Winter is here and once again anglers from Copenhagen discuss if the cod are staying in the harbour or moves out to deeper water. Ewout Mannes is not much into discussions without data, so he bought a “Deeper” which is a castable sonar, that can show you how many fish are beneath it and what depth they are in. It can also give you an indication of their size. I really look forward to follow his findings in the future. Read his first test results from a bassin in Nordhavn here.
What is a Deeper?
A Deeper is the perfect way for streetfishermen to find out if there are fish in the area and what the bottom looks like. Using an underwater camera or doing some scuba diving is not optimal in 5 degrees celsius in the harbour, so I went online and did some research if there were any other options. Then I found a company called Deeper. They make a small castable sonar that connects trough Wi-Fi or Bluetooth to a phone / tablet. After some searching I found a good deal and bought a Deeper Pro Plus with a night vision cap. If there are any others that want to know how the Deeper works you can follow this link: https://deepersonar.com/uk/en_gb/how-it-works/how-sonars-work
What did it show when you used it in Nordhavn?
Ok, so the location we went to fish was 10,3 meters deep. This image below is from the Deeper when I am reeling it in. So it’s moving on the surface and the fish are moving under it. On the right hand side you see the depth in meters. At number 1 you can see there is a cluster of fish on the 2,7 meter mark, these are probably some smaller group fish. Because there is a lot of small sonar hits and the fish are moving in a pack. Number 2 shows a fish on the 5,5 meter mark. This is a bigger fish because the sonar hit is a thicker mark. Right after you see a fish moving to deeper water. Number 3 shows 6 fishes that are hanging around the bottom.
The image below was taken when the Deeper was stationary on the surface and moving very slowly in the current of the waves. At number 1 there is a fish that is just hanging on the same spot and creates a long line on the screen. This on a depth of 6 meters. Right under this fish is another fish that is moving to deeper water. Going from 6 meters to 10 meters. Number 2 shows a fish that is slowly rising from 3 meters to 2,7 meter. Number 3 shows a fish / fishes that are on the bottom of the bassin.
So I can easily conclude there is still fish on this spot and some of them are of a good size.
For the more technical minded can you explain more about how the sonar works?
The Deeper Pro Plus has a built-in GPS and it can send a wide beam (55°) or narrow beam (15°) at 15 pulses per second. The maximum depth it can detect is 80 meters. The built-in GPS makes it possible to make underwater maps from the area you want to look at. These maps are saved in your Lakebook, which is an online map that you can use for choosing where to fish.
The beam makes a cone through the water it is moving over. Wide beam scanning is good for quickly scanning large areas and getting overall information on depth and bottom structure, but the accuracy and detail will be lower. I made a comparison of the beam diameters on the bottom. The depth of the water is 10,3 meters in this comparison.
So the images on the screen of the phone / tablet are from a cone with a diameter of 10,7 meter on the bottom when a wide beam is used and 2,7 meter on the bottom when a narrow beam is used.
The images are scrolling on screen because the Deeper sends new information all the time. Fish are shown as lines or arcs of yellow/green color. You’ll only get arches from moving fish (or if your sonar is moving over them). If your sonar and the fish are both stationary, you will see a line instead of an arch. You’ll only get a full arch if the fish moves through the full sonar cone. If a fish swims through part of your cone, it will show as a half-arch or a thick dash. The pictures here are made with wide beam and the lines and arches you see are the fish.
What do you plan to explore with your Deeper in the near future?
I am planning to go to some more bassins and check out the depth and objects that could be there. Of course I will also be looking if there is any fish there. Another idea is to go to some lakes and test it in freshwater with sloping banks. If anyone has any other good ideas or questions please write a comment down below.