Sounder Basics: tips on how to read your “Fish Finder” (Words and Image by Nabeel Issa)

After a number of requests following his previous article, this week Nabeel goes ‘back to basics’ with sounders.

In the last article I wrote, I talked about the Insight Genesis mapping software available for Lowrance and Simrad users. This time, I have had a few requests to go back a bit and go over a few more basic things about reading sounders.

I’m sure we are all familiar with traditional sonar, most, if not all sounders will have this in some form or another. It shows us what is under the boat and in the beam of the transducer. Fish will generally show up as an “arch” shape when they pass through the beam.  I made up the below diagram to help explain this easier.

Diagram showing how fish arches are created

Diagram showing how fish arches are created

As the fish enters the beam (1) it is at a point that is furthest away from the transducer, so we get a small mark showing. Once it is in the centre of the beam (2) its closer to the transducer and we get a stronger return so we get a larger chunk. Lastly when it leaves the beam (3), it is further away so we get a weaker reading and a small mark. This is what gives the arch shape. So when you do see an arch, it’s safe to say that fish went directly through the transducer beam and would have been under the boat.

 'Traditional Sonar' screen shot with a number of Bass. Image courtesy of Lee Parkhouse

‘Traditional Sonar’ screen shot with a number of Bass. Image courtesy of Lee Parkhouse

The above image shows a few longer fish arches . The reason we aren’t seeing shorter more typical arches here is all to do with speed. If we were travelling very slowly the fish in our transducer beam would spend a greater amount of time in the beam and therefore show up as a longer arch. If we travelled faster over the same fish we would get a more condensed smaller arch. So it’s important to note that longer arches don’t always mean bigger fish!

Another common feature on most Lowrance sounders is called Down Scan. Most other brands will have a similar feature with a different name, and will work similarly. They are becoming more and more affordable and you can even find this feature on entry level units. I’m a big fan of using Down Scan over Traditional Sonar for the simple reason that it takes all of the guess work out of sounder reading.  Have a look at the below image. On the left we have a traditional sonar image and the right we have Down Scan.

shot 20 (2)

The left side shows us a few fish arches as well as a big clump of well… something. It’s hard to say exactly what but it looks like some sort of hard structure. The right is a Down Scan image and we can now start to get a better idea of what is happening.  It’s actually part of a wreck.  The advantage that the Down Scan image has is that we can see fish that are close in to the structure (inside and around), they don’t just get muddled up into the big clump of yellow like the image on the left. We are also getting a better image of the actual structure.

I often get asked what the best settings are for a sounder …and well to be honest. There is no perfect setting!  I can only speak for Lowrance sounders as that’s what I use, but 99% of the time I will leave mine on “Auto.” This will automatically adjust the settings such as range, depth, sensitivity and contrast to give you the ideal image. There are times when I will alter the contrast and range a fraction but it is generally only a small amount.  If you are only new to sounders then it is definitely a good idea to leave the settings on auto.

So there are just a couple of things I thought I would write about. In the future I will go into some more specifics such as selecting frequencies, transducer placement and how to read Side Scan (that almost needs an article on its own!) If anyone has anything in particular they would like covered just leave a comment and I will do my best to help!

Nabs (Nabs12), is a seasoned angler that fishes the Australian Bream tournament circuit.  He enjoys all aspects of fishing, in particular chasing Snapper and Jewfish in Moreton Bay.

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