What Can Bass Really Hear - Fish Tales

In part one of this Fish Tales series, we discussed the bass’ sense of smell, the anatomy and function of its nostril, fish attractants, masking agents and the lack of scientific research regarding attractants.  Many of us have heard that bass are spooked by noise from trolling motors, outboards, talking and/or movement in the boat.  Do these noises really have an effect on bass, and if so, do these noises decrease an angler’s catch rate?  Are these just “Fish Tales” or are there some facts to be discovered?  In this article we’ll focus on the bass’ sense of hearing, the anatomy of its inner ear and lateral line and their functions.  I’ll share published scientific research proving that sounds made by anglers, or their equipment, have a negative effect on bass.

When sound is produced, it travels in waves and is measured in terms of frequency (hertz) and intensity (decibels).  The distance and speed sound travels is based on the medium (air or water) in which it originates.  In harder or denser mediums sound travels faster. Sound travels thru water at approximately 5,000 feet per second while sound travels thru air at approximately 1,125 feet per second. These speeds differ slightly depending on depth, temperature, and elevation.  A sound wave originating in air that comes in contact with water undergoes reflection, refraction and transmission.  The amount of each depends on the surface condition of the water (flat or distorted).  Sound will reflect off any surface but the amount of reflection is based on the density of the object.  When the water surface is calm, most (if not all) of the sound will reflect off the water, change direction and continue across its surface.  This change of direction is called refraction; for example, even at great distances we can hear someone talking across a calm lake.  When there are waves present on the water surface, the sound wave is refracted in multiple directions and transmission is interrupted.  These facts are important to anglers in regards to talking while on the boat and spooking fish.  Due to the properties of reflection and refraction, a fish in a few feet of water may be able to hear us talking, albeit at a much lower intensity, while a fish in 20 feet of water may not hear a thing.

Now that we’ve discussed sound as it travels in air and water, let’s look at the anatomy of the bass’ inner ear and its function.  Unlike humans, the bass’ inner ear has no external connection, as it is located inside the skull.  The inner ear is divided into three sections.  The upper section has three semicircular canals for equilibrium that are connected to an open sac in the lower section called the labyrinth. Inside the labyrinth are three sensory patches (or maculae) called the saccule, lagena and utricule.  Each of these sensory patches contain a group of hair cells in which a calcified ear stone lays on top with a thin membrane dividing the two.  As sound reaches the inner ear, the stones move across the maculae and stimulate hair cells that send a message to the brain.  Once the sound is received in the brain, the bass goes thru three phases: an initial arousal and evaluation phase, a search phase, and a close up analytical evaluation phase.  Bass rely on their sense of hearing to detect prey, predators, and other activity in the area.

In conjunction with the inner ear, bass use their lateral line to detect movement within close vicinity.  Vibrating objects (including lures and fish) push water molecules, which push other molecules, and so forth.  The result of this pressure is called hydrodynamic disturbance and its strength is measured in terms of water displacement, acceleration, and velocity.  For example, a subtle swimbait will displace less water than a wide wobbling fast moving crankbait.  A bass detects this vibration thru its lateral line and this is why vibrating baits like crankbaits, spinnerbaits and chatterbaits are so effective.  The lateral line (the lateralis system) is a series of pores which open into a canal like system that run from the gill plate to the tail and also across the bass’ head and face (the cephalic system).  Between each pore lies a gelatinous mass, the cupula, which rests on the canal floor over the hair cells.  As water flows in thru the pores and over the cuplula, a distortion of the gel occurs that bends the underlying hair cells.  The hair cells then send a series of nerve impulses to the brain, which are analyzed.  The lateral line system measures the temporary change in water flow and local disturbances in the environment.  Bass use their lateral line to detect the movement, direction, and distance of prey and predators.

