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The Hidden World of Bass Sound Detection.

We anglers tend to interpret animal behavior from our own point of view and sensory abilities. Though our vision pales in comparison to birds and some other animals, we rely on sight for nearly all our daily activities, not the least for eating. The Bill Lewis Company has produced and sold more than 150 colors of the Rat-L-Trap because anglers tend to focus on lures' visual appeal. Bass pros and their disciples worry over slight differences in tint among plastic worms labeled "green pumpkin," as if bass could tell the difference.

But when we jump into the water to snorkel or scuba dive, we hear nothing but own our exhalations. For centuries, mariners and scientists generally regarded the aquatic world as a quiet, as referenced by Jacques Yves Cousteau's famed film, "Silent World," released in 1956. Since then, scientists have learned a lot about sound under water and how fish species respond to it.

Sound Science

Physics informs us that because molecules in water are much closer together than they are in air, motional energy is transferred faster and sound waves travel 4.8 times faster in water than in air, at almost a mile per second. Lower-frequency sounds can travel amazingly far. In his book, Knowing Bass, long-time bass sensory researcher Dr. Keith Jones noted that when the Soviet Union launched their notoriously noisy "Alpha-class" submarines off the coast of Norway in the 1970s, a U.S. Naval Intelligence listening station in Bermuda picked up the sounds, some 4,000 miles away. "There's a much higher level of ambient sound under water than there is in air," Jones says, "including man-made, weather-related, and the sounds of fish and other aquatic creatures."

Under water, any movement of water, such as that generated by fin movements, water currents, or the movement of a lure through the water is considered an acoustical phenomenon, as are the compression waves that emanate from a sound source. This characteristic of sound in water has led to the evolution of a lateral-line system in fish and some aquatic amphibians to interpret underwater vibrations and sounds of the lowest frequencies. This system works in conjunction with the inner ears of fish to decipher the direction and meaning of sounds. This organ is easily observed on the sides of bass and other common species as a series of pores extending from the head region to the beginning of the caudal fin.

Because of their need to maintain a streamlined shape, fish lack an outer ear that helps funnel sound waves to animals or birds. And because they live in an aquatic environment, they don't need a middle ear, such as the human ear drum, to transduce compression waves in air into the movement of fluid that in turn stimulates hair cells in the inner ear, leading to hearing. The inner ears of fish are similar in most ways to those of humans and other terrestrial vertebrates, with a system of connecting ducts and chambers and containing calcareous ear stones called otoliths.

Because fish are about the same density as water, sound waves move through their bodies at about the same amplitude and frequency as through water. The stony otoliths are about three times as dense as the fish's other tissues, however. When sound waves make contact with an otolith, it's not as easily set in motion as are soft tissues, so otoliths vibrate at a different rate from the tissue and fluid surrounding it. Hairlike structures in the cells beneath the otoliths bend in a particular way, sending a sound message to the brain. Many fish species also are tuned to the movements of their gas bladder in response to sound waves, which aids in hearing.

Before his retirement, Dr. Jones spent decades studying how bass use their senses for feeding, in his position of chief of fish research at Berkley. He's well known for his work on taste and smell in bass, which led to many revolutionary artificial lures. He studied bass hearing, though he didn't conduct experiments to define the sensitivity and limits of bass hearing, and he reports that few studies have examined in detail the sounds bass detect best and how their brain interprets them.

"The most important lab study was done by Dr. Don McCoy at the University of Kentucky, who was an avid angler," Jones says." He trained young largemouth bass to respond to sounds by giving them a slight electric shock to encourage them to move across a barrier. He then tested different sound frequencies to learn which ones bass could detect. He built a hearing curve based on the results.

"He found that bass have a narrow range of sound sensitivity, with a peak around 100 cycles per second, which is quite low. Bass hearing sensitivity is reduced above 200 cycles per second and sounds above 600 aren't heard. Humans, in contrast, hear quite well from 20 to 20,000 cycles per second. Bass range of hearing is common for fish that are hearing generalists. Hearing specialists, such as minnows and catfish, have greater hearing range, thanks in part to their ability to amplify sounds resonating in their gas bladder with a special skeletal structure. Because bass lack this adaptation, they hear only low-frequency sounds," Jones concludes.

Using Sound to Catch Bass

Though scientists understood characteristics of sound under water, anglers and lure designers gave it little thought until the 1950s. In-Fisherman Editor in Chief Doug Stange recalls coming across a so-called "fish call" in a mail order catalog produced by George Herter in the late 1950s. "As I recall, it was basically a small can with BBs inside, attached to a string that allowed it to be lowered into the depths," Stange says. "You activated the call by pulling the string, which shook the can. Fishing from a public dock on Lake Okoboji, I became convinced that it worked. When the bite slowed, its owner would shake it and the perch and sheepshead would start biting again."

