Among the expressions used by anglers, there is one called feeding time. Its original meaning is the time when babies are fed or animals are fed, but it is also used to refer to the time when fish are actively feeding, that is, the time when they are actively biting.
And the time when fish are most active in biting is often said to be just before sunrise and sunset. The most important reason is, as discussed in the article “Why shouldn’t you shine a headlamp on the water?”, among the plankton in the sea, phytoplankton start to move for photosynthesis just before the sun rises, and nocturnal zooplankton start to move actively just before the sun sets. Fish also increase their feeding activity to eat these plankton, which is why it is said that early morning fishing is good.
However, this is not the only reason why the fishing is good. The better the conditions are, the better the fishing is. Today, among the various factors that affect the fishing, let’s find out how the ecology of fish changes just before sunrise and sunset.
Let’s learn about the times when fish are most active in biting, based on a 1994 paper (Effect of Diurnal Activity of Rainbow Trout and Light Intensity on Gillnet Catching in Water Tank Experiments) that not only do the times when plankton are most active coincide with the times when fish are most active in moving, but also that fish are less alert during those times.
The purpose of the study on rainbow trout was to determine when they were most active and to determine the correlation between ambient brightness and entanglement in nets, and the paper contains information that is also very useful for anglers.
According to the research results, rainbow trout were more active during the day, showing high activity in the morning and evening when day and night change, and while activity decreased at night, activity increased sharply just before sunrise.
If we look a little more closely at the movements of rainbow trout in response to light in nature, we can see that they show more active movements just before the surroundings become dark or bright, which means that the fish become more active just before sunrise.
This is because, just like humans, fish also have various reactions that occur in a 24-hour cycle. This is similar to why we feel sleepy at night even when we are under bright lights, and why we wake up in the morning even when the darkness persists with the curtains drawn.
Meanwhile, the researchers who participated in the experiment released 50 rainbow trout into a tank 4 meters wide and 1 meter deep, then installed a gill net in the middle of the tank and observed how the number of fish caught in the net changed depending on the lighting.
As a result, rainbow trout became more active as the light grew brighter, while the number caught in nets decreased. This means that the darker the surroundings, the higher the rate of trout caught in nets. This result shows that the thickness and color of the leader do not significantly affect the catch in night fishing.
The relationship between rainbow trout activity, net catching rate, and lighting is shown in the figures below. From these figures, we can see that the number of trout caught in the net is high just before sunrise and just before sunset, and during the daytime when they are active. This clearly shows that it is difficult for fish to notice fishing gear just before sunrise and sunset. Soldiers on guard duty in the military are familiar with the period from Begin Morning Nautical Twilight (BMNT) to End Evening Nautical Twilight (EENT), which makes it difficult to distinguish the outlines of objects with the naked eye. Therefore, various nighttime military operations such as ambushes and guard duty begin around BMNT and end around EENT the next day. This also applies to fish.
Changes in light brightness according to time of day
Changes in rainbow trout activity over time
If we combine the two pictures above, we get the following:
Figures 7 and 10 in the paper show the correlation between the activity of rainbow trout and the number of fish caught in nets according to the brightness of the surroundings. They clearly show an inverse relationship in which, as the brightness increases, the movement becomes more active, while the number of fish caught in the net decreases.
People who enjoy night fishing often miss the feeding time just before sunrise because they are tired. However, this experiment clearly shows that you must not miss this time and concentrate on it as the movement of plankton and baitfish, which are the prey, becomes more active and the activity of the target fish also increases.
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