The New Bass Science

by John Weiss

Understand how a lake's oxygen and pH levels determine where bass must be and catching them becomes infinitely easier!

It was in 1974 that an Austin, Texas scientist by the name of Dr. Martin Venneman, who also happened to be a devoted fisherman, decided to analyze the watery world of bass. Using sophisticated lab equipment on loan from Texas A & M University, Venneman studied numerous bodies of water and made a startling discovery. "At any given time," Venneman reported, "from 50 to 80 percent of the water in any lake does not contain enough oxygen to support fish life."

The explosion you heard was a revolution in bass fishing that has rippled from border to border and coast to coast as anglers nowadays use modern science to unlock many of bassdom's previously guarded secrets. And many innovative companies are helping them by providing scaled-down, economical devices that are enabling them to enjoy far more fish-catching success than ever.

It's important to emphasize that oxygen-monitoring equipment and pH meters (to be discussed shortly) will not guarantee that you will consistently be able to find or catch bass. What they do guarantee is that you will not waste time fishing where no fish can possibly survive. In other words, oxygen and pH evaluation are two easy-to-learn techniques the seasoned angler can use to systematically eliminate barren or unproductive water. All efforts may then be concentrated in those areas almost certain to contain large numbers of fish.

It should also be mentioned that bass living in rivers and streams are seldom influenced by changing oxygen or pH levels. The ever-present current in such flowing waters generally makes any unfavorable changes in the water chemistry so short-lived that they have no effect upon the bass and do not force them to radically alter their habits or move to other areas.

Oxygen and pH evaluation is most useful to anglers on larger lakes and reservoirs where miles of shoreline twist and turn to form numerous channels, bays, coves and other such places which may be subject to wide variations in water temperature, light penetration and, most important, oxygen and pH levels.

They Gotta Breathe!

All species of fish must have enough dissolved oxygen in the water around them in order to live. Although bass are quite tolerant with regard to other environmental variables, their requirement for minimum oxygen levels is absolute. There can be no compromise or adaptation. If oxygen levels are too high, or too low, they must either move out of the area altogether, or perish!

Survivable oxygen levels for bass range from 5 to 13 parts per million (ppm), though they highly prefer and will seek out waters with 9 to 12 ppm oxygen. If the oxygen level falls below 3 ppm, the fish will die of asphyxiation. And if they remain in areas with more than 13 ppm, they will experience oxygen poisoning.

The effects of oxygen depletion or oversaturation are most likely to be noticed in the late summer and fall months, and though they may last only a day or two, they also may last several weeks. This is why anglers should frequently take oxygen level readings in those lake sections they fish most regularly, especially if they are having difficulty finding and catching bass.

Most oxygen meters available today are small, battery-operated, hand-held devices that cost less than $50 and are available through mail-order houses such as Bass Pro Shops and Cabela's. They have an oxygen-sensing probe attached to a metered line that is lowered into the water to various depths. When a button is pushed, a needle gauge registers the parts per million of oxygen in that area.

To reap the greatest benefit from an oxygen monitor, you should spend a little time, at the very beginning of the first day on the water, determining oxygen levels in various portions of the lake or reservoir. Motor back and forth across the lake, taking oxygen readings here and there and jotting down the numbers on your contour map. Now you're ready to begin fishing the types of depths, bottom structure and cover which bass in that area are likely to be using at that particular time of year. You've completely eliminated from consideration those areas found to be incapable of supporting fish life, regardless of how "bassy" they may look.

On subsequent days on the water, you need only quickly reconfirm the oxygen levels at your favorite fishing locations. If something has happened to radically change the oxygen level (most often an abrupt change in wind direction or barometric pressure), you can be pretty sure that the bass have left the area, and so should you.

Try a pH Monitor

The pH of a solution is a measure of its acidity or alkalinity. The pH scale runs from 0 to 14, with a measurement of 7 considered neutral; anything lower than 7 is acidic and anything higher than 7 is alkaline, or basic. 

Like all animals, fish must maintain a certain chemical balance in their blood and body fluids if they are to survive. Since the pH of their blood is slightly alkaline (7.6), it is not surprising that bass seek out water with approximately the same pH. When the water pH is near this value, bass are best able to withstand stress and utilize the oxygen in the water properly. This is not to say bass will travel far distances to find an ideal pH; the species are very adaptable and can survive in water with a pH ranging from 6.7 to 9.6. However, given any choice, if there is water within their immediate region that has a pH of 7.5 to 7.9, that is where bass will be.

It was in 1979 that Dr. Loren Hill, then chairman of the Zoology Department at the University of Oklahoma, developed the first pH meter for fishermen. Other companies have since introduced their own devices, which operate in basically the same manner as oxygen meters and are comparably priced.

Most advanced anglers use an oxygen meter first, to locate themselves in a specific lake region where bass have concentrated. However, since the depth range in a given area may be from 1 foot (at the shoreline) to 100 feet deep or more far offshore, the angler still is faced with an enormous amount of water to explore. A pH meter dramatically reduces this time if it is used to determine a so-called pH profile.

This procedure entails lowering the pH meter's probe into the water, taking a reading at the surface and then subsequent readings at one-foot intervals all the way to the bottom. After recording these values on a notepad, you'll discover a pH breakline at some particular depth---that is, a point where the pH changes rapidly.

For example, readings may fluctuate back and forth by one-tenth of a unit, and then suddenly, at some specific depth, you'll note a full one-unit change in pH. This swing may not seem significant, but in actuality it is. The pH scale is logarithmic, so pH 8 is ten times more alkaline than pH 7, and pH 9 is 100 times more alkaline than pH 7.

The value of understanding this is that Dr. Hill learned that in any lake the pH breakline is the depth at which a majority of bass congregate and are the most active.

What a boon to anglers! With an oxygen meter, any fisherman can easily and quickly learn what regions of the lake are holding the greatest numbers of bass. And, in refining his search, his pH meter will tell him the depth the fish are at. Now all he has to do is look for an abrupt change in bottom contour at that depth, or cover bass like such as weeds or stumps at that depth, and begin catching fish. 

Some may disdain the use of the new bass science, claiming it eliminates the romanticism and mystery of randomly chancing upon a fish here and a fish here. But personally, rather than spend most of my day "fishing," I'd rather spend it "catching."