Sound Advice

This is a condensed version of part of a chapter in Orvis Guide to Fly Fishing for Coastal Gamefish. To read the full chapter in more detail, plus all of the other great information contained in the book, you can purchase it here.

The Importance of Sound to Your Fishing
Many anglers make assumptions about what fish hear, and many of these assumptions are wrong. Since fish don’t have external ears, many people think they can’t hear. This is also not true. Water is 850 times denser than air, so sound travels very well in water. Sensing that sound is very important for fishes, both to find prey and to avoid predators, as well as for social behavioral reasons like finding and communicating for reproduction.  Dropping items in a boat, splashing while wading, a splashy presentation of a fly are all actions that send sound waves propagating rapidly through the water, alerting fish to your presence. But designing flies that put out vibrations as they are stripped through the water (vibrations are essentially low frequency sound waves) can be deadly in bringing in fish. Understanding how fish detect sound, and how sound travels through water can be useful in creation and selection of flies, as well as for strategizing how flies are fished under different conditions.

Basics of Sound in Water

Sound is more important in water than most anglers realize. Much of the misunderstanding likely results from a property of sound waves – they typically don’t travel from one medium to another, from water to air, for example. The densities of water and air are too different for most sound to travel from one to the other, so anglers on a boat or wading are oblivious to most of the noise that exists below the water surface. Similarly, fish are generally unaware of sound traveling through the air above them.

A sound wave is a pressure wave that includes two linked components – pressure and particle motion – that are difficult to separate, so for the remainder of the discussion I will use the term ‘pressure’ to refer to both.  In any case, these waves displace particles as they travel through air, water, or other medium. Sound in water travels approximately 4.5 times faster (and also travels farther) than in air. Low frequency sounds tend to travel farther than high frequency sounds.  This means that the noise made by dropping a reel on the deck of the boat is detected almost immediately by fish within a significant radius of the boat – the boat hull acts as an amplifier, and since it is in the water, the sound of banging against its hull is transmitted through the water.

Pressure waves are also generated by objects moving through the water – whether a swimming fish, a scurrying prey, a moving boat, or wading angler. These waves travel through the water in the same fashion as sound waves. This is why stealthy anglers are more successful when wading than those who move quickly across the flat, pushing a wave of water as they move.  This also explains why a fish reacts to a fly that plops loudly into the water, sending ripples across and underneath the surface.
When sound travels through water, its intensity diminishes with distance. This is because as a sound wave travels through water, it is weakened by scattering and absorption. Scattering is the reflection of the sound wave in directions other than its original direction of movement.  This can be caused by structures such as rocks, and by the bottom or water surface, both of which are different densities than water.  This is especially true in shallow water, where the bottom and water surface are close to one another, and greatly limit the distance that a sound wave can travel relative to the open ocean.  In deeper waters the bottom and water surface aren’t as influential, and sound can travel farther. Absorption is the conversion of the sound energy to other forms of energy, and doesn’t differ between shallow and deeper water.  

Fish Hearing

The propagation of sound and other pressure waves in water means that detection of these waves is an essential characteristic possessed by gamefish, their prey, and their predators. Fish have two means for detecting these sound and pressure waves (and the associated particle displacement) – an inner ear and a lateral line.

A fish’s inner ear is composed of a series of fluid filled canals and chambers.  The inner walls of the chambers are lined by cells with hair cells – hair-like extensions that protrude into the chamber. In these chambers are small bones, called otoliths. As the otolith moves around in the chamber, the cilia detect the movements and send a signal to the brain.  This is also how, just as with our inner ear, fish can control their equilibrium – the otoliths lying on the bottom, side, or top of the chamber tell the fish it is swimming upright, on its side, or upside down, respectively. 

More important to this discussion is how this setup is used to detect sound. As a sound wave travels from the water to the otolith, it is moving between substances that have different densities. This causes the sound wave to change shape, and causes the otoliths to vibrate differently than the rest of the fish. The vibration of the otoliths stimulates the cilia, which sends a message to the brain. The brain then has to determine whether the sound is of consequence, and whether it is from a prey or predator.  The sound waves traveling through the fluid within the inner ear can also be detected.

To use the pressure components of sound, some fish use their air-filled swim bladders to increase their hearing ability. The air within the swim bladder is compressed by the sound waves, so is more sensitive than the inner ear.  In many fish, the swim bladder is connected to the inner ear, which allows the air bladder to act as an amplifier of sound (the swim bladder acts like a transducer, re-radiating the pressure components of sound as particle motion to the otoliths). Even in many fish without a direct connection between the swim bladder and inner ear, an extension of the swim bladder is close enough to the inner ear to at least partially amplify sound.  The inner ear system of fish is good at detecting sounds at both close range (within 30 feet or so) as well as from distant sources (a mile or more in open ocean).

