In part 1 of this three-part series, we looked at the bass' sense of smell. Part 2 detailed how bass use their most relied-upon sense, sight. In this third and final installment, we look at the bass' second most-used sense, that of vibration or sound. We lump sound and vibration together because all sound is vibration and all vibration is sound. They are both sides of the same coin.
Once again, we confer with biologist and bass angler Gene Gilliland, Central Region Supervisor for the Oklahoma Department of Wildlife Conservation. Gilliland's decades of experience with bass make him an authority on all things Micropterus.
What's that sound?
This may or may not surprise you, but bass have ears. While they don't look like ours, they function much the same. A set of bones rattle when vibrations come across them and send a message to the nerves connected to them. This signal alerts the bass that there is something making noise. Our hearing does differ from the bass' in the range of sounds that we hear.
The human "spectrum" of hearing is generally recognized as between 20 and 20,000 hertz. The bass' range of hearing is considerably lower with the upper end being 200 or 300 hertz. This doesn't mean they can't hear as well as we can, it just means they hear a different range of sounds, akin to training whistles that pain dogs, but are inaudible to us.
"Basically, bass sense high and midrange frequencies with their ears, and low-end sounds with their lateral line," Gilliland explains. "Also, they tend to hear things when they are further off and 'feel' them with their lateral line as they get nearer."
As you've probably heard, there are also good and bad sounds that may spook bass. Most of the noise underwater is dull and constant. Gilliland says sharp, loud noises are extremely rare in nature, and will likely spook fish. Dropping something in the bottom of the boat will transfer to the water whereas a radio playing on the deck or talking anglers will dissipate into the air before reaching the water.
Things like trolling motors and depthfinders pinging will typically not spook fish unless they're turned on and off frequently (Gilliland hypothesizes that since a transducer's 'ping' is at 200 kHz, it is inaudible to bass). As previously mentioned, a constant sound approaching a bass has a far less likely chance of spooking him than a sharp, infrequent sound.
Gilliland relates the story of Chuck Justice, one of the top trophy bass guides in Oklahoma.
"Chuck has caught more 10-pound bass than anyone in Oklahoma. He doesn't mind running the trolling motor, it's turning it on and off that bothers him," Gilliland says. "He feels that turning it on and off puts them on guard. He'd rather keep it on, anchor up or drift than bump it constantly."
A bass' ears let him know that there is something going on around him, not exactly where a sound is coming from. Sound is easily distorted underwater, making it difficult to tell where a noise is coming from. Fish begin to home in on a noise when it is close enough for their lateral line to pick up.
"The closer a sound source gets to a fish, the more he uses his lateral line to tell where it's coming from," Gilliland explains. "There is one on each side of the fish, so it's kind of like them having binocular vision in that they can tell roughly where a sound is coming from with their lateral line and then know where to look for it."
Like sight, water clarity is a factor in what sense a bass uses. In muddy or murky water, their eyesight is compromised, so they'll rely more on sounds and vibration. The thump of spinnerbait blades or a curly-tail worm or a crankbait pulsing through the water all appeal to the bass' lateral line.
"Anything that moves underwater will make sound, though like a spinnerbait's blades, it may be inaudible to us," Gilliland says. "But, a bass can feel it in his lateral line."