Plastic in lakes? Not bad

These Georgia cubes were similar to those used in a Texas study of fish attractors. (Photo by Tim Bonvechio)

When I saw the old-but-newly-acquired fix-r-upper vessel parked in his yard, I asked my bass-fishing buddy, “Hey Ben, what’s the pontoon boat for?”

“Habitat barge,” he replied. “I’ll use it to install brush piles.”

Ben is a maestro at extracting bass and other sportfish from brush piles, so the more the better. Adding brush piles to favorite waters is a common practice — although labor-intensive — for many anglers. And when done with some forethought, it is probably a good thing for Mississippi’s reservoirs, which are increasingly devoid of habitat.

A Texas study proved that crappie are attracted to plastic fish attractors. (Photo by Don Gabelhouse)

Habitat enhancement in reservoirs is getting a lot of attention from fisheries agencies nationwide.  As reservoirs age, woody habitat — brush, logs, standing timber— decomposes. Several studies have clearly demonstrated the importance of woody habitat to productive fish populations, and many more studies have documented the benefit of installed woody habitat to angler catch.

In other words, wood is good.

Learning by doing

Adding habitat to aging reservoirs is far from a new idea. Years ago, many studies reported on the effects of adding woody habitat. Some reported that different fish species had preferences for different types of sunken trees and brush, for example, pine vs. cedar vs. hardwoods. I think the “wisdom” gained from these studies is that where the woody habitat is placed and the interstitial spaces — the sizes and amounts of nooks and crannies — has more to do with what fish and what sizes are most attracted.

Years ago, the Tennessee Valley Authority installed many extensive fish attractors in Pickwick and other TVA impoundments. Long before GPS, the fish attractors were marked with telephone poles pushed into the bottom. At least some of the telephone poles are still there, but the sunken brush is long gone. Decomposition is a problem with all added woody habitat. How long the brush lasts and remains effective varies depending on the type and size of wood. Repurposed Christmas trees may attract fish for only one or two years.  Hardwoods tops with thick limbs last longer, but bigger and heavier woody habitat creates deployment problems.

Plastic attractors

While Ben’s habitat barge may suffice for enhancing his secret fishing holes, deployment of fish attractors on a large scale is time-consuming and requires a serious upgrade in equipment. Given these costs, longer-lasting and more-durable plastic fish attractors, even though expensive to buy or build, may be more economical in the long run.

A study at Sam Rayburn Lake conducted by fisheries biologists with the Texas Parks and Wildlife Department compared fishes’ attraction to PVC pipe-framed cubes filled with corrugated polyethylene drain pipe or plastic mesh. The frames filled with drain pipe are often called “Georgia cubes.”  Several years ago, biologists with the Georgia Department of Natural Resources found the cubes attracted species and numbers of fish similar to woody habitat during the first 2 years after deployment. By Year 3, however, the cubes attracted four times as many fish as the woody habitat, largely due to decomposition of the wood.

The attractors used in the Texas trials were 3x3x6 foot frames made of 1½- or 2-inch diameter PVC pipe. The corrugated pipe or plastic mesh was wound around the frames. Holes drilled in the frame facilitated sinking.

PVC-pipe fish attractors with plastic mesh (left) and drain pipe were part of a study in Texas’s Sam Rayburn Reservoir. (Photo by Todd Driscoll)

Multiple groups of six structures of each type were placed either in a line or in clusters in water 16 to 20 feet deep — above the metalimnion but deep enough to ensure that they would remain in relatively deep water if the reservoir level fluctuated. All were put in areas devoid of cover but with other fish-attracting features, like underwater points of adjacent to steep contour breaks. Fish use of the structures was monitored by divers and fixed underwater cameras in 2014 and 2016.

The results

The drain-pipe structure attracted more species and greater numbers of all species combined than the mesh structures. The drain pipe structure had more black crappie, bluegill and longear sunfish; the mesh structures had greater numbers of largemouth and spotted bass.

The configuration of the structures —arranged linearly or in a cluster — did not affect abundance of any species.

Corrosion of the hardware used to attach the structures to anchors resulted in the buoyant mesh structures floating to the surface — the plastic mesh is buoyant; the corrugated pipe structures remained on the bottom. Using only data from the pipe structures, abundance was greater in 2014 than 2016.

Take-home message

Plastic structure works. For a long time. Low maintenance, but use corrosion-resistant cables and cable clamps to anchor the structures.

The greater attraction to the structures in 2014 than 2016 remains a bit of a mystery. More fish were expected in 2016, because Rayburn had less hydrilla in 2016, and the structures had a longer time to be colonized by algae and invertebrates.  Diver observations, however, confirmed that these structures were quickly colonized by algae and invertebrates. A likely reason for the declining fish abundance was that these structures had been discovered by anglers, and fish had been harvested.

Interested in using fish- and angler-friendly plastic fish attractors or maybe encouraging a habitat-enhancement project with the Mississippi Department of Wildlife, Fisheries and Parks? The attractors used by TPWD cost (in 2014) $125 to $175 for each pipe structure and $60 for each mesh structure.

Regardless of what kind of fish attractor you place in Mississippi’s public waters, contact your district fisheries biologist to discuss any restrictions or permit requirements.

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About Hal Schramm 172 Articles
Hal Schramm is an avid angler and veteran fisheries biologist.

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