Coalesce is a wonderful word. It describes a process wherein disparate parts, people, meanings—even fish—come together to form one whole, or concentrate in one area. To “become one” with something is to coalesce with it.

That’s why what John Lyons and Paul Kanehl of the Wisconsin Department of Natural Resources have done for fishermen is a wonderful thing. They performed a radio-telemetry study, tracking smallmouth bass in two Wisconsin Rivers. And, in the process, they compared information from 34 published studies on the movements of smallmouth bass in rivers, eight of which involved radio telemetry. The result, Seasonal Movements of Smallmouth Bass in Streams (AFSS, 2002, by John Lyons and Paul Kanehl, Wisconsin DNR), is a must read for river smallmouth fishermen.

“Lotic (river-dwelling) populations of smallmouth bass have been the subject of scientific studies for more than 100 years,” Lyons and Kanehl wrote. Those radio tracking and tagging studies provide a wealth of information revealing not only how dynamic stream smallmouths can be compared to their lake-bound cousins, but also how vulnerable and fragile these populations are. “Despite a long history of research, however, much remains to be learned about smallmouth bass movement patterns and habitat use, particularly from fall through spring.”

Fall Movements

Lyons and Kanehl performed their radio-telemetry study on Otter Creek and the Pecatonica River in southwest Wisconsin from 1992 to 1993. But research includes findings on the seasonal movements of smallmouth bass in rivers of 14 states and Ontario, and the paper reviews and summarizes smallmouth studies by biologists around the continent. From Alabama, Tennessee, and Massachusetts to Oregon, Ontario, and Michigan, these studies blanket the range of smallmouth bass and cover a variety of climates and types of riverine habitats.

They found that latitude and climate have a lot to do with smallmouth behavior in rivers over the course of the seasons. “In fall,” they wrote, “some smallmouth bass populations remain sedentary, while others migrate more than 45 miles to reach winter habitat. Migration distance is correlated with winter severity; smallmouth bass move little in streams that do not freeze, but often move more than 3 miles in systems with ice.

“Winter habitat and activity levels vary among populations and have little obvious relation to winter severity, however. In some systems, smallmouth bass occupy the deepest available water or areas of cover (boulders, logs) where they remain inactive for the winter. In other systems however, smallmouth bass avoid the deepest holes and are often active in areas with little cover all winter.”

For anglers, this rings true. Smallmouths near the northernmost part of their range, in Lake Superior, are easily caught through the ice most days in winter. Yet, 100 miles south, on the Mississippi River, smallmouths become almost impossible to catch after the water drops below 40°F in late fall—let alone during midwinter, through the ice. Near the warming influence of hot-water discharge sites in the same region, on the same river, however, numbers of smallmouths can be caught in open water all winter.

Tagging studies on the Mississippi by the Minnesota DNR reveal that smallmouths tend to migrate to deep wintering holes—usually to plunge pools below dams, reservoirs above dams, or to confluence holes at least 20 feet deep. These migrations were shown to cover 20 miles or more in some cases.

But winter “sanctuaries” differ from river to river, depending not only on latitude, but also where smallmouths find the greatest environmental stability. “In one segment of the Jacks Fork (Missouri), many smallmouths left the main stem when waters cooled below 59°F in fall and entered a tributary spring with constant winter temperatures of about 56°F,” according to Lyons and Kanehl. “They remained there until main-stem temperatures increased above 59°F the following year. The distances smallmouths traveled to reach the spring run were unknown.”

Some studies reveal that smallmouths don’t migrate far at all during autumn, and some bass stay in relatively shallow water. As we travel north, and as winter environments grow harsher, the more crucial quests for deep havens become. But nothing is constant, and no easy formulas exist. In Lyon’s study on the rivers of southwest Wisconsin, in 1992, smallmouth bass with transmitters moved in three stages from summer to winter habitats.

