July 14, 2020
When examining the feeding and other behaviors of black bass, we first acknowledge their reliance on vision as the primary sense. These members of the sunfish clan are designed through the amazing powers of evolution to be shallow-water, daytime predators in the smaller waters where they were originally found. One clue is their difficulty feeding in murky conditions or in darkness. Laboratory tests find that they can still consume prey, but with far less efficiency than in well lit conditions.
Bass have been by far the most successful freshwater predator across the North American continent. Largemouth bass have expanded their ranges from southern river backwaters and clear lakes to turbid impoundments, tiny ponds, brackish estuaries, canals, and desert reservoirs. From their roots in the southeastern U.S., they’re now found in more than 50 other countries. Smallmouths are more particular in their habitat requirements than their cousins, but still represent a very versatile predator that uses many sensory and behavior skills to thrive far from its midwestern roots.
Can You Hear Me Now?
Beyond vision, alternate senses have enabled bass to thrive in these varied environments. First among these is their sense of hearing, which was neglected by human predators for eons, simply because fish did not possess obvious ears. But they have ears that are finely developed for underwater operations. They’re similar in many ways to those of humans and terrestrial animals, with a system of connecting ducts, sensory cells, and stony inclusions called otoliths, but they operate with a much narrower range of frequencies. While we detect sounds between about 20 and 20,000 cycles per second (Hertz), bass hear sounds from about 10 to 600 Hertz, with peak hearing sensitivity around 100, as determined by extensive lab experiments performed by Dr. Don McCoy at the University of Kentucky.
Until the late 1960s, nearly all lures were built of metal or wood and relied on visual attraction and action to fool fish. In the meantime, scientists in the fields of physics and biology had revealed how sound was capable of long-distance transmission under water and how aquatic creatures used it to communicate, find prey, and avoid danger.
For the fishing industry, breakthroughs in using sound to catch fish began in the late 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. “As I recall,” Stange says, “it was basically a small can with BBs inside, attached to a string so you could lower it into the water. You activated it by pulling the string, which shook the BBs. Fishing from a pubic dock on Lake Okoboji in Iowa, I became convinced that it worked. When the bite slowed, its owner would shake it and the perch and sheepshead would start biting again.”
Development of the Cordell Hot Spot and Bill Lewis Rat-L-Trap lipless lures inaugurated the era of rattling baits, and anglers bought them up as fast as they could be produced. And many lipless rattlers remain top sellers 50 years later, due to their sound production, flash, and the lower-frequency vibrations they also produced.
Lures that present a spectrum of sound within the hearing range of bass often produce outstanding catches, especially when bass are grouped and in a feeding mood. I’ve experienced this many times, when noisy, erratic lures outproduce more subtle options. But there can be too much of a good thing. After initial success with noisy lures, bass sometimes seem to become conditioned to them and respond less positively.
Waters facing intense fishing pressure are most prone to these effects. You may have noted it after using a favorite lipless lure regularly on a small body of water. This effect has been clearly demonstrated in a laboratory setting, notably at Berkley’s science facility in Spirit Lake, Iowa. Dr. Keith Jones, head fish behaviorist there, found that naive bass living in a rather sterile environment (a giant tank), quickly learned to ignore hookless hardbaits towed through their territory. A few strikes that didn’t reward them with food were enough to change their attitude, even without being hooked. Many field studies have found that fishing pressure reduces catch rates of bass, even when they’re all released. Caught and released bass tend to be less eager to bite again, though there is a remarkable range in catchability among members of a bass population.
Fishing experiences yield only observational evidence, not scientific data, yet they can serve as the basis for human learning about the behavior of bass and how they can be caught in various situations. Rick Clunn’s victory on the Arkansas River at the 1984 Bassmaster Classic serves as a notable early example of the effects of sound on the catchability of bass.
