Growing Fish Food
Establishing native plants in reservoirs feeds fish and keeps out invasive species.
By Larry D. Hodge
A basic rule of thumb states that it takes 10 pounds of food to grow one pound of whatever creature is next up the food chain. That means a 10-pound bass has to eat 100 pounds of baitfish to grow that big.
That simple formula has profound implications for resource managers, for it takes 1,000 pounds of insects and microorganisms to grow those baitfish, and 10,000 pounds of vegetation to grow the insects.
TPWD Inland Fisheries Biologists Mark Webb and Richard Ott are unlikely looking nursemaids, but for the last eight years they have been establishing nursery colonies of native aquatic plants in seven lakes across Texas for just that purpose: to feed the microorganisms and insects that feed the baitfish that feed the big fish.
“The need to do so wasn’t obvious, but it should have been,” says Ott. “When Michael Smart of the U.S. Army Corps of Engineers Lewisville Aquatic Ecosystem Research Facility suggested that we should stock aquatic plants for the same reasons we stock fish, we wanted to kick ourselves for not having seen it. You have to ask yourself when you stock fish, ‘Where will they live?’ and ‘What will they eat?’”
Using grant money from the Corps and from the Federal Aid in Sportfish Restoration Act, Webb and Ott developed techniques to increase the diversity of native plant communities in Texas reservoirs. “We know aquatic plants are essential to game fish,” Ott says. “Native plants have much higher benefit-to-cost ratios than nonnatives, and they won’t take over a whole lake and cause problems, like hydrilla can. As resource managers, we want to select the aquatic species rather than let fate do it.”
The two broke their Statewide Aquatic Habitat Enhancement project into four parts: (1) determine what plants are appropriate; (2) determine what planting techniques and strategies are most cost effective; (3) determine what exclosure designs are most effective and cost effective; and (4) determine the best strategies to deal with water-level fluctuation.
Exclosures — wire pens — are necessary to protect young plants from herbivores like nutria and beavers (as well as turtles and carp) until they can establish themselves and spread beyond the barrier. The design chosen uses a 2-inch by 4-inch mesh that admits small fish and turtles and creates little shading. PVC pipe anchors and tubing supports prevent damage to boats and jet skis if accidentally run over. “We always have to keep in mind that we are working on public bodies of water,” Ott says. “Even after the plants are established, we will keep the exclosures to protect the nursery colonies in case something happens to the plants outside.”
The list of 25 native plants used includes American pondweed, wild celery, water stargrass, coontail, spatterdock, pickerelweed and water pepper. Seventeen do well almost anywhere in Texas. “The function of the plants is to capture sunlight and turn it into food,” Ott explains. “They also provide structure that small fish can hide in and grow, generate oxygen, buffer changes in the pH of the water, slow wave action and filter the water to keep it clearer.”
The native plants have another benefit as well. “If native plants get there first and get well established, they provide resistance to nonnative species,” Ott points out. “It’s like having a good solid lawn that makes it harder for weeds to come up.”
Since almost all large bodies of water in Texas are reservoirs rather than natural lakes, they present a special challenge. “You have to deal with fluctuations in water level in reservoirs,” Ott says. “We’ve had to learn to chase water levels. Plants have to be matched to the water depth and clarity. They have to get sufficient sunlight to grow, but they can’t be so shallow that they will be dry at the times they need to be growing.”
“Plants simply cannot move as quickly as other organisms when the water level drops,” Webb notes. “Our aim is to make sure we have propagules [seeds or tubers] at all levels, ready to germinate and grow when the water comes back up. This is especially important in West Texas lakes, where water levels may fluctuate as much as 20 feet.”
Ott and Webb expect the project to be out of the research stage in about a year. “At that point we can consider it a management technique and use it in different parts of the state,” Ott says. We think this will be a way we can influence levels of recruitment we see in our game fishes. The more plants we have, the more likely we are to have large numbers of predator fish.”
That translates to better fishing for everyone.