The first stage took place from late August to early September, when flows were steady and water temperatures were 59°F to 62°F. The second period began one month after tagging, in mid-September, when water temperatures were 56°F to 59°F. The final period began in mid to late October when cold weather forced water temperatures to dip between 48°F down to 38°F.

In 1993, the same bass in the same system began migrating as water temperatures again reached the 59°F to 61°F zone. Yet, radio telemetry studies by Dr. Mark Ridgway of the Ministry of Natural Resources in Ontario revealed that smallmouths in lakes he studied moved every year on approximately the same calendar date—within a few days of the vernal equinox—regardless of temperature. Do river bass follow different cues? What’s the primary cue that triggers smallmouth migrations—day length or water temperature? Apparently, the answer may vary a bit from system to system, perhaps even from year to year.

“Radio telemetry showed that wintering habitat in the Pecatonica River is characterized by slow-moving runs 3 to 6 feet deep. Even though deeper pools of 7 to 10 feet were available nearby, smallmouths preferred to hold in these mid-depth sand and silt runs. Though sand and silt were the primary substrates in these runs, smallmouths were almost always found hovering near patches of gravel and rock. Though wood cover abounded on the nearby banks, and while bridges and boulders were nearby, smallmouths were seldom observed using those cover options in winter.

“It had been generally accepted that in winter, smallmouth populations moved to the deepest, slowest water available within their home pool and became quiescent next to or under a boulder, ledge rock, or log. In some populations, such as the Snake River (Idaho), Wapsipinicon River (Iowa), and perhaps the Maquoketa River (Iowa), smallmouth bass occupy the deepest water available in winter. Several studies indicate, however, that winter habitat and activity vary among populations, “ Lyons continue. “Smallmouths did not consistently use the deepest water present in the Jack’s Fork (Missouri), Wolf River (Wisconsin), Huron River (Michigan), or Fox River (Illinois). Jacks Fork fish were strongly associated with large boulders in winter, but Huron River fish were commonly found away from cover in open water or along stream banks.”

From observations with other stream fish in winter, we suspect Pecatonica River and Huron River smallmouths may prefer mid-depth runs and open water in winter because sunlight penetration is greater there than in deep pools—which might also explain why they avoid woodcover, bridges, and boulders. Perhaps they want to feel the sun on their backs as much as possible when water temperatures hover near the freezing point. As the study points out, wintering smallmouths don’t always hold in deep pools, even up north. But other studies reveal that many populations of smallmouths use deep pools and cover during winter, suggesting that smallmouth behavior is not static from stream to stream, and that at least some unique adaptations occur in each environment smallmouths inhabit.

Conventional wisdom paints a picture of torpid, near-hibernating smallmouths in stream environments during winter, especially up north. “In our radio-telemetry work, we did not observe any long-distance movements once smallmouths had completed their fall migration to their overwintering habitat,” Lyons and Kanehl observed. “However, all of the six fish we were able to track throughout winter displayed extensive and regular short-term movements, despite water temperatures that were consistently less than 33.8°F.” Even in water that would probably be frozen if not moving, smallmouths may become active on a daily basis.

Spring Movements

“Many river-dwelling smallmouth bass populations moved into tributaries to spawn in spring when water temperatures exceeded 50°F,” Lyons and Kanehl declared, referring to a variety of studies. “These tributaries comprise important summer nursery habitat for young-of-the-year fish. In the Des Moines River (Iowa), some adult smallmouth bass moved more than 3 miles into tributaries to spawn, whereas other adults spawned in the river. In the Columbia River of south-central Washington, tagged adult smallmouth bass moved out of the main river in May to spawn in tributary sloughs and backwaters, remaining there until July or August. Some recaptured individuals had moved up to 38 miles to find suitable habitat.”

Study after study reveals that smallmouths in rivers tend to be far more mobile than smallmouths in lakes, and often cover many miles to find suitable seasonal habitat. The habitats smallmouths choose each season seem to have been determined thousands of years ago, as bass return to the same areas to spawn, summer, and winter every year in most environments.

