As a forester, I spent countless hours over 30 years walking out creek and river bottoms often evaluating wetlands, gaining a good concept of those terrestrial systems. Understanding them helps me visualize what lies under lakes. I developed a habit of imagining those places at the bottom of lakes, something any hiker can do by simply walking around in an area that could be impounded by building a dam. Knowledge of potentially flooded forest, prairie, pasture, cornfield helps understand flooded lake structure and cover. Certain species of trees and brush grew in shallow water in creeks and along rivers. Huge trees lining waterways had been passed over through several timber harvests, too large for any sawmill, too difficult to harvest anyway. Those would be left arching over a flooded river or creek channel.
Your visit will reveal many interesting features that could end up flooded with boats overhead looking down with fish finder sonar. Along a creek, you might come across a short rocky bluff overhanging the creek bed. Flooded, if shelves of rock stick out with recesses caused by erosion of softer soil material, we call it a ledge. If the surface is flat or slightly rounded, vertical or sloped, it’s a bluff. It might be stepped back with rock shelves appearing to be dug into the hillside, a series of ledges. There are mounds scattered along the way, clay soil supporting a tree or two resisting erosion of sandy soil between mounds. Someday a boater’s sonar might see that or an ancient Indian burial mound as a round-topped “hump” maybe still showing a flooded snag with branches or just a stump covered with aquatic growth. A junction of two creeks making one large creek might have a deep hole gouged out by raging high water pouring off a mountain. A sonar might pick that up as a sudden drop-off next to a deep channel, jam-packed with fish on a hot summer day. A ten foot high former creek waterfall becomes a flooded small bluff sure to attract bass. The creek splits into two twin creeks along each side of a resistant raised rock “ridge” where bass can suspend on the ridge between rocks watching baitfish traffic through the old creek channels. The creek winds through a large “flat” that might have been used to grow field corn decades ago, the farmer’s plow rows still rippling across the bottom. Those furrows can often be seen on a sonar screen as ordered straight parallel ripples. An occasional man made canal crosses the fields to solve an old drainage problem, draining the field after the river flooded. The creek passes through a narrow pass between two small hills that almost touch. Later that might be seen as two islands with long points; the ridge “saddleback” flooded. Once flooded, all those features and many more, such as old home foundations and their root cellars now caved in, become frozen in time; changing little or none other than to be covered ever deeper by sediments washing down from up stream.
We consider permanent parts of the bottom to be “structure”. The creek channel is a structure. So are the ledges, the humps, hills, points, holes, gravel and sand bars, plow rows, rock rubble at the foot of a hill, an outcrop of solid rock, an old concrete bridge, culvert, road bed, railroad bed, concrete blocks that held up a house. All the permanent fixtures that are “forever” make up a lake’s structure, those features every generation of fish learns is always there to shelter them. There is some confusion using the term, biologists referring to the whole interaction of life and mineral as a lake’s structure, not using the fisherman’s “cover” term. Some anglers mix and match features interchangeably; calling cover a structure.
Cover is generally the temporary shelter material that comes and goes, sometimes attached to a lake bottom, lying on it, suspended or floating on a lake surface, growing on land over water. Tree stumps (cover) last a long time under water, but they eventually rot away or are undermined by current and swept away. Brush that grew along a creek dies off, and dislodges, collects in piles out of the way of current and adds non-living cover until it too is gone. Brush that established after flooding provides a living cover along a shoreline or standing in water. Aquatic vegetation develops to replace the terrestrial growth that was so dominant before flooded. But that too is subject to seasonal change, flourishing in warm water, dying back in winter. “Laydowns”, trees above the shoreline that fall into the water; provide cover a few years, until another storm or beaver activity replaces them. Anglers add cover each winter by sinking Christmas trees, wood pallet creations, and other fish attractors, all “cover”, and sometimes the only cover fish will find in a lake. It’s important to separate what is temporal, only present seasonally, there one year, gone the next, from what can be counted on as always present. Fish become experts at knowing the differences, and so should the serious angler.
Immature bass are about as inclined to inhabit structure and cover as they are to live in open water. They expend a lot of calories negotiating open water existence following schools of shad or other baitfish, swimming long distances as mobile predators. Their habits are less predictable, so it makes sense to investigate mature bass preferences for structure and cover through their life cycle seasons. The more mature a bass becomes, the more energy conservative they become, increasingly relating to structure and or cover. It’s rare that an eight pound largemouth bass will be found suspended over a large gravel bed. They get old by hiding and remaining as far out of reach of predators, such as anglers, as possible. The closer they can stay to something that can break up their image the better. They will hug a stump for hours or suspend under a ledge, letting food come to them. That limits their exposure to detection.
