When we think of the Missouri River in South Dakota today, we likely picture huge reservoirs suitable for boating, water-skiing and angling for walleyes. But it wasn’t long ago that the Missouri was a wild, braided river, moving and depositing soils and creating diverse habitats for its array of fish and wildlife species. And while we may appreciate the opportunities of the reservoir system, we shouldn’t lose sight of what was forfeited with this massive conversion of riverine habitat. As Mark Twain said: "A river without islands is like a woman without hair. She may be good and pure, but one doesn't fall in love with her very often."

Two minnow species were among the victims of the Missouri River’s conversion – the sturgeon chub (Macrhybopsis gelida) and sicklefin chub (Macrhybopsis meeki). Although recently removed from the list of species considered for federal endangered or threatened listing, their distributions are much reduced from historical times.

The sturgeon chub once inhabited the Yellowstone River, the Missouri River, the Mississippi River downstream from the mouth of the Missouri, and many of the large tributaries of the Yellowstone and Missouri rivers. Its South Dakota range included the Little Missouri River and the Missouri River and its western tributaries - the Grand, Cheyenne, and White rivers. The sicklefin chub had a somewhat similar historical distribution, living in the Yellowstone and Missouri rivers and the Mississippi downstream from the mouth of the Missouri. The sicklefin did not range into the large tributaries of the Yellowstone and Missouri.

Form follows function, as the cliché goes, and the physical characteristics of these species are well suited for life in the "Big Muddy." The Missouri River historically carried a heavy silt load, collected from tributaries in the northern part of its drainage. Its wide and diverging channel created shifting sandy islands, spits, and pools, and fish species that evolved in the Missouri were suited to its turbid and dynamic conditions.

The sturgeon chub has a streamlined body, small eyes, a small mouth with a barbel at each corner, and a long flattened snout. Its head, body, and fins have scattered external taste buds, likely an aid in locating food. Scales have keeled ridges, possibly to improve orientation in murky waters. The sicklefin chub’s adaptations for life in the Missouri include reduced eyes and external taste buds, presumably to help find food by taste. General habitat needs are similar for these two species – large, turbid river channels that have a strong current, riffle areas, and a sand or fine gravel substrate.

Very little is known about basic life history attributes. The sturgeon chub may become sexually mature at age 2 and likely lives only to age 3. It may spawn primarily during June and July. The sicklefin chub is also short-lived and is thought to be a spring-spawner. Food habits are also poorly known. The sicklefin chub has taste buds both on the outside of its body and inside its mouth, leading scientists to speculate that it may take in an assortment of material while feeding on the river bottom and then sort edible from inedible material.

With each new project to dam, channelize, and otherwise "control" the Missouri River came a loss of the habitats these chubs depended on. Deep, clear waters with more predictable flows and stable water levels replaced the formerly dynamic, silt-laden flows. The sturgeon chub is absent from the Missouri River reservoirs and from many of the formerly inhabited tributaries of the Missouri and Yellowstone rivers. The sicklefin chub is also gone from the Missouri River reservoirs, and its status elsewhere is uncertain.

In evaluating whether to add these species to the list of federal threatened or endangered species, the U.S. Fish and Wildlife Service determined that the sicklefin chub now inhabits 54% of its historical range, and the sturgeon chub is presently found in 55% of its historical range. The Service theorized that since these species have survived to date in the face of such dramatic habitat changes, their future is likely secure.

But questions remain. Is 54-55% of remaining historical habitat within the Missouri River Basin enough? Are the remaining populations thriving or just holding their own? How can fisheries scientists manage for species for which so much is unknown?