“In northeastern Wisconsin, adult smallmouth bass left the Wolf River to spawn in the smaller Embarrass River when water temperatures reached 59°F in May,” the study continued. “They moved as much as 45 miles upstream in the Embarrass River and remained there for the entire summer.”

Other studies have revealed that much like their lake-dwelling cousins, some stream smallmouths migrate short distances between winter, spring, and summer habitats—if at all. “In some rivers, smallmouth bass did not make long-distance migrations to spawning areas and instead spawned in the same general area where they spent the rest of the year. Limited or no spawning movements were found in the Snake, Jacks Fork, and Huron.

“In our study, we observed an apparent spring spawning migration. We tracked six smallmouths during this period, five that began the spring in the Pecatonica and one in Otter Creek. Two major movement periods occurred, both associated with floods. The first period was in early May, when river flows were receding from levels three times higher than normal and minimum water temperatures were 50°F to 54°F. Two of the smallmouths moved from the Pecatonica back into Otter Creek. One fish resided for the remainder of spring and summer near where it had been initially released after radio implantation. The second movement period came during early to mid-June, when flows increased by a factor of two, and minimum water temperatures increased from 54°F to 61°F.” Among the five fish that did migrate to spawning habitat, then on to summer habitat, the average distance covered was about 4 miles and the longest distance covered was over 7 miles. Some fish moved upstream to spend the summer, some moved down.

Smallmouths everywhere tend to spawn within a window of water temperatures ranging from slightly below 60°F to about 64°F . Every year, in every riverine habitat studied with tag returns or radio telemetry, smallmouths seem to start moving out of wintering habitat when water temperatures approach 50°F , and they soon appear near spawning habitat. By the time the water reaches 60°F, every smallmouth that is going to spawn is on or near spawning habitat. But some studies have also shown that not every mature smallmouth spawns every year, which perhaps explains why one smallmouth in the study by Lyons and Kanehl didn’t migrate at all in spring or summer.

How far do smallmouths migrate in spring in the rivers and creeks you fish? It isn’t possible to answer that question based on latitude, climate, or by what the bass do in other rivers nearby. Each stream environment seems to invest within its smallmouth populations a genetic propensity to follow the unique drumbeat of that system’s characteristics. Apparently, smallmouths will seek near-perfect habitat for each season, regardless of the distances involved.

Summer Habitat

Once smallmouths migrate to summer habitat, conventional wisdom indicates they stay put unless floods or severe drought force them to move. This has been the assumption of most avid bass anglers, and most biologists, for many years, the theory buoyed by several early studies.

“Nearly all published studies on summer (defined here as postspawn, from mid-June through mid-August) movements have been based on recaptures of marked fish and have concluded that smallmouth bass stay within a relatively small area of a stream or river, often a single pool, unless environmental conditions become extreme,” Lyons and Kanehl wrote. “For example, in Jordan Creek (central Illinois), Larimore (1952) found that most tagged smallmouth bass had home pools that they rarely left during the summer, and that they occupied the same pools in successive years. During severe drought, smallmouth bass moved over a mile downstream as their habitat dried up, but returned when the drought ended.”

Studies in Indiana (Gerking, 1953, 1959) discovered much the same thing. Smallmouths in those streams remained within reaches less than 365 yards long, and tagged fish were found in the same pools for several years in a row during summer. On the Snake River along the Idaho-Washington border, Munther (1970) reported that “most recaptured individuals came from the same pool where they were tagged, and 95 percent were recaptured within .75 miles of their release point.”

Smallmouths of the Jacks Fork in Missouri, however, ranged up to about 3 miles. Studies on the Des Moines in Iowa revealed that some smallmouths moved as much as 2 miles in summer, while most bass with tags moved no more than a quarter mile. In the Deerfield River in western Massachusetts, radio-tagged bass had home ranges that varied from 70 yards to over a mile.

