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Catching up with fish
What can we learn from this fish finder screen?
This screenshot was taken while the boat was stationary. On the left side of the fish finder image, you can see what captured echoes look like at 50 kHz and on the right side at 200 kHz.
The echo at the bottom of the screen, within 2 meters above the ground, is that of a school of Barracudas.
More precisely, after pulling the line, half of them were Red barracudas and the other half were Japanese barracudas.
The place where I would like to draw your attention on this screen is the line representing the bottom of the sea. Logically, if you place the boat in a specific location, stationary, then the seabed should remain flat on the screen.
This is because the ultrasonic waves are sent to a specific point and, since the boat does not move, the objects being reflected will stay the same as well.
*On a fish finder, the seabed is scanned vertically at regular intervals and As time passes, it is the echoes of these already scanned objects that are reflected on the screen. This is why, if the boat is stopped at a specific location, the scanned seabed will always be the same and therefore, the echo of the seabed displayed on the screen will form a straight line because it is invariant.
However, as you can see from the screenshot, the surface of the seabed is not flat but quite irregular.
In fact, at the time of the screenshot, there was swell that caused the boat to move up and down 1. 5meters. It was this swell that deformed the seabed on the screen.
Returning to the Barracudas, they were fished in about two minutes and the echo of their school disappeared immediately after fishing them. Barracudas are migratory fish, so this means that they do not stop at a given place but that they are rather passing through.
In order to find even more fish, the boat was moved to another location. and echoes similar to those we have already encountered appeared. Again, these were Barracudas whose echoes disappeared right after being captured and pulled out. Bad luck for them!
On the screen, you can also notice the presence of vertical lines crossing the screen. These are actually interferences caused by an ultrasonic wave machine installed on a nearby boat.
It is possible to easily suppress the noise of this interference using a suppression function on the device, but by doing so, you run the risk of significantly reducing the returning echo of Barracudas themselves. Therefore I had decided to disable the noise suppression function.
Japanese barracudas are seasonal fish because they are migratory so let's use the fish finder as best we can in this short timeframe.
DAIWA field tester, Writer at Boat Club, a monthly Japanese boating publication
Nobuaki is a hobby angler who travels around Japan together with his beloved car-top boat Tomoe-maru. With a keen interest in fishing as well as scuba diving, he has gained a substantial amount of knowledge in how to utilize fish finders to the fullest. Nobuaki regularly holds well-attended training courses in the use of fish finders, as well as being a proponent for proper sea manners and safety at sea. Sharing his knowledge is a passion for Nobuaki, and he manages his own homepage as well as being a sought after writer in Japanese boating publications.