In northern and middle Atlantic waters, in deep water, or in low-light conditions we can’t see the fish’s reaction to the sounds we make. As a result we have an “out of sight out of mind” mentality. In fact, every time you make a loud noise, every fish within casting distance can “hear” you, by sensing the vibrations with its lateral line. And they can hear your boat, too.
Part of my research consisted of dropping a hydrophone down 15’ in a 20’ deep, and listening to the sound levels created by different things we anglers do on a regular basis. The hydrophone was interfaced with a db-A meter (the same thing police use to measure sound levels at rowdy parties) so each noise could be measured quantitatively.
As one might expect, outboard motors created noise under the boat. Both two and four-strokes were about twice as loud as an electric trolling motor, though the majority of the noise was caused by the propeller – not the powerhead. Here’s where it gets interesting: while a four-stroke remains quiet in or out of gear, a two-stroke creates lots of loud chatter when shifted into neutral. The same rattle-clank-bang of metal on metal which you hear above the water transmits below, as well. So if you run a two-stroke, you’re best served by motoring towards your hotspot and shutting down while the motor remains in gear, instead of shifting into neutral and allowing the motor to idle.
What about the four-stroke and inboard guys? They have it made, right? Not exactly. No matter what type of power systems you have, fish will still hear the whine of the prop. At slow speeds, this usually isn’t a big deal and at high speeds, you probably don’t care too much if you scare the bejesus out of a few bluefish. But there’s one more major-league way our boats spook fish: shifting gears. Even a smooth-shifting transmission creates a clunk that fish don’t like. You don’t believe me? Fine—next time you pull up to a floating board and see mahi-mahi underneath, tease them to the surface then shift in and out of gear. The fish will scatter. Or wait until you find a pod of stripers on the surface, chewing through a school of bunker. Idle up close, shift to neutral, then go into reverse. By the time your boat comes to a stop, the smart money says the frenzy will be over.
Charged Up
The guys with a 35’ express in our marina were downright pitiful: all season they’d struggled to catch fish, charter bookings had plummeted, and then their boat had been pulled because galvanic corrosion chewed away half of their running gear. A few weeks later when I saw them on the docks, they were complaining that their zincs had disappeared. Ahhh….suddenly it all fell into place.
I walked to the truck, got my voltmeter, and connected the negative lead to their battery. Next, I clipped the positive lead to a bare wire and dropped it into the water. My meter read 0.93 volts—way too high (natural voltage should be between 0.7 and 0.8 volts). When I told them they had an electrically “leaky” boat, the problem quickly surfaced: during a refitting over the winter, part of the bonding wire had been ripped out. They hadn’t replaced it yet. To make matters even worse, an extra house battery had been installed and out of convenience a washdown pump (with a through-hull fitting) had been connected to it. No wonder these guys were having a lousy season – they were frying the fish.
Electrolysis naturally causes a tiny electrical charge in the water, around your boat (or around any other item with metal in it, for that matter). But if your boat isn’t properly bonded, old or cruddy connections can “leak” additional electricity into the water and change that natural charge. Fish, meanwhile, are either attracted to or repelled by this charge. Some claim that positive charges attract fish and negative charges repel them; some other people claim that different fish are attracted to different specific charges. Pro-Troll (the makers of a “black box” unit which controls the charge on downrigger wires) and S2 Instruments (the company that produces the Mako Magnet) both claim to have figured out how to attract fish with specific electrical charges. Manufacturer claims are always suspect, but one thing is clear: electrical charges in the water have the potential to spook the fish, and drive them away from your boat.
Wondering if electricity explains why fish don’t like your boat? Then give it the test, as described earlier. All you need is a voltmeter that reads between zero and one volt, and a length of bare wire. Try it away from other boats so they don’t effect your readings, and if you find a natural voltage other then 0.7 to 0.8 volts, start looking for potential leakage by turning on and off all the electrical items on your boat, one by one. When the meter spikes, you’ve found the offending unit.
Ping Me
One other fish spooker few of us ever think about is the pinging of our fishfinders. Many electronics experts will swear that a fish can’t hear a fishfinder. But if you fire up a fairly powerful unit with a transom-mount transducer, you can hear the “tock… tock… tock” yourself, when you lean over the transom. And, while doing research for an article several years ago, I saw something with my own eyes that convinced me beyond the shadow of a doubt that yes, fish can sense an active fishfinder.
For this particular gig we were granted permission to launch a small boat in the massive, 500,000-gallon saltwater tank in the National Aquarium in Baltimore. I’d mounted three fishfinders and transducers on it; all were fairly weak units in the 100 – 300 watt range. A second journalist was posted two flights below, watching as fish passed under the boat. We communicated via FRS radio, and she alerted me whenever a specific fish was about to be pinged by the finders. Our mission was to determine if I could differentiate between species with any of the three units. (Nope—it was impossible to tell if the marks came from a snook or a sand tiger.) The fascinating discovery we made, however, was that certain fish started avoiding the boat when the fishfinders were fired up. Sharks and rays, in particular, showed a clear dislike of swimming through the transducer cone.
Now, we’ve all caught fish with the fishfinder going and I’m not about to claim fish are aggravated by those sonar waves. But they can, in fact, detect them—which means the fishfinder could have an effect, be it positive or negative, at any given time in any given situation. This is particularly true when sharking, judging by the response of the sharks in the aquarium.
Lucky for us, all of the fish-spooking effects of our boats can be minimized or eliminated with a bit of foresight. We can coast into the hotspot, cease shifting in and out of gear, test for electrical leakage, and turn the fishfinder off. Of course, we still have to be careful not to slam that hatch, drag that tacklebox across the deck, or drop that sinker on the deck. And if we are, that catch rate will soar.
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