July 2020 | by Jeff Finley
We at the U.S. Fish and Wildlife Service work to conserve some of the rarest plants and animals in the country. The conservation effort to restore the Niangua darter, an endangered fish found only in central Missouri, has brought safer bridges to rural communities. The story of the Niangua darter demonstrates how the work of the Service’s National Fish Passage Program directly benefits the American public we serve.
The Niangua River winds northward through central Missouri, due south of the Lake of the Ozarks. Swimming along the bottom of the river lives a small fish, aptly named the Niangua darter. Native to the north- flowing tributaries to the Osage River and found nowhere else in the world, the fish is listed as a federally threatened species and as state endangered by Missouri.
The decline of the Niangua darter is due in part to an evolutionary peculiarity. About the size of your pinky finger when fully grown, darters lack a swim bladder, the pocket of air used by most fish to float. That means they spend their life darting between rocks along the bottom of central Missouri’s rivers and streams. A colorful fish, the markings on males become brilliant when spawning, displaying bright red and green bars on their sides, a red rim to their dorsal fin and a brilliant orange belly. Both males and females have two distinct black dots, similar to eyespots that many butterflies bear, marking the base of their tail.
“We care about the Niangua darter because it is sensitive to changes in water quality, such as excessive sediment and nutrients,” explained Craig Fuller, a fisheries management biologist with the Missouri Department of Conservation. “The disappearance of the Niangua darter was an early warning sign that something was wrong on the landscape that was negatively impacting the health of the river.”
As humans reshaped the Niangua River to develop hydroelectric power, the Niangua darter’s home was broken into pieces. The first major manmade barrier fragmenting the watershed was Tunnel Dam, located on a map just north of White City, Missouri. The project was a primary example of how hydroelectric dams alter the flow of rivers. When completed in 1930, the dam elevated water levels to divert the river through a 500 foot-long modified cave, which then redirected the flow through a 3-megawatt generator, before it was reconnected to a bend farther downstream. Tunnel Dam was the first of many 20th century hydroelectric engineering projects that powered the economic growth and development of central Missouri, and subsequently marked the decline of the darter. The dams alone were not to blame for the darter’s disappearance. As more people moved to the area, more roads were built, and with them came many poorly designed low-water stream crossings. It is here that the lack of a swim bladder became detrimental to the Niangua darter.
Low-water stream crossings are where roads and streams intersect. They are often found in rural America as they are ideal for low-traffic use. When poorly designed, they may act like a small dam and hinder the natural function of a stream, as well as pose a safety hazard to people. Poorly designed low-water stream crossings create an unnatural fall, or perch, downstream as culverts clog or are damaged as floodwaters scour a pool. This alters the natural shape of the river bed and makes it difficult for a tiny fish without a swim bladder to navigate. Additionally, scoured out crossings pose a drowning hazard for people since vehicles can be washed away when trying to use these crossings when flooded. When this occurs, local residents no longer have safe transit for school buses, mail carriers and emergency vehicles during moderate floods.
By the early 1980s, conservationists began to detect declines in the number of Niangua darters and a stagnation in genetic diversity. Once abundant, Niangua darter populations were found in only eight streams. Niangua darter habitat restoration was largely triggered by “A Recovery Plan for the Niangua Darter” published by William Pflieger in 1989. The plan’s findings were later augmented by the Missouri Department of Conservation’s Niangua Darter Recovery Team, who added low water stream crossings as a central cause for decline.
In 2002, the Missouri Department of Conservation conducted a low-water stream crossing survey across the Niangua darter’s remaining eight native watersheds. It was determined that of the 50 crossings in the Niangua darter’s range, 34 were barriers to the darter’s movement. The barriers prevented the Niangua darter from accessing upstream spawning and feeding habitats. Each flood washed darters downstream, or if they migrated downstream, they were unable to return to the upstream habitats once waters receded.
“The Niangua darter is a perfect example of why the National Fish Passage Program was created,” said Jessica Hogrefe, U.S. Fish and Wildlife Service National Fish Passage coordinator for the Great Lakes Region. “Our partners knew that barriers were the root cause for the darter’s decline, but due to the sheer number of barriers in the fish’s range, they needed federal support to take on the removal projects.”
For funding assistance in removing the barriers, the Missouri Department of Conservation collaborated with the U.S. Fish and Wildlife Service’s National Fish Passage Program through the Columbia Fish and Wildlife Conservation Office. The National Fish Passage Program works with local communities on a voluntary basis to restore rivers and conserve the country’s freshwater resources by removing or bypassing barriers. National Fish Passage Program projects benefit both fish and people as the Service works with local partners to remove obsolete and dangerous dams, permanently eliminating public safety hazards and restoring rivers to their natural state.
In 2004, the Niangua Darter Recovery Team began to systematically remove low-water stream crossings impeding the movement of the Niangua darter and replace them with clear span bridges. Unlike low-water stream crossings which are partially in the water, a clear span bridge places the bridge pilings outside of the stream channel where possible, which allows for the free movement of freshwater organisms and restores the natural flow of water and sediment. In addition to being fish friendly, the new bridges are easier to maintain and safer for people to use during moderate flood events.
As noted in 2007 by Lance Hutton, then a member of the Hickory County Commission, “Replacing that crossing [in Hickory County] was something that we had anticipated for several years, but, just couldn’t afford it. The Fish and Wildlife Service made that possible…That old crossing was a very dangerous situation. Now, all the comments I get from the people that live in that area and hunters, fisherman, and campers that use the river are very positive. It’s been a really good thing for the county.”
To date, the Missouri Department of Conservation, the Columbia Fish and Wildlife Conservation Office and various county commissions have successfully replaced 29 stream crossings within the native range of the Niangua darter. Annual fish monitoring reveals Niangua darter populations are starting to stabilize and improve, along with other native fish species. The story of the Niangua darter demonstrates how the Service’s National Fish Passage Program supports local partners to spur action for the benefit of native fish and the surrounding communities.