Ever since early anglers used lures with hooks, they'd unknowingly created underwater sounds that likely resonate in the hearing realm of bass and other gamefish, as they clink against the bone, wood, or metal body of a lure. The earliest bass "plugs" of the early 20th century were carved of wood and carried no additional noisemakers. So were the earliest Rapala models that turned a page in lure evolution. Soon after, Jim Bagley created what we can call the first modern crankbaits--the Balsa B, DB2, and DB3 deep divers, and Diving Kill'r B2, designed to deflect off cover. These lures ruled the crankin' scene for many years, and still are treasured by pros and lure collectors. They also were hand-carved of solid balsa.

The development of lures with sound chambers designed to attract fish came about rather serendipitously. Famed lure designer Cotton Cordell is credited with making the first rattling lipless lure, the Cordell Hot Spot. "In the late 1960s, I designed the Hot Spot as a plastic version of the Gay Blade, a bladebait that was popular at the time," he recalled. "I placed a lead slug in the lure's nose for correct balance and increased casting distance.

"The Hot Spot was selling well, when a jobber from Mississippi called and said he'd have to return 54 dozen Hot Spots because they didn't rattle," he continued. "I told him the Hot Spot wasn't supposed to rattle. But he replied, 'They rattle if I sell 'em.' Anglers were taking Spots out of the box and rapping them on the counter at the store. They'd shake 'em to find the one where the slug had come unglued. Rattlin' crankbaits were an accident, but I soon enlarged the compartment that held the slug so all Hot Spots would rattle."

A few years later, Bill Lewis built a lure to capitalize on sound production, a lipless bait he called the Rat-L-Trap. Wes Higgins, President of Bill Lewis Lures today, recalls its origins: "Bill had been a lure designer and graphic artist. He was fan of the Heddon Bayou Boogie for catching big bass on Toledo Bend, but found that it often wouldn't run straight. He built a lipless lure with a flatter body and pointed nose and loaded shotgun pellets into the body so it would run upright. He immediately noted how loud it was, and his bass went wild for it. To promote his design, he gave Rat-L-Traps to guides on T' Bend or traded them two Traps for their favorite lure. The rest is history, as the Rat-L-Trap soared in popularity and remains a top seller 50 years later."

Success with Sound

Dr. Jones offers a likely scenario of how bass use sound in feeding: "Bass ears and lateral lines are each tuned to different frequencies," he says. "They act together to allow fish to form a composite interpretation of sounds around it." He notes potential stages in predation via sound. "The inner ears do most of the work in cluing a bass in to sounds generated more than a few body lengths away. Sounds should reach the bass directly, as solid objects can deflect sound waves. Bass hear better in deep water, as there's less background noise from the surface and sound waves travel farther. They instinctively analyze the intensity, frequency, and other aspects of the sound to determine whether it might signal food or else danger.

"It also determines distance to the object, and whether it's worth approaching. Bass don't move far to track sounds, especially if vision is limited. When a bass is very close to a target, it examines the object acoustically using the lateral line in its face, as well as its eyes. If it's suitable or it flees, it's attacked."

You can observe this behavior as bass often slowly approach potential prey and tilt their heads toward it. This movement allows the lateral lie to analyze low-frequency sounds, or vibrations, and also allows the fish to train both eyes on the object, allowing it to have depth perception. If it passes the test, the bass strikes.

A key question is, "How closely do rattling lures match the sound frequency range best detected by bass?"

Unfortunately, answers to those questions are elusive. Aside from Berkley's research lab, facilities to test this question aren't commonly available. Moreover, there doesn't seem as much to gain financially in the production of lures with appropriate auditory cues as there is with tasteful and flavorful formulas.

In the early 2000s, Dr. Hong Yan of the University of Kentucky tested the sound production of 23 common rattling lures in a concrete tank. Lures were reeled past a hydrophone, and each one's acoustic signature was amplified and recorded on a digital tape recorder. In a lab, the team analyzed the sounds on a computer and generated a power spectrum for each. This spectrum defined the relationship between the different sound frequencies produced and their loudness.

"Acousticians define the frequency that carries the higher energy level as the 'dominant frequency' of a particular spectrum," Yan wrote. "When that dominant frequency is within the hearing range of a fish species, this frequency of sound is heard most clearly. We found that only three lures we tested produced a dominant frequency below 1,000 Hz (cycles per second).

