Combined Results of 34 Published Tracking Studies

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.