It’s one thing to have a sounder or “fish-finder” on your boat – it’s another to know how to read it! Adam Clancey shares his take on understanding what’s on your screen…

One of the most common fishing questions I am asked is how to read sounders. I am no electronics wizard, but I do use marine electronics a lot, so it’s fair to say I am an experienced end-user. Unravelling what your screen is showing is quite straight forward once you have seen a few different scenarios. In time, you should be able to tell snapper from other fish and spot kingfish and kahawai.

The first thing that is important with any fish finder is the correct installation and set up. Personally, this is a job I leave to the experts, and unless you are skilled in that field, I would recommend you do the same. Transducer positioning can be a real problem and varies from boat to boat. You also need to make sure you get one with enough power to meet your needs. Most transducers perform well up to 100 metres, but if you are planning on some deepwater fishing, you will need to choose your transducer carefully.

All of us have heard the cry from one of our mates, “there’s sign on the sounder”, but then had no action at all. Firstly, fish finders don’t lie unless someone makes the rookie mistake of leaving the new unit on demo mode. I tend to leave fish alarms and the like off – I am more interested in the picture I am seeing. Your target or targets may vary from the traditional ‘arch’ to just a streak or even a massive blob of colour.

Classic arches usually mean good fish, and you can see there are small baitfish on the screen as well.

These targets can be made up of one or multiple species of fish and dependant on the depth and your settings, each may look very different. One thing most fish finders do is give a shadow that can fool you into thinking there is more sign than there actually is. At eight metres you can see individual mackerel, whereas at 40 metres this might look like a ball of bait due to the shadow and because the return from the pings your sounder sends take longer to return and fish are moving. If you have fish on the sounder that look like they’re a decent size and you are getting no bites, two things might be happening. The fish may not be able to be caught on rod and reel (a good example of this is the silver drummer which are common), or it may simply be that the fish aren’t feeding at that time. As you grow more accustomed to your sounder, you will be able to identify actively feeding fish by their movement or by their position in the water column.

When lure fishing, your sounder can be used to accurately position your lure among fish sign as you will often see a trail left by the lure as it rises and falls. Remember that you must have your lure in the cone of the transducer for this to work. Through practice, we are noticing fish coming and having a look at our lures more and more, and can even have a good idea of the species. For example, when I see a fish swimming up from the bottom, I know it is quite often a gurnard looking at a jig or flasher rig. One of the key things to look for is good separation of the sign from the bottom when fishing over reef. This is a sure-fire indicator you are seeing fish. When fishing livebaits – either trolling or dropping them down in deep water – you will often see when larger targets are approaching bait schools and also how actively they are moving. This will tell you whether they are hunting.

Baitfish being chased by kahawai and kingfish.

It can be a little frustrating when you get a constant mark at a certain depth or marks in mid-water that are hard to identify. Usually, there is a good reason for this. Changes in temperature at different depths can give you a false reading, and at other times large amounts of plankton or small animal life can be in the water. To avoid this, you can reduce your gain a little, so only more solid targets show up. The gain controls the sensitivity of the fish finder. Other problems can be interference from air bubbles, which can be caused by wake that has passed you, and electrical interference. If this is ongoing, try increasing your noise rejection. In most cases, auto gain and auto range work fine, but these are both worth adjusting if there are consistent issues.

There are other settings on my sounder I also make use of a lot. The A scope shows the strength of the actual echo by displaying its width and colour. Zooming in on an area of interest is a good way to see what is going on and identify targets, especially if you are only interested in the bottom half of the water column – e.g. when you are deep water fishing for tarakihi or hapuku.

The next time your mate comments there is sign on the sounder, take him at his word. Then you can focus on solving the next part of the puzzle: getting what you can see on the sounder to bite!