Learning how to read a sounder is less about memorising coloured shapes and more about understanding depth, bottom hardness, structure, bait and fish returns together. Andrew Hestelow built his approach around a Lowrance HDS sounder while fishing Sydney Harbour, Long Reef, Twelve Mile Reef and Brown's Mountain. His examples still make a useful foundation for reading a modern Lowrance fish finder.
- Start with the bottom: identify the depth, shape of the ground and transitions between hard structure and softer bottom.
- Learn what a bait school looks like on your own palette, then look for larger returns beside or beneath it.
- Do not expect every fish to draw a perfect arch; fish may appear as short marks, blobs or irregular returns depending on speed, beam angle and settings.
- Tune sensitivity/gain high enough to show useful detail without burying the screen in noise.
- Use colour as an indication of return strength on the chosen palette, not as a universal species label.
- Once you mark fish, put the bait or jig at that same depth rather than simply fishing the bottom.
What are you actually looking at on a fish finder?
A traditional 2D sounder sends sonar pulses through the transducer and displays the returning echoes as a scrolling history. Strong and weak returns are represented differently according to the unit's palette and settings. Your job is to combine those returns into a picture of the bottom, structure, bait and larger fish.
That is why a sounder should be interpreted rather than treated like a literal underwater photograph. Boat speed, drift, transducer beam, water depth, sensitivity, palette and the position of a fish within the beam all change the shape you see on screen.
1. Learn to read the bottom and structure first
Before trying to identify fish, learn what the ground looks like. Hard structure reflects a stronger signal than soft sand or mud, so changes in the thickness and colour intensity of the bottom return can reveal where one bottom type gives way to another.
Those transitions matter because structure concentrates life. Andrew's examples include tiny isolated objects on otherwise flat sand holding dense bait schools, the edge of Long Reef stacking bait and predators, and the Sydney Artificial Reef producing a distinct structure return surrounded by fish.
When you are learning, confirm what the sounder tells you against places you already understand. The more known reefs, sand flats, wrecks and drop-offs you view, the faster the screen stops looking like abstract colour.
2. Recognise bait schools
Bait does not always make one standard shape. Slow-moving species can bunch tightly around structure, while higher-energy bait such as slimy mackerel may appear briefly as the school moves through the beam.
Andrew's Middle Harbour examples show why that matters. At a tiny piece of structure on otherwise open sand, bait could pack directly over the mark. When a larger predator appeared under the school, the useful fishing information was not only “there is bait here” but also the predator's exact depth relative to it.
If you are catching live bait, match your rig to the depth on screen. Colour-change braid or a detachable line counter can help put a sabiki into the school instead of several metres above or below it.
3. What do fish look like on a Lowrance sounder?
Do not wait for textbook arches. Lowrance's current sonar guidance also notes that fish can show as distorted arches, compact marks or dense blobs because a perfect arch depends on how the fish passes through the transducer beam.
Andrew's older HDS-5x palette produced distinctive returns of its own. On his preferred setup, large kingfish could appear as irregular mid-water blobs while smaller bottom fish produced different coloured returns. Those exact colours should not be copied blindly to a different unit or palette; the valuable lesson is to learn the repeatable relationship between return strength, shape, position and the fish you actually catch.
What do kingfish look like on a sounder?
Kingfish commonly show as strong mid-water returns around bait or structure rather than being glued to the bottom. Andrew describes one Twelve Mile Reef session where a small group of strong marks appeared around 75–80 metres; the crew sent four jigs to that depth and boated four kingfish. That is exactly how a sounder becomes a fishing tool rather than just a depth display.
4. Tune sensitivity, colour and interference
Andrew deliberately adjusted gain and colour palette to make different returns easier to distinguish. The goal is not the prettiest screen. You want enough sensitivity to show weaker targets without creating so much clutter that useful marks disappear.
Interference matters as well. In his original Lowrance screenshots, another nearby sounder could produce broken vertical lines across the display. Aerated or turbulent water around the transducer also degraded the return, particularly in deep water.
Modern Lowrance units offer more automation than Andrew's HDS-5x. Lowrance's current guidance suggests starting with Auto and then making small sensitivity adjustments as needed. It also recommends comparing traditional 2D sonar with DownScan when structure makes individual fish difficult to separate.
Old screenshots, current principle: Andrew's examples were recorded on an older Lowrance HDS-5x. Current units have newer CHIRP, DownScan and SideScan capabilities, so menus and exact colours differ. The fundamentals—return strength, target separation, bait depth, structure and careful tuning—remain useful. For model-specific settings, use your unit's manual and Lowrance Australia's current sonar guidance.
5. Put your bait or jig where the fish are
A sounder becomes valuable when it changes what you do next. If bait is marking at 30 metres, fish 30 metres. If kingfish are holding around 80 metres over much deeper water, a jig sent to the bottom wastes time and may pass below the fish completely.
Andrew repeatedly used colour-change braid and line counters to turn a mark on screen into a repeatable fishing depth. The same idea applies whether you are catching live bait, jigging a reef edge or presenting a bait to suspended fish.
6. Reading a sounder in very deep water
Brown's Mountain was Andrew's extreme example. His HDS-5x could still mark bands of fish in more than 500 metres, although rough water and aeration around the transducer made bottom tracking more difficult. He used a slower ping speed and increased gain to pull useful detail from the depth.
Do not copy those historical settings as a preset for a modern unit. Deepwater performance depends heavily on transducer, frequency, installation and conditions. What the example proves is that the sounder can still guide your fishing even when the bottom trace itself is imperfect: fish marks at 150–250 metres and 450–500 metres told the crew where activity was occurring in the water column.
Lowrance sounder questions
How do you read a Lowrance fish finder?
Start by identifying the bottom and obvious structure, then look for bait schools and stronger fish returns around them. Learn how your chosen palette represents return strength and adjust sensitivity only enough to reveal useful detail. Finally, fish the exact depth where the marks appear.
Do fish always show as arches on a sounder?
No. Fish may appear as complete arches, partial arches, short marks or dense blobs depending on boat speed, fish movement, beam angle, scroll speed and sonar settings.
How can you tell hard bottom from soft bottom?
Hard bottom produces a stronger sonar return than soft sand or mud. On a traditional 2D palette this normally appears as a stronger, more intense bottom band. Learn the appearance by comparing known hard and soft areas on your own unit.
What do kingfish look like on a sounder?
Kingfish can show as strong mid-water marks, arches or irregular blobs, often around bait or reef structure. The exact colour depends on the palette. Andrew's key technique was to identify the depth of those marks and send jigs or baits straight to it.
Why are there vertical lines on my Lowrance sounder?
One possible cause is interference from another sounder or transducer operating nearby. Turbulence and aeration around the transducer can also degrade the image. If the pattern is persistent, check installation and your model's interference/noise settings.
Read Andrew's original depth-sounder article
The four-page Boat Mag feature is preserved as a PDF. The scans below are the original Lowrance examples that accompanied it.
View the original article PDF
