Inside Angles: The Great Sonar Spooking Mystery

Affiliate Disclosure: This page contains affiliate links. We earn from qualifying purchases.

---

Professional walleye angler Gary Roach was the first I remember suggesting that fish become wary of, or get turned off by, sonar pulses. He would strategically turn off his electronics, at times, once he found fish, both on ice and open water. Some anglers, including Roach, believed this phenomenon remained at play when LCD technology hit the market in the mid 1980s, and throughout other sonar advancements along the road to today.

Meanwhile, we kept looking and experimenting but could not see definitive evidence of the claim, although early on we certainly addressed the fact that fishing pressure was often at work making fish wearier and difficult to catch. In-Fisherman has also always been all about the science involved, but science, too, did little to address the mystery of whether fish could hear or feel sonar pulsing.

With the advent of live-imaging (forward-facing) sonar, even more anglers are questioning the effects of sonar on fish behavior and the bite. So staff fishery scientist Dr. Rob Neumann, along with former Senior Editor Steve Quinn, now a Field Editor and also a fishery scientist, dug into the science, while our Screen Scene columnist and Digital Content Manager Thomas Allen questioned high-profile anglers about their experiences with the technology.

I believe publication of “Live Sonar Effects on Fish Beneath the Ice,” in this season’s Tactical Ice Fishing Guide, to be the present industry standard on the subject. You can read the article for yourself, but we want to offer a synopsis of the science as our staff scientists revealed it.

Humans detect sounds between about 20 and 20,000 cycles per second (Hertz, Hz), while bass hear sounds from about 10 to 600 Hz, with peak hearing sensitivity around 100 Hz, as determined by extensive lab experiments performed by Dr. Don McCoy at the University of Kentucky. That hearing range is probably like other common freshwater sportfish, while minnow and catfish species have a probable hearing range that spans higher frequencies to perhaps around 13,000 to 15,000 Hz.

Fishing sonar systems operate with the transducer emitting directional pulses of sound into the water. If the sound waves hit an object such as bottom, fish, cover, or even your lure, the transducer then receives the “echoes” of sound waves that are returned or “bounced off” those objects, and the unit then converts those signals into a visual picture on your sonar screen.

So, can fish “hear” sound waves emitted by a transducer? Most traditional fishing sonars operate within frequencies between about 50 and 200 kHz (kilohertz—one kHz equals 1,000 Hz), which the science tells us is well above the 10 to 600 Hz hearing range of bass and other freshwater fish. Side- and down-imaging operates in the ranges of around 455 to 800 kHz. CHIRP sweeps through a range of frequencies. Garmin reports that LiveScope operates at 530 to 1,100 kHz, which also is well above the hearing range of bass and other fish.

So the science tells us fish shouldn’t be able hear the pulse waves from any of the sonars we’re using. But can they “feel” sound waves produced by sonar with their lateral-line system? This sensory organ allows fish to detect movements, changes in water flow, and vibrations of the lowest frequencies. The acoustic wavelengths detected by the lateral line—from about 1 to 200 Hz—overlaps with hearing detection on the lower end of the scale. That range is substantially lower than fishing sonar frequencies.

So fish also shouldn’t be able to “feel” the pulse waves from our sonars. But that doesn’t solve the mystery.

According to the science, fish and humans can’t feel or hear fishing sonar pulses. But we often can hear an audible repeating tick that’s emitted from a sonar’s transducer. We need to look further into what causes that ticking sound, but perhaps caused by the energy being applied to the transducer element or elements, which then vibrate at specific frequencies to produce the acoustical sonar signals.

Since we can hear the tick, it’s obviously in our hearing range, but without knowing the sound frequency of the tick, we don’t know whether bass can hear it. So while fish may not hear or feel the sonar sound signals themselves, sonar units might still be creating noises that they can hear.

Neumann questions, if fish can “hear” the repeated ticking, is it possible that they shy from it or become conditioned to it? And how do other subtle sounds that might be transmitted from electronics affect fish? Do sonar units produce harmonics outside the operating frequency range that fish can feel or hear? Does increased unit power (wattage) and/or the strength of the signal in decibels enter the picture, even if not in the hearing range as we know it? Future scientific studies could help answer these questions.

So, it remains plausible that when continually “shined” with forward-facing sonar, fish may begin to change their behavior. There are mixed reports on how it may or may not affect certain fish species, a discussion for another day.

Certainly, the use of live sonar has shown us that, for whatever reason, many fish react to our presence. Whether it does or does not have anything to do with the sonar, we’ve long surmised that our presence often can be repulsive to fish.

Practical experience suggests that fish move away from a boat moving over them, so we use boards and other measures to move lures away from the boat. We know that sometimes we can’t get close to fish if we’re going to get them to bite, so at times we stay a long cast away to make our presentations. I could go on and on, with examples from ice fishing or open water.

Again, we have long surmised that our presence often affects fish behavior, but now we literally see it in real time and at a distance with live sonar. We’ve solved part of the mystery; we’ve moved the ball a bit farther down the field; but we still don’t know answers to everything that’s at play.

---