He’d found a huge group of bass along submerged ledges and had been catching big limits with a Bomber 6A, a crankbait that produces a distinct low-frequency knocking sound. On the last morning of the tournament, three passes along the most productive structures produced not a bite. Avoiding panic, Clunn switched to a silent lure, a Rapala #7 Shad Rap. The lure switch worked like a light switch and he boated 28 pounds to triumph easily. According to Clunn, he’d switched lures to offer a more subtle action. “I’d initially thought the difference was in the more subtle wiggle of the Shad Rap,” he recalled. “But in the years since, I’ve confirmed to myself that on many occasions lure sound production is the key factor in getting bass to bite. When bass spurn noisy baits, offer them something that produces minimal sound.”
Veteran Mark Davis had a similar experience on the last day of the 1995 Bassmaster Classic at High Rock Lake, North Carolina. “I had to switch to a silent lure when they quit biting the rattling lure that had been working well,” he says. “I think sound production, or lack of it, is critical in selecting lures for a situation.”
Under water, movement of water, like that produced by nearby fish, currents, wind, or human activity is considered an acoustic phenomenon, as the resulting compression waves emanate from the source and move outward. This physical characteristic of sound led to evolution of a lateral-line system in fish and aquatic amphibians. This sensory organ allows them to detect and 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. It’s easily observed on the sides of bass and other fish as a series of pores extending from the head to the tail.
Lab studies published in 2000 by John New and in 2012 by Jayne Gardner and Philip Motta showed that captive bass could feed successfully when blinded. New’s studies took place in the total absence of light detectable by bass, where infrared illumination (invisible to fishes in the sunfish family) allowed the scientists to watch bass feeding. Instead of the directed, mouth-open charges that characterized feeding in daylight, some largemouths slowly turned toward a baitfish and approached it, followed by a rapid expansion of the mouth to accomplish suction feeding. Others hunkered near bottom until a preyfish approached close enough to be engulfed by this vacuuming strike, which is effective only in a range of a few inches. These bass had to feed using only their lateral-line sense, which allowed them to be successful in aquarium surroundings. I’ve caught a couple of double-blind bass in my 60 years of fishing and they’ve been severely emaciated. We know from other studies that without sight or a lateral-line capability, bass cannot feed at all. Olfaction and a sense of taste are important senses for bass feeding, but not for finding and capturing prey.
Experts in fish sensory mechanisms have separated underwater sound into far-field effects, which are detected with the inner ear, and near-field effects, which the lateral line perceives and interprets. As the term suggests, fish must be close to the source to detect near-field sound, probably within several feet in the case of bass. It’s the mechanism by with bass approach a sinker that cascades into a patch of vegetation where a fish is holding. This water disturbance can provoke a feeding response from a nearby bass. Bass rely on this sense particularly when feeding at night or when waters are murky enough to limit visual range to a few feet, not an uncommon situation in silty reservoirs or fertile ponds.
Recent research has pointed out that fish species detect and can follow the trail of fish that have just passed, perhaps identifying its species and size, and whether it’s weak or wounded, which would make it a prime target. As fish swim, they create hydrodynamic vortices that can be seen by adding dye to a fish tank.
This detection comes via the lateral line, and provides a advantage for anglers. Lures create their own trails though the water, some more lifelike than others. At In-Fisherman, we’ve often hypothesized that the reason predators respond so strongly to swimbaits is because the low-frequency trails left in their wake. We often see bass, walleyes, and pike with the entire swimbait within their mouths. They didn’t feel the need to nip or bump to believe it was the real deal, but unhesitatingly inhaled it.
Other lures produce low-frequency vibrations that bass detect at close range, which can convince them to bite—the subtle wiggle of a craw’s pincers on the back of a jig, as an angler gives it a subtle shake; the deadly pause with a jerkbait or topwater lure that causes a following fish to commit to striking; or the pulse of a big Colorado-blade spinnerbait helicoptering down a breakline.
These lures can be especially effective when bass rely less on their sense of sight, more on other senses, notably the lateral line. They must be close to the lure to begin with, then may approach the object of interest even further, using the lateral line to analyze the vibrations. A lure can either pass or fail the test at this point, and we anglers have no idea how many big bass have come close to striking, but refrained, due to some warning sign.
*In-Fisherman Field Editor Steve Quinn has long contributed articles connecting fishery science topics with applications to fishing.