How Water Temperatures Affect Largemouth Bass Behavior and Metabolism

Water temperature is one of the most significant factors to rely on when trying to locate and catch largemouth bass. As water temperature changes throughout the year, so does fish behavior and metabolism. Learning to identify how lakes change and how largemouth adapt to these changes can improve your success on any body of water.

Fishing for largemouth bass during the hot summer months is often frustrating because warm water temperatures can make finding and catching fish difficult. Periods of seasonal transition, however, are typically excellent times to track largemouth bass based on water temperature. One such time is early fall when air temperatures begin to dip into the 70° F range. In ponds and lakes, this initial cool-down period is a precursor to fall turnover. Pre-turnover water temperatures instinctively cue fish that winter is coming and feeding activity generally increases.

What is fall turnover? It’s a process that breaks down the stratification, or layering, of warm surface waters above cool or cold deeper waters that occurs in lakes during the summer. During the summer, mixing only occurs in the uppermost layer of water. Most folks that have been swimming in a farm pond during the summer have noticed this stratification…your upper body feels nice and warm, but your feet are ice cold. Fall turnover occurs as surface waters cool, become more dense than underlying layers, and sink, thereby pushing the underlying water layers to the surface. This mixing action occurs until all water is the same temperature (isothermal) from surface to bottom.

Fall turnover of a stratified lake

In most lakes and reservoirs, as water mixes from surface to bottom, it is likely to become less clear and odorous from gases trapped in the bottom mud. Dark, dead vegetation is another clue that fall turnover has occurred.

The body temperature of a largemouth bass is the same as the water where it lives. As a result, its metabolism and body chemistry change as water temperature changes. An abrupt decrease or increase in temperature of 8 degrees or more can cause internal chemical imbalances in fish. It’s important to realize that when largemouth bass experience changes in temperature, they may become inactive until their bodies can reach equilibrium at a new temperature. It may take largemouth bass several days to recover from a decline in temperature, whereas they can recuperate from an increase in temperature in only a few hours. Therefore, cold fronts have a greater impact on fishing than warm fronts.

Largemouth bass will instinctively move to warmer water when the water temperature is below 76° F and to colder water when above 86° F. A largemouth bass can detect changes in water temperature less than one half of a degree using its lateral line. In spite of this, bass will not normally search for locations that offer optimum temperatures if all of their basic needs are being met. Even though they are most likely to move to feed or avoid life-threatening conditions, no single factor is dominant enough to force bass to move away from satisfactory conditions in an effort to achieve optimum conditions.

Cooler water temperatures slow the metabolism of largemouth bass, which causes them to limit movement and eat less. Even though the metabolism of largemouth bass slows in cooler water, this does not mean that they cannot swim fast or aggressively strike a passing lure. However, smaller prey such as aquatic insects typically offer less resistance to capture, take less energy to digest, and are often targeted by largemouth bass when the water cools to around 50° F. Even at this temperature it may take between 4 and 7 days for a largemouth bass to digest a single meal. This strategy of consuming small prey items allows largemouth bass to expend less energy capturing and digesting food, which enables them to be more efficient in cold water.

At 39° F, which would occur mostly in northern latitudes where ice cover is possible, it is theorized that largemouth bass may only feed a couple of times per month during the winter, and each meal takes between 14 and 17 days to digest. Therefore, locations that consistently produce notable catches in late fall or early winter are likely to be where large aggregations of largemouth bass can be found until they “migrate” to spawning grounds in the spring. However, only a few will be caught on a daily basis due to their slow metabolic processes and feeding behavior in cold water.

Fish must use the energy from a single meal to meet several needs. Carnivorous fish, like largemouth bass, have an energy budget that differs from herbivorous fish such as grass carp. Approximately 20% of the energy gained from what largemouth bass eat is discarded as waste, 15% is used for activity or movement costs, 14% is applied for digestion, 7% is used for standard metabolic processes, and the remaining energy is split between growth and reproduction.

One thing you must keep in mind when fishing transitional periods (drastic or seasonal changes in water temperature) is that largemouth bass are adapting to climatic changes. Accordingly, anglers must also adapt their fishing patterns and techniques if they expect to consistently find and catch largemouth bass.

It is key to pay careful attention to aquatic vegetation during the fall to winter transition in lakes. Observing the state of vegetation, whether heavy or sparse, green or brown, or deep versus shallow, is helpful in locating and catching largemouth bass. For example, aquatic plants become sparse in shallow water, which will cause largemouth bass to seek vegetation in deeper water on protected breaks and on inside bends near large flats. As winter approaches, all vegetation in the shallow portion of the lake has begun to turn brown and die. Occasionally, largemouth bass will cruise these areas on warm, sunny days, but, more often they are forced to hold on steeper drop-offs among rocks or stumps.

Another important factor to consider is wind direction and time of day. During the pre-turnover period, when largemouth bass tend to school and feed heavily on baitfish, anglers often target the windy banks because baitfish tend to be concentrated in these areas. However, on cool days in late fall or early winter, this may not be the best strategy. When there is a little “chop” on the water, light, and thus heat, do not penetrate the water’s surface to any considerable depth. As a result, areas affected by wind may become less attractive to largemouth bass. In areas that are as flat as glass on cool days, light, and subsequently heat, can stimulate inactive fish to feed more readily. Largemouth bass are typically more active during the middle or warmest part of the day in fall and winter. As a result, you may have success fishing for largemouth bass on large flats or in shallow coves adjacent to deeper water during the warmest part of most autumn days or during sudden warm spells.

As discussed above, water temperature directly affects the bodily functions and behavior of largemouth bass in many ways. When water temperature is actively changing, bass will adapt accordingly. For consistent fishing success, therefore, it is vital that anglers understand how and why bass behave as they do at various temperatures. It’s also very important to know, not only the water temperature at the time you are fishing, but also the temperature trend in the days preceding your trip. Doing your homework on water temperature definitely increases fishing success.

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