward, and the northern continental cold high pressure regains its advantage, causing the northeast monsoon to begin to move southward and dominate the weather in this area from December to February of the following year.

Based on the above rules, we can know that the wind or weather systems that affect the East Asia-Pacific region are mainly the following:

(1) Northeast monsoon. It is basically from the Siberian continent. It is cold and dry. The water vapor and ice crystals it contains exist in the high altitude. However, when it moves eastward out to the sea, it will be heated and absorb water vapor along the way. Therefore, the weather will become cloudy, windy, and rainy. A strong cold front will be formed at its leading edge.

(2) Plum rain front. The Plum rain front is formed by the mutual push of the Pacific warm air mass and the continental cold air mass. Because of the violent disturbance and the large amount of water vapor, it often causes obvious wind changes and rainfall. When the Pacific high pressure is strong, the stagnant front will be pushed northwest, and Taiwan will be covered by the marine air mass. The weather will be relatively clear and hot. If the continental cold high pressure is strong, the stagnant front will move southeast, and the weather in Taiwan will become cloudy and rainy.

(3) Typhoon. The harm of typhoons is self-evident, but there are three side effects that are often overlooked that must be mentioned, namely southwesterly airflow, long waves and storm surges.

Southwesterly airflow is different from southwesterly monsoon. Monsoon refers to wind that blows continuously for a long time and over a large area, while airflow is a climate phenomenon that is stationary and has large changes. When a typhoon passes through Taiwan, it will introduce strong southwesterly airflow due to its counterclockwise rotation. This airflow from the South China Sea carries a lot of water vapor, so it often causes serious disasters.

Long waves are waves with very long wavelengths, often caused by the strong wind and low pressure of a typhoon. They can spread to a very far place and move much faster than the typhoon itself. Therefore, they pose a great threat to the safety of anglers.

Storm surges are another big problem caused by typhoons. Their cause is similar to what was mentioned in the previous paragraph. Because the air pressure in the center of the typhoon is very low, the sea water will be sucked up and the sea level will rise. In addition, the strong wind will cause the sea water to rise even higher due to accumulation. If there is a high tide at this time, it will cause seawater backflow disasters to coastal areas.

(4) Southwesterly monsoon. In the east coast of the Asian continent and the waters on the west side of the Pacific Ocean, if there is no typhoon or tropical depression in summer, the weather is usually sunny and hot with weak southwest wind. The influence of this monsoon is not very obvious at first glance, but because the sun continues to add to the surface and there is a lack of wind to regulate, strong updrafts are generated near the surface, which often quickly develop into a huge cloud column thousands or even tens of thousands of meters high and anvil-shaped at the top. This kind of cumulonimbus cloud with a lot of water vapor inside will form a rapid and heavy thunderstorm after being cooled at high altitude. Moreover, this kind of rainfall can cause strong wind changes and form gusts of more than level 8 or 9 because it rushes down with cold air.

Common sense about waves

Waves are the oscillation phenomenon formed by seawater under the action of external forces. The most obvious and common cause is wind. But there are many other external forces that can also cause waves, such as crustal movement, submarine volcanic eruptions, tides, etc.

Although waves will spread outward from the place where they occur, water molecules do not move away with the transmission of waves. They only move up and down in the original place. Another special phenomenon of waves is that the depth of their impact is approximately equivalent to half of their wavelength, that is, if a wave with a crest-to-crest distance of 10 meters occurs somewhere, then its dynamics cannot be felt at a depth of more than 5 meters.

The above is a brief description of the general nature of waves. Do anglers still remember the “long waves” mentioned in the previous section? The so-called long waves are waves that come from distant seas and have been separated from their origin (for example, caused by a distant typhoon). This kind of wave has a very long wavelength, looks smooth and gentle, and has a low wave crest, so people often ignore its danger or are not easy to detect its arrival, but the energy it contains is extremely considerable, and it does not decay much during the journey, so it can affect far away places.

When this long wave advances to the vicinity of land, because the depth of the sea area becomes shallower, the kinetic energy stored in the wave begins to transform into potential energy, shortening the wavelength and increasing the amplitude, that is, the seawater appears to “stack upward”; the shallower the water depth, the higher the stacking height, and at the same time, because of the hysteresis of the seabed friction, the wave transmission speed in the deep is slower than that on the surface, so the wave shape also becomes forward-leaning, and finally the wave crest can no longer maintain a stable state and collapses, and a large amount of seawater suddenly hits the shore wall.

If this phenomenon occurs on a steep, deep rocky coast or the front end of a breakwater, because the depth is rapidly shallowing in a short distance, the wave crest may stack up to a level higher than people’s foothold in the blink of an eye, and the waves carry a large amount of kinetic energy and potential energy that have not yet been released, and all of them are loaded onto the anglers who are unable to escape, so the angler falls into the sea!

Wind speed and wave height correspondence table

In sand dune areas with gentle depth changes, the impact of general long waves will not be very serious, but if the incoming waves are caused by strong undersea earthquakes, then it may cause damage like the South Asian tsunami on December 26, 2004!