“In our radio telemetry study,” continued Lyons and Kanehl, “five adult smallmouth bass were tracked during the summer of 1993; four in Otter Creek and one in the Pecatonica River. All of these fish stayed within a small area, never moving more than 200 yards upstream or downstream. In late June, an extended flood created flows more than two times normal, but no substantial movement occurred during this event. By mid-August, however, smallmouth bass began to leave Otter Creek on their migration to winter habitats.”

Since smallmouths tend to use the same seasonal habitats year after year, it must be assumed that their chosen summer habitat has the potential to provide a stable source of protein every year, with lots of rearing habitat for minnows, crayfish, aquatic insects, and a steady supply of plankton, since the metabolic requirements of smallmouths are greatest in summer. These areas tend to have structural diversity with inflows from lakes, tributary streams, or springs. The classic “riffle-pool” habitat of summer smallmouths provides oxygen through the mixing action of water running over shallow rock. The rocks and subsequent eddies provide plenty of habitat for crayfish and minnows, and the deeper pools gouged out downstream of the riffles provide prime areas for smallmouths to rest or hide.

The Susceptibility Of River Bass

Anglers have a dramatic impact on smallmouth bass populations in streams. Studies on the Maquoketa River in Iowa from 1994 to 1995 indicated that every smallmouth over 6 inches long was caught an average of 6.3 times during that period. “Some of the bass were caught 9 or 10 times,” biologists told us. If not for special no-kill regulations, smallmouths over 10 inches could have ceased to exist in the Maquoketa for years, which would devastate year classes and send the population into a downward spiral, which is difficult to recover from.

Stream smallmouths can be aggressive, and biologists have often noted that anglers can easily develop misconceptions about the size of the population. Life can be harsh in streams and rivers. Floods, droughts, and exceptionally cold winters can literally kill fish and dramatically affect populations of prey species and the strength of year classes for smallmouth bass.

Some observations and conclusions by Lyons and Kanehl: “Smallmouth bass fry are susceptible to displacement from high flows and may be carried many miles downstream by floods (Larimore and Duever, 1968; Simonson and Swenson 1990). Evidence suggests that survival of fry displaced long distances by floods is low; downstream drift of smallmouth fry during nonflood years appears to be uncommon at best.”

Regarding establishment of special-regulation areas:

“If special fishing regulation areas for smallmouth bass are to be established in streams, then these areas should include the potentially large annual home range of smallmouth bass. Although it may seem impractical to cover an entire home range with special regulations, the regulation area should be as large as possible. Ideally, the regulation area should include locations where smallmouth bass are most vulnerable to anglers during fall and spring migrations.” They went on to cite the Zumbro River in Minnesota, where 40 percent of the smallmouths tagged within a special-regulation area were later caught by anglers outside the area.

Regarding stocking practices:

“Stocking does not appear to be useful for enhancing smallmouth bass populations in streams. Transplanted smallmouth bass tend to leave the stocking area rapidly and often leave the stream itself, typically moving downstream. If stocking were to be done, it would be best to use wild-caught fish from the same drainage system. At least some smallmouth bass populations undertake long and specific migrations, and the tendency to make these migrations may be controlled genetically. If there is a genetic component to smallmouuth bass movements, then it will be important not to mix populations and risk losing adaptive migratory behaviors through introgression.”

Regarding dams, culverts and crossings:

“Long-distance movements are an important component of the life history of smallmouth bass populations in some systems. Therefore, dams and other structures that prevent or impede movement will (negatively) affect these populations. On smaller tributaries, road crossings, and culverts should be designed to allow passage by adult smallmouth bass so that spawning areas are not cut off. Effective upstream and downstream passage for adult smallmouth bass should also be pursued at dam sites.”

As we increasingly impact and alter the course of our rivers, let’s hope that common sense prevails and consideration is given to the needs of smallmouths and other wildlife that depend on flowing water, so that all studies we’ve funded come to some meaningful end—so that our grandchildren will still be able to catch smallmouth bass in the rivers they inherit from us.