The Effects of Cold Fronts on Bass
April 04, 2018
I admit my past skepticism about the effects of cold fronts on bass. Some of my hesitancy to buy into the mother of all excuses for not catching bass is that I've enjoyed some memorable catches under post-cold-front conditions, even classic conditions with a high barometer, bright blue sky, sharply colder temperatures, and a strong north or northwest wind. My skepticism also was fueled by poor catches under what my highly skilled fishing partners and I considered "ideal" conditions. But my largest reasoning for questioning the purported adverse effect of cold fronts is the lack a biological explanation for it.
Yet anglers like guides and tournament pros who have to fish and catch fish to make a living, regardless of weather conditions, generally insist that cold fronts affect bass. With data like that, it's hard to deny the curse of the cold front. What allayed my skepticism about its effects on bass fishing was that the anglers I interviewed for this article all agreed that cold fronts don't always shut down the bite.
"The effect of a cold front varies with seasons, and may even turn bass on in fall," says Bassmaster Elite pro and consummate power fisherman Ish Monroe of California. "The bite tends to drop off, and I have to adjust tactics about half the time after a cold front," says In-Fisherman Field Editor Ned Kehde, a perpetual practicioner of finesse fishing. "I think eight or nine out of ten cold fronts change the bite unless you are fishing in Florida—then it's 10 out of 10 times," notes Bassmaster Elite pro Mike Iaconelli, a versatile angler with a leaning toward finesse. "And it's not always the first day after frontal passage," Iaconelli adds. "Sometimes the second day is the toughest." Iaconelli echoed Monroe's seasonal perspective, indicating a fall cold front often turns on the smallmouth bite. Variation is typical in biology, and some degree of inconsistency in response to a weather condition—just one of the many factors that influence how fish behave—makes it easier for me to buy into the curse of the cold front.
Various explanations for adverse effects of cold fronts have been offered from "bright sun hurts bass' eyes" to high pressure "makes bass uncomfortable" or "hurts their inner ear." One innovative thinker professed that bass detect change in barometric pressure via the lateral line. The lateral line does detect changes in water movement, a "pressure" of sorts, but it does not detect static pressure as occurs with atmospheric pressure. Others have proposed food web effects: Bass shut down when their food moves to where it is less accessible. Few successful anglers would argue that bass often hold near food, but attributing the effect of a cold front to the bass' prey, or the food that the prey consumes, is simply passing the buck down the food chain.
The Biology of Cold Fronts
The very few studies (none on black bass) that have considered the effects of cold fronts or climatic variables associated with them on fish—falling temperature, rising barometric pressure, clear sky, and wind—are far from compelling. Researchers at Bemidji State University found no effect of barometric pressure on food consumption of yellow perch in laboratory experiments. Barometric pressure was one of several variables affecting depth occupied by sauger in Melvern Lake, Kansas, but it did not affect movement rate. In Brant Lake, South Dakota, movement rate of black crappies was positively related to barometric pressure but not affected by temperature, light penetration, cloud cover, wind direction, or wind speed. Here, black crappies moved more during high barometric pressure, while anglers often feel bass move less and are tighter to cover under those conditions.
Lacking sufficient information to predict how bass respond to cold-front conditions, let's look at each of the weather variables that change with the passage of a cold front and answer two questions. First, can the bass detect the environmental changes? Second, is the information biologically meaningful?
Water Temperature—Temperature has profound effects on bass. It's one of the triggers for the spawning cycle and, via metabolism, affects feeding frequency and swimming ability. All fish species have preferred temperature ranges, so temperature also affects location and movement. Clearly, bass detect and respond to temperature, so it's a good candidate as an effective environmental cue.
Air temperature often plummets after a cold front, but water temperature, not air temperature, affects fish. Water has a high heat capacity; it takes far more thermal energy to change water temperature by one degree than air temperature, and air loses thermal energy far faster than water. Thus, large changes in air temperature result in minor changes in water temperature. I have little doubt that the temp gauge on your boat may read as much as 8°F to 10°F cooler the morning after a front passes, but it's reading surface temperature, and that's not where bass live. The density of water is inversely related to temperature, so cool, dense water won't float on warmer, less dense water.
The temperature drop you attribute to cold air is actually the surface water cooling to the temperature of slightly deeper water. Only in expansive areas of extremely shallow water might the temperature where bass live change more than a degree or two after a couple days of chilly weather. Further, water temperature varies both vertically and horizontally throughout water bodies on any given day, so temperature change is status quo for them. Minor temperature changes associated with a cold front don't seem biologically meaningful.
Bluebird Skies—Brilliant blue skies result from cleaning particulates out of the air if rain accompanies the passing of the front and from the low humidity that allows more UV light to pass through the atmosphere. Obviously bass can detect light, but it's a myth that "light hurts bass' eyes." If it did, chasing schools of baitfish to the surface or spawning in shallow water would be a painful experience and deter bass from feeding, procreation, and parenting in shallow water. Furthermore, bass are accustomed to variation in light intensity—light intensity changes from dawn to midday to dusk every day. Thus, bright light is not biologically meaningful.
Wind—Do bass care about wind? Fish in shallow water on the windward shore may be affected when waves crash into their habitat, but it shouldn't affect them elsewhere in the lake. Wind disturbs the surface and reduces light penetration and can generate slight currents in a lake. These currents can concentrate plankton on the windward shore that, via the food chain, attracts predators.