Now let’s examine the research I discovered regarding this topic.  I conducted my research in the same manner as my previous article by using various scientific search engines on the Internet.  During my search I found only one study regarding bass and sound.  The study was conducted at the Fish Ecology and Conservation Physiology Laboratory at the University of Ottawa, Ontario, Canada by Ashley Graham and Steven Cooke.  Their study focused on the effects of noise disturbance from various recreational boating activities common to inland waters on the cardiac physiology of the largemouth bass (micropterus salmoides).  In the study they took nine largemouth bass, exposed them to three different sounds, measured the largemouth’s cardiac response and then measured how long it took for the bass to return to its baseline heart rate.  All nine bass had a probe surgically implanted into the aorta which measured cardiac response to the sound presented.  In order to create a controlled environment, the researchers created a water filled box that kept the fish from seeing the researchers, the sound apparatus and the other fish.  The box also had a wave baffle between the fish and the sound apparatus to keep any water disturbance from reaching the bass . Once the probes were implanted, three bass at a time were put into the box and each sound was introduced.  The bass were exposed to each sound stimuli (oars paddling in the water, a trolling motor, and a 9.9hp outboard motor) for 60 seconds while their heart rate was monitored and noted along with the amount of time it took to recover.

The fish were tested over multiple days and each sound was given in random order to prevent any conditioning.  The study measured three cardiac responses of the bass when the sound was introduced: the stroke volume (the volume of blood pumped from one ventricle of the heart with each beat), heart rate (the number of heartbeats occurring within a specific length of time) and cardiac output (the volume of blood pumped by the cardiovascular system per minute).  The researchers chose cardiac response as their stress indicator since previous research revealed that cardiac output is a sensitive indicator of fish stress and has been used to assess responses to exercise, air exposure, water temperature alterations, handling, and other human activities.  After exposing each bass to all three sounds, the researchers found that there was a straight correlation between the intensity of sound as it affects heart rate and recovery time.  The paddle had the least effect with a recovery time of 15 minutes, the trolling motor had a medium effect with a recovery time of 25 minutes and the outboard motor had the greatest effect with a recovery time of 40 minutes.

This study is important to bass anglers as it gives us some factual information about how specific sounds cause a stress response in bass. The downside is that the study has some limitations.  First, the noise presented was kept a constant distance from the bass and therefore proximity in a field setting may have a different effect on the level of cardiac response.  For example, fish that live in a lake that has high volumes of boating traffic and fishing pressure may not elicit the same response to these noises since they are exposed to them on a regular basis.  Second, the noises presented were abrupt and could have elicited a startle reflex.  Bass have a pair of nerve cells, called Mauthner cells, which run on either side of their back.   Their purpose is to aid in the escape from attacking predators by quickly triggering the bass to move away from danger.  The startle reflex engages when a sudden change in sound intensity is present such as a starting a boat engine, rubbing the bottom of a boat on a rock or tree, a loud splashing lure and putting down a trolling motor too loudly. This is an important fact for anglers to note since these are all sounds we produce on a regular basis while out on the water.  In order to avoid activating the startle reflex, it’s import that we present our baits with as little sound as possible especially if bass are close the surface.  Third, the study only focuses on the bass’ cardiac response and not any effect this response has on catch rates.  Since we know that specific sounds have an effect on cardiac elevation and the startle reflex, it’s safe to assume that if a bass detects a non-prey sound, they will likely be on the defensive rather than in the hunt-mode.

So in the end, it appears that we gained some knowledge but this Fish Tale will still remain somewhat shrouded in mystery until a researcher completes an experiment that includes sounds related to angling, their physical effect on bass and the catch rate.  I hope this article has provided you some insight about bass’ sense of hearing and its function, the anatomy of its inner ear and lateral line and some understanding regarding sounds generated by anglers that can affect bass’ behavior.  Until next time, stay focused and fish hard and I’ll see you out on the water.

Resources:

1. Unknown author. (January 28, 2011). Speed of Sound. Wikipedia. Retrieved on 1/29/11 from http://en.wikipedia.org/wiki/Speed_of_sound
2. Unknown author. (No date listed). Behavior of Sound Waves. The Physics Classroom Tutorial. Retrieved on 1/29/11 from http://gbhsweb.glenbrook225.org/gbs/science/phys/Class/sound/u11l3d.html
3. Dr. Keith Jones. (2002). “Knowing Bass- The Scientific Approach to Catching More Fish.” Gilford, CT: The Lyons Press
4. Graham A, Cooke S. (March 5, 2008) The effects of noise disturbance from various recreational boating activities common to inland waters on the cardiac physiology of a freshwater fish, the largemouth bass (Micropterus salmoides). Fish Ecology and Conservation Physiology Laboratory, Institute of Environmental Science and Department of Biology, Carleton
University, Ottawa, Ontario, Canada.