Your depthfinder, your motor, even your voice may be spooking fish. Lenny Rudow from Edgewater, Maryland, is fishing editor for Boating magazine, author of numerous fishing books, and a renowned seminar speaker. He’s keenly interested in all things fishing, and he tests boats, and fishes, around the world, including freshwater and saltwater, inshore and offshore. He’s conducted studies on noise and its possible impact on fish, and while unscientific, the studies yielded very surprising results.

Rudow once obtain permission to float an 8-foot plastic bass boat on the National Aquarium in Baltimore, Maryland, to test three depthfinders. In the aquarium were sharks, rays, snook and tarpon.

When dolphin, tuna and marlin attack lures and baits in a trolling spread, it is possible for them to hear voices from the boat. Underwater studies have shown voice can be detected 50 feet behind a trolling boat and three feet underwater.

When the first depthfinder was turned on, it appeared that some of the fish might have been avoiding the boat. It was even more noticeable when two depthfinders were on. When all three were on at the same time, there was no doubt fish were intentionally staying out from under the boat.

Depthfinders emit a sound wave to detect and mark the bottom and fish, and Rudow isn’t sure if it’s the sound, vibration or something else about depthfinder sound waves that fish hear and/or feel. But since the test, when he has arrived at his spot and begun fishing, Rudow will switch off his depthfinder, especially if the fish aren’t biting.

Another noise study, this one in a tributary river to Chesapeake Bay in Maryland, involved motor noises with 12-volt and 24-volt electric trolling motors, and 2-stroke and 4-stroke outboard motors. An underwater microphone (hydrophone) to pick up and record the noises, and a dB-A meter to measure the sounds in decibels, were used.

As expected, the 12-volt electric trolling motor with its slower prop speed was very quiet. The 24-volt trolling motor was twice as loud, and the 4-stroke gas motor was louder yet. But what was surprising was the outboard motor – it made considerably more noise when in neutral, than when it was in gear! Rudow believes the internal parts aren’t under pressure when the motor is in neutral, and this allows them to bang around. There’s significantly less commotion when the motor is in gear because the parts are working together smoothly. Keep that in mind when attempting to quietly slip into a fishing spot.

Rudow also made a startling discovery while 40 miles out to sea off Ocean City, Maryland, researching motor and boat noise. A hydrophone was trolled 50 feet behind the boat and three feet down, right where some of the lures and baits would be in a trolling spread for tuna and marlin. When the recorded sounds were reviewed and analyzed, as expected there was plenty of loud noises from the motor and the turbulent water as it churned past the microphone. However, strikingly, above all that racket, Rudow could hear the voices of the people in the boat’s cockpit! While it could not be understood what was being said, Rudow said there’s no doubt they were voices. He described them as sounding like the muddled adult voices in the Charles Schulz Peanuts cartoons (Charlie Brown, Snoopy and friends).

Offshore fishermen often say a marlin was “window shopping” when it flashes through the baits but doesn’t strike. But there may be more to it than that. Anglers jump up and holler at the awesome sight of a marlin crashing a trolling spread. It may be those loud voices that discourage the fish from striking.

Noise may be having more of an impact on your fishing than you realize. Shhh! . . . keep it down when you’re on the water, you just may catch more fish.