Many people think that turtles are detrimental to fish populations and believe they need to be removed from impoundments. However, the many species of turtles in southern Oklahoma and northern Texas have varied diets and none of them are exclusively fish.
There are four families of turtles in Oklahoma made up of 17 species, of which 15 are considered aquatic. The families are Chelydridae (snapping turtles), Kinosternidae (mud turtles and musk turtles), Emydidae (map turtles, box turtles, cooters and sliders) and Trionychidae (soft-shelled turtles). Food habit studies have shown that most aquatic turtles are opportunistic eaters, meaning they eat what they can. Most turtles are not efficient fish predators, so they seldom catch healthy adult fish.
Red-eared slider (most easily identified by the red patch behind the eye) is probably the most common and abundant turtle in ponds in southern Oklahoma and northern Texas. As a juvenile, its diet consists of more animal matter, such as insects, crawfish, snails, tadpoles and juvenile fish, than plant matter. As it grows to adulthood, its diet typically consists of approximately 90 percent vegetation. Most of our aquatic turtles have diets similar to the red-eared slider. However, snapping turtles and soft-shelled turtles eat more animal matter than the red-eared slider.
Snapping turtles are omnivorous and eat insects, crayfish, snails, amphibians, fish, reptiles, birds, mammals and vegetation. There are two species of snapping turtles (common and alligator) in southern Oklahoma and northern Texas. The common snapping turtle is widespread and found in many small impoundments; however, it is rarely found in numbers large enough to impact fish populations. The alligator snapping turtle is usually found in backwater sloughs in the eastern third of Oklahoma and Texas.
There are two species of soft-shelled turtles (smooth and spiny) in Oklahoma. Their diets primarily consist of earthworms, mollusks, crayfish, amphibians, fish and vegetation. Soft-shelled turtles are usually found in streams and rivers, but sometimes can be found in small impoundments.
In Alabama, researchers stocked four ponds in the spring with fingerling bass and bluegill. Two of the ponds were also stocked with 100 sliders per acre. All ponds were managed identically for the duration of the study. In the fall of the same year, the ponds were drained and total fish biomass was recorded. There was no significant difference in fish biomass between the ponds with turtles and the ponds without. Additionally, the stomachs of 58 turtles from the study were examined; 80 percent of their diet was comprised of vegetation and less than 3 percent was fish.
If a pond manager wants to establish aquatic vegetation in an impoundment for waterfowl, recreational fishing, aesthetics or any other reason, turtles may need to be controlled in some cases. For example, red-eared sliders can become so abundant in ponds that they can prevent some submersed aquatic plants from becoming established. If a pond manager wants to establish plants, turtle exclosures should be placed around the plantings until they become well established. Turtles could be trapped in order to temporarily reduce turtle numbers and the amount of newly established vegetation consumed. Consult local game laws before trapping turtles.
As part of the natural ecosystem, turtles add value to a pond. They help consume carrion that may be in a pond. Most aquatic turtles in southern Oklahoma and northern Texas are not efficient predators of fish; the species that predate fish usually are not abundant enough to impact fish populations.
Moss, Don. 1955. The Effect of the Slider Turtle "Pseudemys scripta scripta" (Schoepff) on the Production of Fish in Farm Ponds. Proceedings of the Southeastern Association of Game and Fish Commissioners Meeting. p. 97-100.