Smallies on the Move

Smallmouth bass really like to travel—at least some of them do. A new study of Mississippi River smallmouth found that some fish make seasonal movements up to 32 miles. By implanting tiny radio transmitters in 30 adult smallmouth bass, DNR Fisheries biologist Eric Altena was able to track their movements for a year.

The study took place in 2001 and 2002 between St. Cloud and Coon Rapids, a 60–mile stretch of the upper Mississippi popular with anglers. A 12 to 20–inch protected slot regulation, with one fish over 20 inches and a three–fish daily bag limit for smallmouth bass govern 47 miles of the river. Monitoring the internally tagged fish year-round, primarily by boat, Altena discovered that movement of Mississippi smallies is quite variable. All the tracked fish made seasonal movements. The most nomadic swam more than 30 miles annually, while others moved only a few miles a year.

One of the biggest homebodies was a fish I had nicknamed "Homer" (as in couch potato Homer Simpson) because my clients (I'm a fishing guide) and I had caught and released the tagged 14–incher three times, always from the same spot. According to Altena, Homer was actually a she, and moved barely a mile a year.

Altena found smallmouth bass travel the longest distances in spring and fall when they move to spawning sites or wintering habitat. Some tagged fish started moving to their wintering areas as early as September, while others relocated two months later. Every one of the fall travelers ultimately relocated to part of the river with slow current. Behaving much like smallmouth bass in other northern rivers, Mississippi smallies remained in these slack-water hibernacula the entire winter.

The study shows fish move the fastest in spring, when hormonally primed smallmouth sometimes swim more than a mile a day to reach their spawning areas, usually gravel-bottomed eddies along riverbanks or behind islands.

Tagged fish occasionally turned up in odd locations. During the high flows of last July, Altena tracked one fish into a flooded pasture and another to a golf course pond temporarily connected to the Mississippi. He speculated that these wanderers were looking for minnows, or perhaps trying to escape strong currents.

The tagged fish were also regularly caught by anglers during the study. Altena got 15 different reports of tagged fish being caught, including Homer and another eager biter that was released four times. None of the 30 fish was known to have been killed by anglers—a testimonial to the hardiness of the species and to anglers' good compliance with the Mississippi's special regulations.

Three died during the winter, but blood found on shoreline ice and other evidence suggests natural predators, perhaps otters, were the cause. At the end of the study, as many tagged fish as possible were netted and measured. Growth ranged from as little as 1/4 inch to slightly more than 1 inch per year, with an average of 3/4 inch. This confirms other DNR studies showing that adult Mississippi smallmouth grow quite slowly but can live long. (They require 12 years to reach 19 inches.)

The study uncovered a number of important pieces to the smallmouth life-cycle puzzle. The piece that surprised Altena most was how shallow the fish remain during winter. Many biologists had believed that in winter smallmouth invariably relocate to the deepest water they can find. However, many Mississippi fish remained in just 3 to 4 feet of water all winter. This finding is yet another indication that river smallmouth across North America are highly variable in their habits, and likely influenced by river size, type, and geographical location.

Interesting as this new knowledge is, the still-unknowns may be just as tantalizing.

When one smallmouth travels 30 miles and another just three miles, are they returning to the same locations where they had spawned or wintered the year before? An important question and one Altena hopes to answer in the future.

Tim Holschlag, freelance writer and smallmouth bass guide