While field testing once in Florida, my guide and I came across the curious sight of a bass floundering helplessly at the surface. We discovered that the 4-pound bass had a prey fish lodged in its throat. The meal was too large to go forward, yet too stuck to back out. The prey in this case happened to be another bass; a 3-pounder. Neither bass survived, and I have often suspected the victim died deeply resenting its captor's poor lack of judgment.
Exceptions such as this notwithstanding, most feeding bass practice size selection. In fact, size is one of the primary criteria by which bass choose their prey. Bass look to optimize their meal size, attacking prey that is neither too large nor too small, but falls within a preferred size range.
Bass practice prey size selection as soon as they start feeding, demonstrating that size selection is instinctual. Selection might be controlled by the optics of the visual system. Young bass may shy away from oversized meals by avoiding large images cast on the retina. Ultrasmall prey may be overlooked simply because they lie below the animal's visual detection threshold.
Choosing the right food size becomes increasingly a learned behavior as a bass grows and gains experience. The bass learns to more accurately predict the prey sizes it can and cannot handle. Since prey size is often directly related to its ability to escape, struggle, and inflict injury, young bass quickly learn the harsh consequences of biting off more than they can chew!
Research at the Berkley lab shows that bass not only apply size selection principles to artificials, they have their size optimums. For active bass in the 1- to 2-pound range, lures of 2.5 to 3.0 inches evoke the strongest responses. Smaller lures received fewer strikes, as did larger lures.
Although small finesse-style baits regularly catch big bass, and small bass are sometimes taken on big baits, bass anglers still relate lure size to bass size. Small lures catch small bass; big lures catch big bass.
The real dilemma for anglers on the water comes in choosing the best lure size for any given population of bass. Missing the optimal size doesn't spell instant failure, but it does mean a lower catch rate. Lures that are too small fail to stimulate bass, whereas oversized lures tend to inhibit strikes. The reasons behind the discriminations are different, but the results are the same?fewer bass in the boat.
Determining the best lure size to fish with will always be a dynamic process. Natural bass populations are always mixed in size, and their feeding moods constantly swing back and forth from aggressive to passive. In general, however, bass are more tolerant of lure downsizing than upsizing. Decreasing lure size usually has a minor effect on catch rates. In contrast, even minor increases above the size optimum can yield major decreases in catch rates. If your catch rate falls off after upsizing, you are beyond the preferred size. Downsizing the lure is in order. But, if after downsizing your catch rate falls off, odds are the lure is smaller than the optimum size and you need to go back up a step or two. An increase in catch rate indicates a movement in the right direction.