Fish Science
How Bass Change With Temperature

Photo: Berkley Here's a shot of Doc Jones with 47 of his closest friends.

But a bass, besides looking silly in a sweater, doesn't have the same options. It has to change its behavior and its internal physiology to deal with the extremes of cold (and heat).

Temperature and Activity

Berkley fish guru Dr. Keith 'Doc' Jones observes in his book "Knowing Bass" something many bass fishermen take for granted: Successful bass fishing requires finding active fish.

And finding fish "requires you to know how bass respond behaviorally to physical variations within their habitat," he notes. Finding active fish "necessitates a knowledge of how bass respond internally, or physiologically, to these same variations.

"For the angler, the consequences of these responses are not the same at all. How bass react behaviorally determines where you will find them from moment to moment." And "their physiological response sets their mood once you find them."

A bass' metabolism runs best when it is in its preferred temperature range: It can hunt better, feel better and live better. So it uses its ability to sense temperature as it swims to find more comfortable habitat. Generally bass gravitate toward warmer water, up to around 90 degrees F.

Temperature and Seasonal Behavior

Bass get really active in the fall as they seek to avoid winter's approach – they do not like that cold water. But eventually they have to settle down to endure the cold.

A bass actually 'metamorphosizes' (it changes) to acclimate for winter. It has multiple variations of key enzymes to carry out metabolic functions, and as temperatures shift, so does the composition of its cellular proteins. This keeps the fish from getting completely shut down, as these enzymes are sensitive to temperature.

Below 40 degrees F, a bass is going to become dormant. When it's cold like that, "at any given time, a large portion of the bass population will be resting with their pelvic fins and tails in contact with the bottom, wholly inactive," Jones says.

Bass will be "capable of short bursts of prey (and lure) pursuits." But they tire easily, their ability to move is limited, and it takes them a long time to digest any prey they catch.

Frequently they lose weight over the winter – which is what makes spring so great.

Spring must be a huge relief for a bass. The metabolic adjustments run in reverse to acclimatize the fish for warmer water. Especially important to anglers is that their nervous system readjusts toward warmwater survival as spring progresses.

They do not – and maybe they can't – maintain the same lure preferences throughout the spring warming period. Transitional bass probably don't have a constant perception of their world. "What and how they see, hear, feel, taste, and smell may all pass through various phases according to acclimatization state," notes Jones.

The cartoon by Bill McElroy titled target="_blank">"Pre-Spawn Mood Swings" is particularly accurate.

Take-Away Points

> Trend toward smaller and slower baits in cold water.

> Speed up presentations and increase lure sizes as the water warms and the bass become more active and aggressive.

> Often bass will scatter and roam in fall looking for the last warm water around, and they're feeding up for winter. Cover water and fish sun-warmed areas, especially late in the day. On the other hand, at times they will stack up like cordwood in feeding packs.

> Largemouths and spotted bass in an experimental situation settled on a preferred temperature range of 86 to 89 degrees F, much warmer than most North American fish species. Smallmouths preferred just slightly cooler temperatures than the spots.

> Big bass get the choice spots, with the best available combination of temperature, pH, oxygen, predator protection and food.

Notable

> Table 6-5: Spring Behavioral Progression of Largemouth Bass in Jones' book is an awesome chart of bass behaviors vs. temperature.

> When a bass quickly moves from one temperature of water to a warmer or cooler mass, its body temperature gradually changes to match the surrounding water. Bass warm up about 30 percent faster than they cool down.

> Dr. Keith "Doc" Jones is director of research at the Berkley Fish Research Center in Spirit Lake, Iowa. His book "Knowing Bass, The Scientific Approach to Catching More Fish" is available at amazon.com, Barnes and Noble, and other booksellers.