Spring Creek Study

Spawning 

Studies

The latest investigation examines effects of herbicides sprayed on spawning bass. The best time to spray herbicides on aquatic plants is in early spring, just as they begin to grow. In northern states, this coincides with the spawning period of bass and other fish. As a result, spraying often occurs during the spawn, which has led many anglers to fear that it harms recruitment.

To test this theory, we placed largemouth bass in six ponds at Auburn University with dense aquatic vegetation, waited for them to build nests and begin spawning, then sprayed either herbicide or water directly over the spawning beds. We observed their behavior over the next 12 hours, then over the next 30 days to see if they abandoned nests. We also checked bass and bluegill reproductive success in ponds that were sprayed with herbicide and others sprayed with water.

After two years, we haven’t detected changes in bass behavior or in reproduction of bass or bluegill between the two treatments. 

This research has demonstrated no adverse effects of herbicide spraying on behavior of largemouth bass, which made only subtle changes in adapting to the altered but more natural ­environments. They didn’t respond to the spraying process, whether it was done by airboat over expansive hydrilla beds or with a hand-held sprayer while they guarded nests in a shallow pond. Rather than blaming biologists and herbicide spraying ­programs for their lack of success, anglers may want to follow the example of Kiriyama and ­others, who adapted to the changes in habitat and remained successful.

If an aquatic vegetation control program is proposed for your favorite lake, understand that many of the “evils” attributed to these programs may be matters of perception, not fact. Bass and other fish do not pack up and head out at the first sign of an airboat spraying herbicides. Anglers have proven time and again that you can still catch fish from areas that have been sprayed with herbicides. By adapting new tactics tailored to the altered habitat, you may catch more bass than you did when vegetation was dense.

With the continued spread of exotic plants such as hydrilla and Eurasian water milfoil, and given the arrival of new ones like giant salvinia, aquatic plant control remains a priority for lake and reservoir managers across the country. Anglers should work with biologists to reach solutions that all user groups can live with, and compromise may be essential for overall success.

A case in point: At famous Lake Guntersville in Alabama, Tennessee Valley Authority managers determined that maximum recreational value occurs with plant coverage of about 18 percent of the reservoir. When coverage is greater, value declines from loss of recreational boaters and swimmers, who then visit other lakes, instead. With plant coverage less than 18 percent, the lake’s value falls as anglers depart for weedier waters.

Debate over herbicide use is sure to continue as exotic plants spread and fluorish. While bass anglers and other user groups like water-skiers differ on preferred plant coverage, discussions and management decisions should be based on the best available research.  

Dr. Steven M. Sammons is a research fellow at Auburn University and has conducted fishery research throughout the Southeast and Midwest.