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Catching up with fish


What can we learn from this fish finder screen?

Greenling By comparing the fish-finder screen with the GPS chart’s contour (bathymetry) lines, it is much easier to imagine the seabed structure and landscape.

The above screenshot was taken with the boat moving at a slow speed (0.5 kn) and the fish finder was set to transmit at 200 kHz, with bottom zoom enabled.

Fish finder screen explained

  • Water depth: 19 m
  • The seabed shows a height difference of 10 meters.
  • Seabed composition: Sandy/muddy to rocky
  • You can see single fish, sized at approximately 10 cm, just above the peaks in the seabed.
  • Water depth changes drastically (very quickly) according to the GPS chart

The tackle used was Tenya, a sinker+hook combination, used mainly in Japan, with a spinning reel. A Tairaba rubber jig was also used and the combination was enough to attract and catch Greenlings.

Greenlings favor coastal reefs and wrecks, covered heavily in seaweed, at depths between 5 meters and 50 meters.

Let’s have a closer look at the GPS chart. When the depth change is not large, the distance between contour lines is wider. You can see that the depth around the boat (indicated by the ship icon) changes abruptly, as indicated by the contour lines. The depth change is also shown on the fish finder screen as the trough between the two peaks.

Now, let’s compare the seabed, as shown on the fish finder, with the GPS chart’s depth data. The fish finder shows the latest data on the right of the screen and scrolls to the left as time goes by.

The oldest data on the screen is shown on left-hand side, with a rocky seabed and shallow depth. The latest data is shown on the right-hand side, with a rocky seabed and moderate depth.

The seabed composition around the example area is a mix of mud and sand, with a depth of 25 meters.

A GP-1870F with chart functionality can help you anticipate seabed composition thanks to its detailed contour line and depth information.

When looking for Greenlings in their natural habitats, it’s recommended that you use a GPS chart to help anticipate abrupt depth changes and avoid snagging your nets or lines.

  • Greenling The better types of Greenlings are often likened to beer bottles; well-shaped with a good size and coloration, which is a rather accurate analogy.
  • Greenling It’s recommended that you use a GPS chart to help anticipate abrupt depth changes and avoid snagging your nets or lines.

Writer introduction

Nobuaki Ono, FURUNO field tester.

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.