"The dominant frequencies of other lures were much higher, from 3,000 to nearly 10,000 Hz. So most rattling lures produced dominant sounds well beyond the hearing range of species they're intended to catch, including bass, walleyes, and pike. We dissected the lures found a variety of rattlers. Most had small beads that producer higher frequencies than larger beads.

"As might be expected, however, lures also produced less dominant sounds of other frequencies, but they may not be strong enough to attract fish. "Effective lures should produce the loudest sounds within the hearing range of gamefish," he concluded. "We expect important advances in the viability of lures to attract fish once manufacturers design lures based on the precepts of fish hearing."

Curious about the sounds produced by their Rat-L-Trap, Bill Lewis Lures contracted in 2002 with a company called Cetacean Research Technology of Seattle, Washington, in 2002 to compare recordings of the lure's sounds to those of a school of shad being attacked by bass. The researchers found the two sound clips generally similar in their frequency characteristics, with peak frequencies close to 4,000 cycles per second (4 kHz). This, of course, is well above the audible range of bass. Shad and Rat-L-Traps also had lesser peaks in the range of 100 to 200 Hz, within optimal hearing range, though the shad sounds were considerably louder than the lure. At 150 Hz, a peak hearing range for bass, the shad sound was 10 decibels greater than the 'Trap.

Although results of these investigations were not widely circulated or publicized, lure companies began to offer more lures that produced dominant lower-frequency sounds by using a few larger BBs or metal slugs instead of, or in addition to, many small ones. Anglers also began to recognize that especially in heavily fished waters, crankbaits that didn't rattle often were more effective than louder ones. Water clarity and activity level of bass also seemed linked to sound's effectiveness. For less active bass or those in clear-water conditions, rattles could be detrimental to success.

Several classic crankbaits produce sounds that seem to be of low-frequency sound, such as the Bomber 7A and Bandit 200, due to a single large ball that contacts the sides as it's retrieved. Booyah was one of the first to add a low-frequency lipless lure, the One Knocker Spot, shaped like the Booyah Hard Knocker (formerly XCalibur Xr75), but with a single large tungsten rattler that produces a loud and steady thump as it's retrieved. It's offered in 1/4-, 1/2-, and 3/4-ounce sizes and 18 finishes. It's proven to be a popular addition.

Rapala engineers designed the Clackin' Rap and Clackin' Crank with a unique rattle chamber based on a pair of metal discs inserts on each side of the lure that clack against the plastic body as the lure rocks during the retrieve. Although they garnered praise as excellent fish-catchers, they were competing with several other new Rapala models so they didn't get as much promotional drive as they might otherwise have. In any case, they were discontinued about two years ago due to lagging sales. Rapala's DT series, built with a small and subtle rattle chamber encased in the balsa body, have remained extremely popular

Strike King recently added the Red Eyed Shad Tungsten 2-Tap to their arsenal, using a tungsten bead to create a low-frequency double-tapping sound that's proven highly effective. It complements the standard Red Eye Shad, which has what sounds to humans like a higher-pitched sound. It's available in 1/2- and 3/4-ounee sizes. A Texas angler reportedly boated a Texas ShareLunker over 13 pounds on one this spring.

* In-Fisherman Field Editor Steve Quinn is an authority on black bass and has written for In-Fisherman publications for decades.

Sound Choices

Appealing sounds can summon bass or raise their interest in feeding, provided they're within audible range. While we await fuller analyses and descriptions of lure sound and bass perception, it often pays to experiment with rattlebaits and crankbaits that range from noiseless (except for rattling hooks and cover contact] to those producing loud sounds of various frequencies.

Bandit 200--classic crank with lwo-frequency knock

Rapala Clackin' Rap

Rapala DT20--balsa bait with subtle rattle chamber

Strike King 6XD--mix of large and small rattles in chamber, offering a range of frequencies

Jackall TN60--no rattles

Bill Lewis Rat-L-Tap--favorite for 50 years with loud rattles of high-end frequencies

Berkley Digger 8.5--loud rattle of intermediate frequencies

Custom flat crankbait--no rattles

Bagley Rattlin' Kill'r B--In addition to many balsa baits, Bagley now offers rattling models with ABS-resin bodies with internal sound chambers that produce low-frequency rattles.

Caption: Hearing & Lateral Line In Bass
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Author:Quinn, Steve
Publication:In-Fisherman
Date:Jun 1, 2019
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