Anglers have countless theories on how, when, and why they spook fish, and we took an in-depth look at the topic in Scaring Fish: Sensory Overload, a couple of years ago. At the moment, however, let's focus on one gigantic fish-spooker in particular: your boat.
Work has taken me south for substantial stretches of time every winter going back over two decades, and long ago I noticed that many Floridians are keen to maintain a stealthy attitude at all times. Anyone who’s been on a flats trip has surely been shushed a few times by the captain. This is because they can often see the fish they’re pursuing from 30 or 40 yards away and watch them get spooked. Here, however, it’s rare we can actually see the impact we have when we make noises with something like, say, a stereo system or an outboard motor. As a result of those Florida trips I wondered for years just how much noise we make beneath the surface of the water, and to find out, I got a hydrophone (an underwater microphone) and interfaced it with a dB meter (which measures sound levels). I measured the sounds underwater at different depths down to 50 feet on a half-dozen different boats, in different conditions. There was one overarching take-away: Sounds and vibrations travel through the water at a similar intensity level as they do above-decks. In other words, if you listen to an old rackety-clank two-stroke outboard underwater, and then listen to a whisper-quiet modern four-stroke, the difference between the two is just as significant beneath the surface as it is above. If a hatch slams with a startling, gunshot-like noise, the sound is just as startling 20 feet below your boat. And if you’re yelling to be heard over the rumble of an idling diesel, your voice is also going to be louder than that diesel when listened to from a fish’s point of view.
Recently, an angler complained that someone else fishing nearby had failed to turn off his (four-stroke) engine, and as a result, killed the bite. But, had every angler on both of those boats remained mute? Had anyone aboard either boat closed a hatch, rifled through a tacklebox, smacked the hull with a jig-head, or dropped a lead weight on the deck? I’d bet my bottom dollar that any one of these factors had a whole lot more to do with shutting down the bite than an idling four-stroke outboard – which is just as quiet underwater as it is from above, with the loudest noise it makes coming from the tell-tale squirting on the surface. A starter engaging the flywheel on any type of motor, however, does make a loud sound underwater. So it’s entirely possible that an outboard being shut off and re-started over and over again has a bigger impact than that constantly-idling four-stroke, much less be overshadowed by a shout or a stomp on the deck.
A few weeks ago the whole topic reared its head again while I was interviewing Dr. Arthur Popper, Professor Emeritus and Research Professor at the University of Maryland’s Department of Biology and a well-known expert on fish hearing, for an upcoming article. We talked a lot about what and how fish hear, but one comment stood out. “Almost all fish – almost all animals – use hearing to get a big-picture view of what they can’t see,” he said. “This is called the ‘acoustic scene,’ and it’s no different than the way we use our hearing to know what’s going on around us even when we can’t necessarily see it.”
Now ask yourself which is more likely to startle a deer in the woods, a bird in the tree, or a rabbit in the yard: humming softly as you walk, or walking silently and then suddenly clapping your hands? Which sets off the louder alarm bells in the acoustic scene? What noises do you make on a boat that relate?
There’s a lot more to this topic and I could go on and on, but I’ve already violated my space constraints for this column. Suffice it to say, I believe strongly in maintaining stealth whenever and however possible, but I also think many noises, engine noise among them, may often be misunderstood in this regard. Beyond this, I can’t let it go without mentioning a few other lessons learned from listening to the sounds of the underwater world:
- Shifting an engine of any kind into gear makes a loud “clunk” underwater, which is very effective at scaring fish.
- In most situations the noise most consistently heard underwater is created by people on the boat speaking loudly, laughing, or yelling. Yelling probably accounts for spooking more fish than any other single factor.
- The choppier it is on the water the more background noise there is, which helps to mask the sounds you make. (Note: one of the things Dr. Popper mentioned was that the level of background noise has a big impact on how well fish hear things; in human terms he compared it to having a quiet conversation in private versus in a crowded restaurant). So the calmer it is, the more imperative stealth becomes.
- Some rattling lures (Rat-L-Trap, we’re talking about you) are amazingly loud underwater. Some folks believe they can do more harm than good in tranquil conditions, and I don’t doubt it.
- If your boat has hatches that slam and you want to do yourself a favor, buy some stick-on rubber bumpers and put them where the fiberglass meets; they do turn the “crack” into a “thud”.
Read the article with more of Dr. Popper's insights, The Fish Are Listening.