The Missouri Department of Conservation has many methods for tracking the health and reproduction of fish populations throughout waterways in Missouri.
Earlier this week, department staff used electrofishing to check the current state of the fish at the Savannah City Lake.
“Electrofishing is used because we can sample a large number of fish in a short period of time without hurting the fish,” Biologist Tory Mason said. “We could use gill nets, for instance, but that can kill the fish.”
Electrofishing entails using two electrodes that deliver a direct current into the water. The current causes an uncontrolled muscular convulsion in the fish called galvanotaxis. This normally results in the fish swimming towards anode.
Once the fish is shocked, it will float near the top of the water and is then dipped out with a net. The fish is placed in oxygenated water until it can be measured and then placed back in the water.
“The information we obtain from each sample shows us the number of fish per hour of electrofishing,” Mason said. “It gives us size indices (percentage of fish of a certain size) and we enter the data into a database. This allows us to compare years or several years of data and shows us trends.
“An example is a very fast negative trend in number of bass per hour on a certain lake,” he said. “We then might want to look at changing the regulation to protect the bass.”
Staff members focus on the size and shape of fish like bass and bluegill. Those populations tend to repopulate at a high rate unlike channel catfish. The department hatchery will grow the catfish to a certain size before they’re placed in lakes like Savannah. This is due to bass eating the younger, smaller catfish.
The biologists use trees and other shrubbery placed in the lake as hot spots for fish.
“We add trees in the fall, winter and early spring when we’re not as busy sampling,” Mason said. “We put brush in shallow water to provide cover for small fish to get away from predators and attract fish to shoreline access for shore anglers. We also put deeper brush in to attract fish and provide good habitat in deeper water for fall and winter fishing.”
Mason pointed to the numerous ways electroshocking helps protect lakes and rivers, but said they’re still asked to defend the study. Mason said that he recently was asked by his superiors what was gained by spending days traveling from place to place.
“We sample to be better informed of our fisheries or to have the data to change a regulation or to notice an invasive species like carp or gizzard shad,” Mason said. “The more we know and can tell the public, the better the fishing will be for anglers that fish Missouri.”