Fishing and Moon Phase


Most anglers will agree that water current is one of the most important deciding factors that affect the amount of catch especially when fishing in the sea, estuaries or large lakes. First of all current help to present the bait to the fish at the correct position in the water rather than lying on the sea bed or entangled to the main fishing line. Secondly, water current help to deliver the scent of the bait to the fish. Scent coming from the upstream bait will draw the fish out of the cover toward the source of the attractant. And third, water current move the plankton. Plankton attracts the small baitfish, which will attract the predator fish. For the predator fish, current simply mean it is time to hunt.

Too much current on the other hand is also not good for fishing. The sink weight will not be able hold the bait at the intended position. By increasing the weight we can hold it down but will potentially not be able to feel bites. Bait scent will be too dispersed and the fishes will move away to lower current area or into hiding. The debris caused by too much current will also affect the visibility of the fishes.

Hence, we need just the right water current to fish. For example, if we are fishing bottom fishes, we want the current to be moderate, not too slack and not too strong. So we should avoid both the neap tide and spring tide. If we are fishing for mid to top water predators, we want the current to be high and we should choose a day which is closer to the spring tide. If we are fishing in a river close to the estuaries with the presence of the preexisting current from the flow of the river, we will want to fish on the days close to the neap tide.

So what are neap tide and spring tide, and what is the connection with current? The movement of water brought about by the tides can be separated to the vertical and horizontal movements. The vertical movement is called the tide and the horizontal movement the tidal current. When the tide is rising and the flow of the current is directed towards the high tide, the horizontal tidal current is called the flood current. When the tide is receding it is called the ebb current. Between flood and ebb are slack water periods where there are little or no horizontal movement.

Tide is brought about by the Earth’s rotation, and attraction of the sun and the orbiting moon on the waters of the oceans. Although the sun and moon both exert gravitational force on the Earth, the moon’s pull is stronger because the moon is much closer to the Earth. When an area covered by the ocean faces the moon, the moon’s gravitational force on the water causes a high tide. At the same time on the area at the opposite side of the planet, the centrifugal force created by the Moon orbit pulls the ocean water out and causes another high tide at the opposite side of the Earth. As the Earth rotates, these area moves away from the moon’s influence and the tide goes down.

The vertical difference between high and low tide is called the tidal range. Although the sun is almost 390 times farther away from the Earth than is the moon, its high mass still affects the tides. The force due to the Sun is 0.46 that of the moon. When the sun, moon and Earth are all lined up, the sun reinforces the pulls of the moon. The combined pulls cause the highest and lowest tides, called spring tides. Spring tides happen whenever there is a dark moon or a full moon. When the moon is between Earth and the sun, it is in the sun’s shadow and appears dark. This is the dark moon. When Earth is between the sun and the moon, the moon reflects sunlight. This is the full moon. The current is stronger due to the higher tidal range. Spring tides are particularly large close to the equinoxes (21 March and 21 September) when the Sun is overhead at the equator.

In the period between the two spring tides, the moon faces the Earth at a right angle to the sun. This is the first quarter and last quarter moon. When this happens, the pull of the sun weaken the moon pull. This causes tides that are lower than usual. These tides are known as neap tides. The current is weaker due to the smaller tidal range. It takes the moon about 29.5 days to complete its orbit around the earth. This period is called a lunar month. So if the first day of the lunar calendar is a dark moon (spring tide), the 8th day will experience a neap tide and 15th a full moon (spring tide again).

Because the moon progresses about 12 degrees in its orbit around the earth during each 24 hour period, and because it orbits in the same direction as Earth rotates, the moon will not be directly overhead the area again until 24 hours, 50 minutes and 28 seconds. This is called a lunar day.

This number is important in fishing because we can make a good prediction of tomorrow from the active fish bite time today. For example, if the active bite time at a spot starts at 4pm today, we can predict that tomorrow active bite time at the same spot will starts at about 5pm.

In a lunar day there is supposed to be two high tide and 2 low tides that are more or less the same height (known as semidiurnal tides) but this is not true in every location because of land obstruction. Some locations experience one tide at one height and the second at a different height (mixed semidiurnal tides), and some locations have so much interference from land that they only experience one high tide and one low tide per day (diurnal tides). Shores around coastal islands and inlets where the water must funnel in through constrained waterways may experience delayed tides compared to open coasts.

Water current is also driven by several other factors. The depth of the water in the location determines how strong the current changes with the tides. In the deep ocean the current has little speed change but close to coast the current is much stronger.

Storm surge resulting from an intense storm also includes the rise in water level due to atmospheric pressure reduction as well as that due to wind stress. A storm surge occurs in conjunction with a high tide during spring tide can cause very high current.

Actual water current can also deviate from the tide prediction due to weather conditions. Winds drive currents that are at or near the ocean's surface. Another factor that drives currents is thermohaline circulation, a process driven by density differences in water due to temperature and salinity in different parts of the ocean. The current caused by thermohaline circulation move much slower than the tidal or surface currents.

In conclusion, here is no hard and universal rule that you have to fish during spring, descending, neap or rising tide. As an angler, we have to have some understanding of the tide current relationship and weather of the location we are fishing. You can use online tide charts, weather apps, specialized fishing apps or the simple tide chart above derived from the Chinese lunar calendar to find the favorable date.