Seeing Blind

An introduction to Sonar

30 Dec Seeing Blind

One of the most challenging things about fishing is knowing where to cast. Understanding fish location is crucial to maximize your chances of having a successful day on the water. Where fish hang out is generally dictated by a few common variables whether you fish rivers, lakes, ponds or the ocean. Northern Pike


All fish are opportunistic feeders. They eat when they can.  Many actively hunt down their meal and many use their environment to “lay in wait” looking to ambush their prey. Food is the single most important variable in a fish’s life.


Most fish are not able to regulate their body temperatures – they are cold blooded which means water temperature directly affects their metabolism. Depending on the species, there is an ideal temperature range for that fish.  Fish will actively move to find that optimal temperature. Depth: Many species of fish require a certain depth to be most comfortable depending on the season and their mating cycles.  Fish will constantly be on the move exploring different depths, often to regulate temperature or to hunt for food


Most fish feel comfortable around some sort of structure.  It could be a  rock pile, felled tree, floating object or even a dropoff or a submerged cliff.  Often baitfish will seek shelter in a type of structure which in turn will attract bigger fish as well, hence the start of the food chain.


Bass UnderwaterLike humans, fish need oxygen to survive.  Higher oxygenation levels are often found at creek or river-mouths and submerged springs.  Fish will naturally gravitate to highly oxygenated areas vs. “dead zones” where oxygen is low. So how do you know where to look to find these vital factors in fishing? It’s difficult to see submerged structure. Sometimes its impossible to test depth or temperature and baitfish are always moving.  Anglers rely on a piece of technology called sonar to give them the information they need to make wise, logical informed fishing decisions.  Sonar (SOund Navigation And Ranging) will show anglers food sources (baitfish) surface temperature, depth variation, bottom composition and submerged structure.

But how does it work?

Sonar is the movement of sound; it is also called echolocation. It occurs in our world naturally and, we can make sonar.  In the natural world many animals use sonar to hunt for food, to move around and in some very rare cases, to speak to one another.  It is a way for animals to see without using their eyes.  Think about bats, dolphins, whales and some birds. Artificial sonar (made by humans) achieves the same result. Anglers use sonar to effectively map their surroundings – to see what their eyes can’t. How Sonar Works The principal by which sonar works is actually quite simple.  A sound source (bat, dolphin) sends out a sound. Receivers on the animal await the return of that sound. (echo) The time it takes for the sound to bounce back off any objects or structure and returned to the animal tells how close or far an object is. The shorter the return time the closer the object – the longer the return time the further away it is. In fresh water, sound travels nearly 1500 meters per second, way faster than it does in air and this is the reason sonar technology works so well for anglers.  It’s FAST! A sonar unit will convert electrical energy into a single high frequency sound burst using the transducer.  The transducer will then await the return of that sound burst.  That information, or the speed in which it returns is then converted into a readable visual display and shown on various devices for angler interpretation.  The speed is the key here as the transducer can’t send out the next sound until the previous one has returned.  Isn’t technology incredible? So basically, sonar units tell anglers everything they need to know where to cast. Next: How to read your Sonar Unit.