October 27, 2016
The warm-to-cold-weather transition period is a frustrating time for many black bass anglers. One day, bass are deep; the next, they’re on top. Where fish nailed anything yesterday, they refuse everything today. Just as the seasons are changing, so are the daily routines of largemouth, smallmouth and spotted bass.
You’ll often hear this referred to as “turnover time” because the water is “turning over” as the cooling surface layer sinks and warmer bottom water is pushed upward. Some anglers write this off as a terrible time to fish. But turnover needn’t be the nemesis many perceive it to be. Bass fans can actually benefit from this phenomenon if they understand it.
What is turnover?
During summer, many lakes stratify into three distinct layers. These lakes have a layer of cold, poorly oxygenated water on the bottom, and a layer of warm, moderately oxygenated water on top. Because cold water is heavier than warm water (to a certain degree), the warmer water stays on top and colder water sinks to the bottom. In between lies a layer of cool, oxygen-rich water called the “thermocline.” Summer bass are usually found in or near the thermocline because that layer best satisfies their needs for oxygen and water temperature.
In late summer, fall or early winter (the exact time depends largely on the latitude in which the lake lies), cool weather begins lowering the surface water temperature. As the upper layer cools, it becomes heavier and sinks. This action forces the warmer, lighter water below back to the surface. This water subsequently is cooled, just as the previous surface layer was, and descends as it cools. This mixing or “turnover” continues for several weeks until the thermocline disappears and all water in the lake is roughly the same temperature. This mixing effect also replenishes the oxygen in deep water.
The end result is that fish formerly restricted to narrow bands of acceptable oxygen and temperature levels are no longer limited in their movements. Bass that once were barred from dropping into the coolest depths because of low oxygen levels now may roam freely to much deeper water. Likewise, where once fish could not spend extended periods in extreme shallows due to high temperatures and low oxygen levels, after turnover even these areas are acceptable. Bass may now be found deep, shallow or anywhere in between.
Technically, turnover continues until the surface water temperature drops below 39 degrees F. Water is heaviest at this temperature and sinks to the bottom. Cooler water “floats” on top. Therefore, our lakes freeze from the top down, rather than from the bottom up. And this represents the annual end of the turnover process.
How do I know when a lake is “turning over”?
The time of year when turnover occurs varies by latitude. While anglers in cooler areas may begin turnover strategies in September, warmer regions may not have turnover until January.
On many lakes, the turnover is clearly visible. A change in water color is evident as circulating water brings up bottom debris. The water may take on a milky or brownish tint and smell like rotten eggs or decaying vegetation.
Turnover in some lakes is invisible and therefore confusing even to those familiar with the phenomenon. In these waters, the only indication turnover is occurring may be distinct changes in bass behavior after a few weeks of cool weather. For instance, bass caught on deep humps one week may be ambushing baitfish near shorelines the next.
Some waters don’t experience turnover because they don’t stratify in summer. Rivers are a case in point. So are many large, shallow, windswept lakes and some reservoirs with lock-and-dam facilities or hydroelectric generators. In extreme southern areas, south Florida for example, temperatures may not drop low enough for turnover to occur.
What problems are associated with turnover fishing?
The biggest problem most anglers face is pinpointing fish. In summer, most bass were found in or near the thermocline. Shallow-water action might be good during cool, low-light periods, but you could be certain no bass would be caught in the “dead zone” below the thermocline.
Fall turnover drastically changes all this. With acceptable levels of oxygen from top to bottom, and no discernible temperature change from the shallowest shallows to the deepest depths, bass can be almost anywhere.
Can I overcome this problem?
Yes. The secret to turnover success is realizing that bass still concentrate in areas that provide the most comfortable living conditions and then learning to identify those areas. Theoretically, conditions are now such that bass can live anywhere within the lake. In actuality, factors such as oxygen content, light penetration and food availability still greatly influence a bass’s choice of living quarters.
Consider, for example, that all the debris and poorly oxygenated water being pushed upward from the lake bed when turnover begins temporarily “trashes” the whole system. Bass respond by seeking areas with good quality water. To find them, anglers should do likewise. An easy way to do this is to work tributaries bringing fresh water into the lake. Another way is to look for areas where turnover has not begun. On some large lakes, different arms of the lake turn over at different times, and anglers can concentrate their efforts in areas that aren’t visibly affected.
When turnover causes excessive amounts of decaying debris to circulate in the water column, sudden significant drops in the oxygen level can result. When this happens, bass must find oxygenated water immediately. They frequently solve the problem by going directly to the nearest source, which is surface aeration from wind and waves. Consequently, windswept shorelines in fairly shallow cover may be productive bassing spots.
During the final few weeks of turnover, as the water starts to clear, bass often concentrate on vertical structure. This is some type of bottom feature that offers great depth variance with little or no horizontal movement necessary. Good examples are bluff banks, bridge pilings and fast-dropping slopes along creek and river channels. In such places, bass can alter their depth per prevailing light penetration and other factors by merely moving up or down the structures as conditions dictate.
Because bass orienting to vertical structure can be anywhere between the bottom and the surface, pinpointing them may require extra effort. Begin by thoroughly fishing different depths until fish are located. If the water is still discolored, light penetration will be restricted, and bass will move shallower. Thus, the angler should begin by fishing shallow reaches first. As the water clears, however, bright sunlight will drive most bass into the depths or under heavy cover, especially green vegetation. In this situation, fish first around deeper hideouts or weed beds.
The key is to efficiently check all depths until a bass is caught. Then work that depth thoroughly for additional fish. When you’ve established the level where fish are holding, then move to other vertical structures and work the same depth. Chances are good you’ll encounter another school of bass at some point along the way.
Is there anything else I should know?
Be patient and persistent. Turnover forces fish to roam; thus, anglers must also be willing to move frequently, forsaking likely looking spots or those that produced yesterday. If the tactics covered here don’t produce bass, improvise another strategy and keep trying.
The turnover transition is jolting for both fish and fishermen. Bass find their once-secure world literally turned over on them. Bass anglers find their quarry more unpredictable than ever. Overcoming this seasonal nemesis will require all the skill, knowledge and patience you can muster. But when you finally zero in on a big school of hefty autumn bass, you’re sure to agree that the rewards make the extra effort worthwhile.