Stream Smallmouth Bass Migratory Behavior
By Dave Votaw

Here in the Midwest we regard smallmouth bass (Micropterus dolomieu) as ‘our’ fish. After all, smallies are native to the rivers of the Midwest, having occupied them about 14,000 years ago following the last ice age, and eventually finding their way to the Great Lakes, including Lake Erie, the smallmouth bass capital of the world. One would think we Midwesterners had patterned the behavior of these river fish we love so much by now, but much remains to be learned about migratory behavior, especially through the cold weather months. Current research is shedding new light on winter habitat and migratory behavior of smallmouth, finding variable behavior between populations of these fish: some populations are primarily sedentary, while others migrate long distances to winter habitat, returning to reach spawning grounds in the Spring.

Studies of smallmouth movements rely on either radio telemetry or recovery of marked individuals. Studies of post spawn summer movement have found that adult smallies remain within a relatively small area; for example, in two southern Michigan streams, smallmouth moved less than 1 km over the summer. Smallmouth bass fry can be displaced downstream under flood conditions, probably suffering high mortality; survivors likely populate downstream areas since fry move little. However, several studies of recovered juvenile smallmouth suggest that a percentage are mobile in summer moving as much as 40 km. Lyons and Kanehl’s seminal 2002 review concluded:

Nearly all stream dwelling smallmouth bass populations are largely sedentary during the summer, and some populations appear to be sedentary throughout the year. However, other populations undertake migrations, mainly in fall and spring, and there may be substantial variation among individuals within a population in the extent of movement.

Although movement during the transition period from warm to cold water conditions is of great interest to fishermen, few studies during this season have been conducted. Some studies suggest that northern reaches of the smallmouth bass range exhibit long distance migrations possibly due to the severe winters experienced in the north. Long distance migrations of 35 to 109 km have been documented in northern Wisconsin, beginning when water temperatures fell below 60F and particularly when accompanied by rainfall and increased flows. Young of the year and age 1 fish did not migrate. Many fish were observed to return in spring to the same general area they had occupied the previous summer.

Recent studies have also given us new insight into winter movement of stream smallmouth bass. Most of us know the conventional wisdom that smallmouth move to the deepest slow water within their migratory range and settle under some kind of cover for the winter. In some populations, smallmouth were found to occupy the deepest water available during winter. However, other studies have found that winter activity levels vary among populations. For example, Huron River smallmouth have often been observed in open water away from deeper water or cover and moving as much as 100 m regularly in water near 32F. Lyons and Kanehl confirmed the winter movement patterns and habitat use using radio telemetry, finding regular short-range movements of several hundred meters in water less than 2 m deep over rocky substrates. However, these fish also did not associate with the usual in-stream summer cover.

Finally, to complete the cycle, both river and lake smallies move into tributaries in spring to spawn. These tribs then provide nursery habitats for fry. In some instances these spawn migrations are not long, and spawning may even take place in the same general area where adults spend the rest of the year.

Interestingly, stocked or transplanted fish tend to leave the stocking areas quickly and move large distances downstream. Pond-raised fish and native captured smallmouth were stocked in Ohio’s Little Miami River [Brown 1961]. The native fish remained within approximately 0.8 km of the release point, compared with the hatchery fish that moved as much as 113 km downstream. Thus, if stocking is to improve populations in streams, wild caught fish from the same drainage should be used. Research has demonstrated that some smallmouth bass populations make specific fall and spring migrations. Biologists hypothesize that this behavior is controlled genetically, making it important to preserve this adaptive behavior by not mixing populations.

Stepien, Murphy, and Strange [2006] investigated the fine-scale population genetic structure of smallmouth bass because it is so important to preserving genetic integrity and diversity. They note that because smallmouth demonstrate a homing tendency for spawning, smallmouth have the potential for significant population genetic structure and fine-scale genetic differentiation. In short, these authors found that despite the opportunity to mix genetically, close geographical sites often showed marked genetic differences, especially among river smallmouth bass populations because adults return to their own natal sites to spawn. In practical terms for fishermen, this means the smallies in adjacent but separate watersheds are possibly genetically distinct, and thus may exhibit distinct migratory behavior through the seasons.

References:

John Lyons and Paul Kanehl. Seasonal Movements of Smallmouth Bass in Streams. American Fisheries Society Symposium 31:149-160, 2002.

Carol A. Stepien, Douglas J. Murphy, and Rex Meade Strange. Broad to Fine-Scale Population Genetic Patterning in the Smallmouth Bass Across the Laurentian Great Lakes and Beyond: An Interplay of Behaviour and Geography. Molecular Ecology 2006.

E. H. Brown. Movement of Native and Hatchery-reared Gamefish in a Warmwater Stream. Transactions of the American Fisheries Society 90:449-456, 1961.