Bass lateral lines run the full length of their body. They include a row of pores filled with water and nerve endings. The lines are finely tuned to detect water displacement (disturbance or changes in water motion). They help bass determine vibration from prey or a predator, how close it is, how big it is, and which direction it’s moving. The response depends on how close movement is to the bass.
Burns Phillips at bassfishingandcatching.com explains lateral lines are tuned naturally to detect subtle low-frequency (1-80 cycle) vibrations created by small prey such as minnows. It’s an ear of sorts that detects vibrations resulting from water displacement. This detection can occur at a significant distance if background noise is at a minimum. Bass associate specific sound wave patterns with specific prey. A bass would not confuse water movement of your cell phone falling from your shirt into the water with that of a school of shad or even a single jumping shad.
Vibration is most important when water conditions limit visibility. After all, a bass is first and foremost a sight feeder. Beyond four or five feet, bass hearing is much more important. However, vibration occurring five body lengths away may well arouse its attention and move it to investigate the source as a potential meal. From such a short distance, the lateral line is deadly accurate and partly explains why even blind bass are able to feed and survive.
It can be said that a lateral line, while playing an important role in feeding, is rarely the single determining factor for a bass striking fishing lures or prey beyond an area close to its body. Lateral lines aid in detecting water movement, arousing the bass’ attention, and helps guide it closer to movement so it can see if the movement is food and strike.
The lateral line sensory system is directional. The inner ear is not. Both make it easy for a bass to pick up vibrations from lures like crankbaits. For example, a rattle bait moving toward a bass from 40-50 feet away emits high-frequency sound waves from rattling shot and hooks. The bass’ inner ear receives those sound waves, but is unable to determine the exact direction of travel. Lower frequency vibrations from a wobbling lure emit pressure waves that are felt (heard) by the lateral line and provide bass a source of direction.
When detected, water movement is soft like that emitted by quiet, plastic worms, lizards, or grubs bumping rocks or stumps. Lateral line sensitivity even alerts bass to the possibility of a meal. When compared to crankbaits or other hard plastic baits, soft lures more closely resemble sounds and vibrations made by natural prey.
In both cases, bass will be aware something is out there via its hearing and lateral line, but probably does not consider it significant. As vibrating or quiet lures come closer, vibration and sound reach the transition stage where both are strongly received. The fish then combines its sight, hearing, and lateral line to determine location, direction, and identity of the lure.