As anglers we all face many of the same dilemmas, regardless of the style of fishing we choose. Bait fishing, trolling, coasting, spinning and fly fishing all rely on two main concerns; namely finding fish and getting them to bite. No matter what type of fishing you pursue, locating fish has got to be one of the most important facets of sport fishing. If you fish from a boat a depth sounder or sonar (short for Sound Navigation Ranging) is a vital piece of equipment. In addition to this equipment, the challenge of learning all one can about a fish species and catching their fish is an important factor in why many of us take up the sport. Rather than talk about choice of lure fly or bait I'd like to concentrate on locating fish including using sonar.

Each fish species reacts differently to their environment. As a result of both habitat and to some extent genetics, fish react to stimuli through their senses: sight, smell, taste, touch and hearing all play a part in how any fish species will react to your presentation. Locating fish also depends on a specific species need for food, comfort and the biological need for reproduction.

To satisfy their needs and instinct for survival different species of fish have different requirements or preferences for food. Factors such as temperature, weather conditions, time of year or season can all influence how fish will react in their chosen environment.  Spawning requirements vary considerably from one species to another, as each species is very different. Developing an understanding of different species is vital to becoming a successful angler. To catch fish consistently, targeting a specific species requires you treat each species differently and to fish for each species differently. In both salt and freshwater, structure plays a huge part in any species preferred habitat.

Fish located in dark stained water are generally more conscious of vibration due to the lack of visibility and usually rely on a mixture of sight, feel and hearing to locate their food.  While fish located in very clear waters are likely to be more sight oriented when it comes to chasing a meal. Pockets or areas of weed are always a good spot to target fish.  In most of our impoundments these areas can provide fish with yabbies, mudeyes, invertebrates and a host of other insect life. Areas such as river mouths or any area where water comes into or leaves a body of water has an impact on fish location.

Interaction or the relationship of how different species behave toward one another also has a big influence on fish location. Available food sources, fish numbers and competition between species play an important role in fish location. Some species of fish are compatible, while others are not. Available food sources determine growth rates of individual fish and the general health of a fish population. The survival of any fish population is also directly influenced by a range of outside influences. This can include factors like localised weather conditions, seasonal fluctuations in temperature and water levels as well as any intervention by human beings. Intervention by man in the form of boats, fishing pressure, pollution, swimming, artificial or other changes in habitat all affect fish location and ultimately, our fish catches.

Although some of the above mentioned conditions are beyond our control as anglers, many of these mysteries of underwater conditions can be unravelled with the help of modern sonar.  In the past few years the sophistication of electronics and computer technology has leapt ahead. The application of this technology to sonar and GPS has resulted in a real bonus for anglers. The latest generation of sonar can show you an entire new view of the underwater world! Over the years I've used a lot of different sounders, most of which performed admirably, but my new Lowrance LCX16 is one truly remarkable piece of equipment. The power and clarity of this unit has to be seen to be believed.


Locating fish and their food sources without the aid of sonar can be a tall order. Using the LCX15 for this task will allow you to target schools of baitfish and weed beds that are likely to hold food for a hungry predator. When searching likely locations for fish it pays to keep in the back of your mind that your looking for habitat that fish are comfortable in, but you also need to consider the environment for their prey or forage. Water temperature and clarity plays an important role in any fish behaviour or activity. The type of water you fish also has an affect on the operation of your sonar.  Sound waves from your sonar travel easily n clear fresh water.  Freshwater is affected by wind, currents, suspended particles, and micro-organisms that have an affect on the signal, but this is generally minimal.  In saltwater sound is absorbed and reflected by suspended material in the water and requires the use of lower frequencies to remain effective. The LCX16 has the ability to run dual frequencies, very handy if you fish in both fresh and saltwater.


Water temperature, both surface and at depth, play an important role in fish behaviour.  Preferred temperatures for any given species is always a good starting point to locate fish.  Keep in mind that each body of water or fishing location will be different when considering water temperature.

Water temperature has a direct influence on spawning fish but also plays a big role in the daily patterns of any fish species. As little as 2 degrees in temperature can often spell the difference between fish in the net and failure. With the numbers of temperature probes available today there is no season why every angler can't monitor temperatures at almost any depth.

The temperature in any lake or impoundment is rarely the same from the surface to the bottom. Reams of information have been published by many scientists about stratification, the layering of warm and cool water in lakes and impoundments. For anglers, the important part of this process is where the two layers meet, the thermocline.The depth and thickness of the thermocline can vary with the time of day, season, intensity of sunlight and wind or wave action. The thermocline is never an exact band, but rather one that is constantly changing in depth, intensity and size. In deep lakes the water may even stratify in to two distinct thermoclines. The band of water which forms the thermocline is important because many species of fish like to suspend in, just above or just below the thermocline. Have a look at Figure 2 which depicts an impoundment , in this case Moogerah Dam in South East Queensland, that clearly shows two distinct thermoclines. Many species of baitfish will suspend just above the thermocline with the larger predators in or slightly above it.  Monitoring the location of the thermocline is easy with the aid of sonar. The larger the temperature difference between the layers of water the more dense the thermocline shows on the screen.


Structure in any lake or body of water can encompass a range of factors. When referring to structure its necessary to consider the range of structures in a species environment.   Generally most anglers think of structure in terms of submerged trees, rocks, shipwrecks, etc. Structure also includes elements like bottom configuration, bottom contents, water movement, vegetation, drop offs, submerged points, water depth.  

When prospecting a new area or body of water, watch your sounder carefully. A great looking bit of fish holding structure near the bottom of a lake that stratifies in summer is likely to be a poor target area if its below the thermocline and has poor oxygen levels in summer. The depth of any structure will determine how fish use it.  Extensive weed beds in very shallow clear water are unlikely to be frequented by predators in intense summer daylight.  Any structure used by fish needs to be at a depth that is appropriate for a given species requirements. Bottom content including rock base, weed beds, boulders, sand or mud can all make a difference to your success. Don't waste your time pursuing an area that doesn't have the right bottom structure to attract the species your targeting. The sonar image in Figure 5 depicts a classic example of fish seeking structure.  Don't get caught in the trap that most anglers fall for, structure or the shape of an area alone doesn't attract fish.  The best fish attracting areas generally show a combination of structure, weed, depth and available food. Fish often make use of different areas according to the season or time of year. To be a really successful angler means not only using the right techniques and gear, but developing an understanding of fish species and their environment.