And current is known to turn on the bite in hydropower reservoirs. These effects of wind are generally considered desirable by anglers. Bass possibly can detect wind by sensing current via the lateral line system. But can they detect wind speed and direction? Likely not, because wind causes surface water to move with wind direction, but subsurface currents move in the opposite direction, and the amount of wind-generated current is as much an effect of lake size and how long the wind has been blowing as wind velocity.
Thus, wind is not a biologically meaningful factor, although it makes fishing difficult, sometimes even dangerous on big waters.
Barometric Pressure—Except for infrequent events like hurricanes and typhoons, barometric pressure usually ranges from about 990 millibars, or 29.2 inches of mercury, to 1030 millibars, or 30.4 inches of mercury. Anyway you report it, the result is the same—a rather severe change in barometric pressure, one that occurs when the barometer changes from very low to very high, is a change of only 4 percent.
Can fish detect this? Any fish with a swim bladder potentially has a built-in pressure-detecting organ. And sharks, which lack swim bladders, have sensory cells that detect changes in water pressure. Bass probably can detect small pressure changes.
Water is heavy, and atmospheric pressure increases one atmosphere for every 10-meter—approximately 33 feet—increase in depth. Doing the math, the 4-percent increase in pressure that a fish would experience with the passage of a major cold front equates to the same pressure change a fish would experience moving about 16 inches deeper in the water column, a fraction of the depth change bass commonly undertake in their daily movements. It's a safe bet that the "discomfort factor," which I've read in more than one article, isn't what changes fish behavior.
Based on what's known and can be inferred from fish biology and the limited behavioral studies, there's no biological explanation for cold fronts affecting bass behavior. And I don't foresee a great expansion of knowledge because the effects of cold fronts, a non-destructive and totally natural phenomenon, have little to do with the conservation or management of bass or any other fish species.
Coping with Cold Fronts
Nevertheless, the curse of the cold front appears to be more than myth. It's important for anglers to remember that the bass bite doesn't always die after a cold front. Monroe offers valuable advice: "Don't assume the bite will change for the worse; always give a producing pattern a try before giving up on it." And Kehde offers a meaningful thought: "I don't try to prove causality; I just note how, when, and where I catch each bass and adjust." Tips from Iaconelli, Kehde, and Monroe provide ideas to help you adjust to cold fronts.
Monroe's Approach—Monroe, who rarely deviates from power-fishing, uses a seasonal approach. In fall, a cold front can be a good thing, especially the first cold front after the heat of summer has waned. In spring, however, a cold front often pushes bass off the beds. But regardless of season, adjustments often are in order.
Around the spawn, Monroe advises slowing down and fishing Texas-rigged softbaits in thick cover. In summer he relies heavily on jigs and deep-diving crankbaits in prime conditions. After a front, he fishes where he'd found active fish but counts on a morning or evening topwater bite.
Shad move into coves in fall and bass often follow. Monroe has found that after a cold front, bass remain aggressive there. He recommends crankbaits, spinnerbaits, or jerkbaits. In winter, he stays where he'd been catching bass before the front, but slows way down.
Iaconelli's Approach—Iaconelli's cure for post-frontal bass is to shift into deeper water or thicker cover. "Bass don't move far after a front, but they usually move," he says. "If I've been catching them shallow along a bank, such as on a breakline of a flat that's 10 to 12 feet deep before the front, I often find they've backed out deeper after its passage." He moves off the break and fishes a deeper diving crankbait, jig, or a Carolina rig. Plan B is to look for thicker forms of cover, whether it's vegetation or wood, near where he's been catching fish. "Change your approach from covering water to slowing down and probing into cover. Pick it apart, and soak the lure. A small, Texas-rigged softbait is an effective presentation."
If that approach doesn't pan out, he looks for suspended fish, the hardest fish to catch. When he marks bass and baitfish, he tries to tempt bites with finesse swimbaits like a small Berkley PowerBait Ripple Shad or Havoc Beat Shad, or a Power Grub on a 1/8- or 3/16-ounce head, or else a finesse hardbait, like a spybait, jerkbait, or small crankbait like a #5 or #7 Rapala Shad Rap.
Kehde's Tactics—Kehde deviates little from his finesse approach with a mushroom jig/small softbait, but he does change the presentation if the bite is off (catch rate of less than five bass per hour) after a front. On a typical day, he fishes a variety of shallow (1- to 8-foot deep) habitats and rotates through several softbait dressings—Z-Man ZinkerZ, Finesse WormZ, Finesse ShadZ, or a Yamamoto Shad Shape Worm on a 1/32- to 3/32-ounce Gopher Tackle Mushroom Head Jig. His usual presentation is a swim-glide-shake retrieve.
After a cold front and if the usual presentations aren't working, he stays shallow and continues to move among different habitats. He uses the same drag-and-shake with a cut-down section of a Z-Man Hula StickZ or a 2.5 or 2.75-inch TubeZ on a 1/16-ounce mushroom jig rigged internally and retrieved with a slight hop. If bites are still scarce, he begins experimenting with color, switching from green pumpkin baits on a red jig to junebug or pearl-color softbaits on chartreuse jigheads.
*Dr. Hal Schramm, Counce, Tennessee, is an avid angler, fishery biologist, and freelance writer. He often contributes to In-Fisherman publications.