Restoring riparian shade along some of Missouri’s smaller spring-fed Ozark streams will likely benefit adult smallmouth bass growth and influence population sizes, University of Missouri researchers have found.

Indications are that the smallmouth bass numbers have been in decline during the past 30 years, said Charles Rabeni, Missouri Cooperative Fish and Wildlife Research Unit leader.

“We want to see what we can do to help restore the smallmouth bass populations,” he said.

Lab experiments indicated that the popular game fish fares better when water temperatures do not exceed 80 to 82 degrees.

Field surveys and models indicate that one key to keeping water cooler in streams is increased shade from riparian forestation, particularly along the many miles of smaller spring-fed streams throughout the area, said Rabeni.

Adult smallmouth bass in streams fed by warmer surface water have lower growth potential during summer than fish in ground-fed streams, and they are subject to body-mass loss when stream temperatures exceed 82 degrees.

“A couple degrees difference in the summer can make a big difference whether a fish is doing well or not,” he said.

As temperatures go up, fish will eat more and grow, but there is a point where that drops off considerably, he said.

Riparian restoration and management is expensive and should focus on places where it will do the most good. If better smallmouth bass population is the goal, restoration should be made in selected areas. Streams not fed by groundwater consist of runoff surface water, which is warm to begin with, so riparian vegetation would not make that much difference in making it cooler, he said.

Rabeni’s research unit studied the smallmouth bass because it is a top predator, influenced by all the species below it in the food chain. That makes it a good environmental indicator. It is a popular sports fish, one the public understands and sensitive to human activities on the land, he said.

“We’ve been interested in the Ozark streams for a number of years because of the historical problems we find there and as well as some new ones,” he said.

The public may consider those Ozark streams to be pristine, but in fact they are not. Some of the species in those waters are in a bit of a bind due to factors in addition to water temperature, he said.

Channelization, gravel and lead mining, and livestock in the streams create environmental problems. Keeping livestock out of the streams by providing separate watering sources could be a major step in improving water quality by reducing siltation and bacteria counts.

“We have a situation in the state where the streams need a lot of work. We want to put our money and resources where they will do the most good,” he said.

Popular fishing areas, such as along the Jacks Fork River, still have nice smallmouth bass populations, but once you get away from such focus centers you see that small land-use changes resulting in things like bank erosion can tip the balance on them, he said.

The smallmouth bass is a slow-growing fish requiring five to six years to reach a length of 12 inches and weight of about a pound.

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