A great compliment to the inner ear system of fish is their lateral line system. The lateral line is a series of pores, through which specialized cells extend. The lateral line extends along the length of the fish, from just behind the head to the base of the tail. Sticking through the pores are specialized cells, called neuromasts, that contain sensory cells embedded in a jelly-filled casing called a capula, which extends into the pore. As pressure waves pass over the fish, the capula is moved, which in turn moves the sensory hairs within it, which sends a signal to the brain. The lateral line detects the particle motion aspect of sound from near sources, 30 feet or less.

The movement of pressure waves through the water, and the ability of fish to detect them is why flies like seaducers, muddlers, sliders, and poppers can work so well. All of these patterns produce pressure waves as they move through or across the water. So even in low light or murky water, fish are able to detect these flies.  But don’t just reserve these flies for low light or murky water conditions – fish frequently first detect prey (or your flies) from a distance using sound (or pressure waves from motion), and then rely on sight only in close quarters.

Fly Design

When strategizing the creation, selection, and presentation of flies, I start with the basics and add on components if the situation requires.  Step one is to determine the conditions in which I’ll be fishing. Do I need to be prepared for murky or clear water, backcountry water that is tannin-stained or the crystal clear water of a tropical flat?  It’s always a good idea to have flies for sunny as well as cloudy days. What about the species I’ll be targeting – are they adapted best to feed in bright or dark conditions, clear or murky water? The answers to each of these questions is critical to designing, selecting, and presenting flies in coastal waters.

Let’s start with murky coastal waters, because I think this situation allows the most basic approach, but realize that the importance of sound and motion (both of which cause pressure waves) is also important in clear water. Since underwater visibility is greatly limited, gamefish primarily use their lateral line and inner ear to locate prey, and vision becomes important only at close range. For this reason, a fly’s motion and sound are the most important characteristics to consider. A whistler with a full, webby hackle collar pulsates with every strip, sending out pressure waves that can be detected by gamefish.  Similarly, Mangrove Muddlers and other similar patterns that push water as they are stripped can be located by gamefish in murky waters. Of course, poppers can be very productive in poor visibility conditions – the ‘pop’ sends out strong pressure waves, followed by weaker pressure waves from water drops splashing down. Plus, you can alter the strength of the popper’s pressure waves by changing how strongly you strip the fly.

Do artificial noisemakers actually work to attract gamefish? Despite the prevalence of rattles and other noisemakers on the market, we don’t know the answer to that question. Rattles, for example, likely create sound at a frequency that is too high for most gamefish to hear. However, things like ‘clackers’ likely produce sound at a lower frequency, which gamefish are more likely to hear. In either case, it’s important to not overdo it. Remember that prey tend to minimize their output of pressure waves – whether sound or motion – to escape detection by predators, so too much noise emanating from a fly can actually keep gamefish away.

In murky water conditions, it’s important to work the fly slowly. This gives a fish the chance to find the fly. Your strips of the fly can be varied – from strong and fast to gentle and slow – but you should give ample time between strips to allow the fly to stay in the water for a sufficient amount of time. Keeping the fly in the water longer allows time for the waves generated by the fly to travel through the water and be detected by the fish’s lateral line or inner ear, for the fish to determine the source of the movement, move toward the fly, and once close enough, visually identify the fly and eat it.

Other conditions present similar challenges for gamefish to locate prey, such as nocturnally feeding fish. Dusk and dawn are a bit along the continuum, where the relative importance of sight increases.  This should be reflected in your flies and how you present them. Under each of these conditions (dark of night, dawn, and dusk), gamefish rely heavily on motion/sound to locate prey, and the relative importance of sight changes with the changing conditions.

At night, there is so little light that sound/motion and contrast are the only factors I consider for flies. A fly that moves water can be located by a gamefish, and since I expect a nocturnally feeding fish to be adapted to seeing in low light conditions, I use a black fly that contrasts well with the star- or moon-lit sky to a fish feeding from below.  This strategy works well for anglers fishing for striped bass at night.

At dawn and dusk, the gamefish is exposed to constantly changing light conditions – at dusk there is less light with each passing minute, whereas at dawn light level is increasing over time. When fishing for tailing red drum in late evening and into dusk, I usually start with a fly that contains flash of colors that red drum can see. Gold or copper and green flash on tan or brown flies are my favorites. As dusk approaches, I often switch to a fly that is darker (so it provides a profile or silhouette) and moves water, such as a muddler, seaducer, or even a surface fly such as a gurgler.

Dawn patrol provides a bit of a different challenge. Light is initially very low, so flies that move water and provide good contrast are essential. As light levels increase, however, color can become important very quickly, so even the flies that rely on motion and contrast for low light dawn conditions should have appropriate colors.  The importance of light at dawn changes quickly enough, I believe, that if you rely on changing flies to keep up with these light changes, you will be forever behind the curve. This is why, when fishing at dawn for tarpon, I usually tie on a black or purple toad – the toad provides the motion necessary for tarpon to find the fly in low light conditions, black and purple provides sufficient contrast in low light (though not as good as black), and as light levels increase, tarpon are able to see purple.