The big question of most anglers is when to look to structure or to cover to find bass. Natural cover is mostly found in shallow water under about 25 feet while the structure is present from the shoreline to the deepest parts. Understanding when and why bass relate to deep or shallow water is a key in deciding which to search out. There are many reasons a bass might prefer to stay deep and therefore limited to available structure. A situation would be that’s where baitfish are, following phytoplankton and zooplankton, the microscopic life forms they feed on following organic particles driven by water (deep) or wind (shallow) current. Assuming there is sufficient dissolved oxygen content, they can live at great depths, limited only by sufficient sunlight penetration, deeper in clear water. They will choose a certain depth supporting the most comfortable temperature range. When any lower food chain change occurs, the upper food chain (predators) must adjust or go hungry. Another reason is for instance in post spawn. Bass will have spent weeks and sometimes months extremely exposed to discomfort in very shallow water and rarely if ever inclined to feed even in the presence of bountiful food supplies. They lose weight, burn fat, and when spawning is complete, retreat to the deepest comfort level possible to “get away from it all” and recuperate. That never falls below a thermocline beginning to develop as surface water warms. Below a thermocline, there isn’t enough oxygen for survival beyond minutes. Observing that mixing layer between deepest, coldest deep water (hypolimnion) and the warmer, oxygenated shallower, warmer water (epilimnion) is very important, eliminating a huge portion of any lake, no matter how interesting a structure you can find below that layer. It’s simply the zone of rapid temperature change from cold to warm where oxygen is mixed with “dead” water below. Oxygen only absorbs so far, however much current is able to mix the two water layers present in most lakes. Within a few weeks, the weak bass manages to catch enough prey to regain strength, leaving the sanctuary of deep structure for shallow structure and ultimately cover.
Bass will relate to cover as soon as possible because most of their preferred prey soon relates to cover when shallow water warms enough to keep the lower food chain around cover. When the bass arrive in shallow water, they find good hunting and shelter around familiar structure, and will visit the less protective cover to feed, then retreat to deeper structure nearby. Eventually aquatic cover grows dense enough to match the protective features of deeper structure, many mature bass choosing to spend feeding and resting hours alike under mats of hydrilla or lily pads, remaining invisible to predators above. When some species of invasive plants grow so thick a bass can’t safely penetrate it, they become more “edge” oriented, and if they can’t get under the cover must retreat increasingly to deeper structure to rest, returning to shallow cover only to actively feed.
Approaching fall, a bass finds living cover depleting, the baitfish that feasted there relating more to open water, drawing predators out with them, especially near mouths of creeks. They also swim into the backs of coves, wherever they can find the lower food chain driven by wind or water current. Mature bass continue to favor deeper structure and available cover from deeper water to back of coves, familiar with roaming schools of prey migrating back and forth. They don’t swim far chasing schools, but wait patiently along a creek bluff in an outside bend; where current is more likely to drive schools along. When immature bass follow schools of baitfish out into deeper water, mature bass tend to hold to structure ambush points, from there occasionally swimming a few hundred feet below school activity picking off injured and disoriented baitfish fleeing from a feeding frenzy. An angler following and fishing open schools of baitfish and feeding bass will usually catch immature bass. Learning the routes of baitfish coming and going is a better plan. It’s productive to record waypoints on a GPS wherever baitfish are found, eventually leading to consistent patterns of travel. An angler targeting interesting structure along a route, jigging around ledges, humps, bluffs, boulders, and other structure, is more likely to present bait to a mature bass that wouldn’t expose itself or expend energy chasing a school above it. The big bass prefers to lie in wait for an easy meal to swim by, so baits ought to accommodate that preference. Mature bass tend not to move far from a general spot they use as “home”. One lone bass will choose one area of a lake that affords shallow cover, like a flat covered with vegetation, within a few hundred yards of a deep-water structure hiding place. They are willing to follow the forage between those extents of their home domain. The exception is during the spawn, though the oldest bass will often take up permanent residency in an ideal area near preferred spawning grounds. There is a very strong “pecking order” among bass, the immature fish taking whatever habitat is left to them. This is why many anglers focus on “sight fishing” during the spawn, for the purpose of identifying those ideal habitats that will always have mature bass living year around. That’s one of those deep secrets of some bass anglers, not out there just for the pleasure of catching some large bass. If you find a spawning area near deep water with plenty of structure and shallow cover close by, you are close to a “hot spot”.
Once winter settles in bass must find warmer deeper water, being cold-blooded, unable to do anything else to warm up. They are driven from cover; relating more to deep structure. Mature bass will not normally relate to open water away from protections of submerged trees, rock formations, or other favored structures. Immature bass will often suspend shallower above mature bass, taking up a less protected layer of water, under baitfish. Baitfish, more susceptible to low temperatures than larger bass, are also forced deeper, often suspending around deep cover or structure, sometimes right over the winter home of large bass. When the weather permits some warming of shallow water, baitfish will move in for a brief feeding, followed by bass. If there is some shallow cover, the entire food chain can be found briefly there, affording easier access to bass. As the sun sets all the fish return to the deep. It’s quite well known some bass remain shallow more than living deep, so some can be located in shallow water all year long, retreating only when pressured by anglers, boat traffic, or suffering discomfort from a passing cold front or freezing water. Those bass often claim large stumps near shore, stump holes, lone boulders, and other resting places from which they stage feeding forays. When cold they are not very alert, anglers seeing them against a stump or rock only a few feet away, reluctantly swimming off when agitated enough.
During pre-spawn bass begin making trips up creek channels out of their deep structure home, finding baitfish becoming more active and easier to locate, as the prey seek the lower food chain as soon as they can take the colder shallow water. If nights suddenly cool down the migration is back and forth as in the fall, so bass are scattered as in fall, somewhere between their maximum habitat extents. The best fishing opportunity is over creek channel structure during pre-spawn. When the water warms enough to begin building beds the male bass stays behind in shallow areas while the females feed until hormones stops their hunger. They relate to the creek channel structure until male bass come out to escort them into the shallow beds.
That brings us around full circle for a general concept of when and why bass relate to their “furniture” scattered about their homes. This is by no means even close to the larger body of knowledge held by anglers and fisheries biologists, so it is my hope an extended discussion about the bass’ use of structure and cover will follow in the member forum here at Ultimatebass.