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Tennessee's Elk River: Trout vs Boulder Darters

leah kirk

The latest southern trout battleground may be Tennessee’s Elk River. The Elk River below Tims Ford Dam in south-central Tennessee is known for its aquatic diversity. It is home to a wide variety of mussels, snails, and fish, including a number of species protected by the Endangered Species Act. One of these federally listed species is a small fish called a boulder darter.

The problem is, the only known naturally occurring population of boulder darters exists in the Elk River drainage basin. The Elk River is also home to a regionally important trout fishery. Because this is the only natural location of the darter, ESA flunkies have to ensure it can coexist with trout.

The trout fishery, which is stocked by the Tennessee Wildlife Resources Agency, is a put-and-take fishery that is maintained during the summer months by the water released through Tims Ford Dam. When TVA releases water from the dam, it is very cold, due to the depth of the reservoir. Trout thrive in the cold water, but it is too cold for the boulder darter, several endangered mussels that inhabit the tailwater, and warm-water sportfish.

The cold water released when TVA runs the hydropower turbines at the dam for long periods of time can cause a drop in water temperatures many miles downstream of the dam. This change in temperature can stress boulder darters and other warm-water fish, affecting spawning success and growth of young boulder darters. Other native warm-water fish in the Elk River include smallmouth bass and other important sportfish.

After careful study, TVA and the U.S. Fish and Wildlife Service (USF&WS) agreed that TVA would modify its hydropower operations at Tims Ford Dam to warm up the temperature of the tailwater to help protect and promote recovery of the boulder darter and listed mussels. These modifications also should result in improvements to the warm-water recreational fishery in the Elk River. In 2008, TVA began adjusting releases from Tims Ford Dam to provide temperatures suitable for boulder darters, listed mussels, and other warm-water species downstream of the cold-water trout fishery.

Water temperatures are being monitored along the length of the tailwater with the goal of adjusting the operation of Tims Ford Dam to keep water temperatures at the Farris Creek stream gage (Elk River Mile 124) within the targeted temperature range for trout while keeping water temperatures near the Fayetteville stream gage (Elk River Mile 93) similar to seasonal temperatures in free-flowing streams in the region, which can reach the mid-80s (F) during late summer.

The boulder darter was listed as endangered in 1988. The only known wild populations of the boulder darter exist in the Elk River drainage basin, although reintroduction efforts are underway in nearby Shoal Creek, which flows through Lawrence County, Tennessee and Lauderdale County, Alabama. Adult boulder darters are about three inches long and olive to gray in color. As their name implies, boulder darters are typically found in moderately flowing pools or other appropriate habitat areas with current. They are found among large flat rocks relatively clean of silt or where there is large rubble from old collapsed bridge materials.

This highly specific habitat in the Elk River is limited. Boulder darters are present in the vicinity of Fayetteville (ERM 93) and downstream in the Elk River to ERM 30 or 31. Because boulder darters live only two or three years, successful annual reproduction is critical. The darters prefer temperatures between 60-70 degrees Fahrenheit (16-20 degrees Celsius) for spawning and warmer temperatures for the growth of juveniles. Their breeding season is typically May to June.