Why are bass where they are?

Mickey Aldridge and I were off on a bucket-list fishing trip. Destination: Lake St. Clair, Mich. The mission: pre-spawn smallmouth bass.

Aldridge is a serious fisherman and good bass stick who fishes local and FLW tournaments. Shortly after we had my truck and boat pointed north, he asked, “All right Mr. fisheries biologist, why are bass where they are?”

With 14 hours of windshield time ahead of us, the question was worth pursuing. Quickly realizing that I stood to give a lot of information and get little in return, I turned the question back on the experienced angler: “Why do you think bass are where you catch them, spawning season excluded?”

“Comfort and food,” he responded.

I think Aldridge’s answer is absolutely correct. Food is easy to understand — for bass, it’s anything that is alive that the bass can catch and suck into its mouth.

But what is comfort?

“Comfort” can include a lot of things — biologists call them variables — but in Mississippi waters I think temperature and oxygen content top the list.

Preferred or optimum temperature for largemouth, smallmouth and spotted bass is about 80-84 degrees. That is the temperature range they select in laboratory trials, and that is the temperature range where their physiological machinery is most efficient. Bass can survive (and be caught at) temperatures down to near freezing and above 90 degrees, but they will occupy their preferred 80 to 84 degrees when they can find it and if the water has sufficient oxygen, the second and an essential comfort factor.

Back to the question: Why are bass where they are? In the cool seasons, look for bass in the warmest water you can find. In the Mississippi summer, when surface water temperatures start hitting 90 degrees, look for cooler water.

The cooler water may be in coves with cooler water flowing in, it may be in shallow pockets with a lot of vegetation that reduces solar warming of the shallow water column, or it may be the thermocline in larger, deeper-water reservoirs that thermally stratify.

In the shallow, weedy water and deep-water reservoirs, temperature and oxygen interact to affect the distribution of the bass. If the cooler water doesn’t have sufficient oxygen, the bass won’t be there.

Biologists consider five parts per million “sufficient oxygen,” but that means little to anglers because even the best-equipped anglers don’t carry expensive oxygen meters. The best way an angler can tell whether the water has sufficient oxygen is to look for fish — if you see fish swimming, the water probably has enough oxygen.

Shallow water with dense weeds can lack oxygen, particularly early in the morning, because at night the plants are using oxygen. If you don’t see small fish swimming around and you aren’t getting bass bites, there is a good chance that area lacks sufficient oxygen throughout a 24-hour period to support bass.

In deeper reservoirs that stratify in the summer, cooler water is available below the thermocline — the zone of the water column where temperature rapidly changes. Mississippi reservoirs are generally fertile and lack oxygen in the deep waters.

The way to tell if the deeper waters lack oxygen is, again, look for fish, but now you will be doing the looking with your sonar. The fish will tell you where the temperature and oxygen conditions are best. Fish in the deepest water where you mark abundant fish.

After temperature and oxygen, cover is important. Largemouth bass often capture food by searching for and then chasing it, but they are most efficient as ambush predators. The dark shadow cast by a laydown log, the branches in a brushpile, the stems of plants in a weed bed or rocks all help conceal the bass. Cover, therefore, makes the bass a more effective predator. In some cases, the same cover that conceals the bass also attracts the forage.

“OK, all that makes sense,” Aldridge agreed. “But how do you account for the strong bass bite on deep points and ledges?”

Answering that question takes a little guesswork, but I would offer that depth, and the low light conditions that occur there, also are cover. Bass, as other fish, change color to better blend with their environment.

Have you noticed how bass caught from laydowns, rocks or weed beds in clear water are often darker and more vividly marked than those caught in deep or muddy water? A pale bass would be well camouflaged in the dim, shadowy light of a deep-water point or ledge.

Finding the best blend of temperature, oxygen and cover often will go a long way to locating bass throughout the year except during the spawn, but I leave you with one more biological thought: Food can trump comfort. If the food doesn’t come to the bass, the bass go to the food.

I’ve caught largemouth from 100-degree water in power-plant cooling-water discharge channels. The bass were feeding on shad concentrated in the current.

Mississippi bass anglers all look forward to summertime schooling action when the bass drive shad to the warm surface waters that far exceed the bass’s preferred temperature. Yes, bass will leave their comfort zone when they need to, and food satisfies an essential need.