Unraveling the Mystery of the Kootenai River White Sturgeon

By: Vaughn Paragamian, Principal Fishery Research Biolosist, Idaho Department of Fish and Game and Gary Barton, US Geological Survey Sturgeon have remained unchanged for over 175 million years. They outlasted the dinosaurs and many mammals that went extinct after the last ice age. However, sturgeon are now in trouble world-wide, and many of their problems are due to the fact man has drastically changed the living conditions in waters inhabited by sturgeon. The Kootenai River white sturgeon; found in Idaho, Montana and British Columbia, is one of the sturgeon species in serious peril. Many changes have taken place in the Kootenai River, the most dramatic when Libby Dam in Montana turned it into a regulated river. Seasonal flows are much different than they were naturally. The Kootenai River white sturgeon was listed in 1994 as an Endangered Species. Since then, the US Army Corps of Engineers has manipulated flow levels with the intent of enhancing spawning and rearing. The flows were initially thought to be a "silver bullet"... the answer to recovery. Although fishery managers would prefer higher and more consistent river flows, white sturgeon spawn in the Kootenai River. Idaho Department of Fish and Game (IDFG) researchers have found over 1,500 eggs since the flows were adjusted for sturgeon. However, there is very little evidence the eggs are surviving beyond three weeks. The Kootenai Tribe of Idaho is producing hatchery fish by artificially spawning wild sturgeon. These fish are being released at about seven inches in length and they are surviving well. Herein lies a mystery, a mystery that fisheries researchers are trying to solve. Why are the hatchery fish surviving while the eggs produced by wild fish are apparently perishing? One very important reason may be that white sturgeon are now spawning over a sand bottom in the Kootenai River. When first produced, sturgeon eggs are adhesive. They sink, and are designed to attach to cobble and gravel bottom types. These types of bottoms are usually secure and don't move much. In the Kootenai River, the current spawning location of white sturgeon is a sand substrate rather than a gravel substrate. The sandy bottom areas of the Kootenai are like large, wind blown sand dunes. Instead of being created by wind, however, these dunes' are created by water currents. Upstream from where the sturgeon are now spawning (around Bonners Ferry), there is suitable cobble and gravel substrate. The substrate gets better the further upstream you go. IDFG researchers believe that there was an important change in the river that was unexpected and has received little notice. When Libby Dam was built, a power company in Canada began to operate a dam at the outlet of Kootenay Lake differently than before. They artificially lower the lake just before sturgeon spawn. While sturgeon are spawning the lake elevation is lowered. IDFG researchers have found as the lake elevation raises with inflowing spring water the sturgeon move further upstream to spawn. But they never reach good spawning habitat. The elevation changes in Kootenay Lake change the velocities in the very low gradient river. IDFG researchers believe the spawning sturgeon are keying in on specific velocities and follow these velocities upstream as the lake elevation changes. If the researcher can determine why sturgeon are spawning where they are, it could open the door to one of several measures to recover sturgeon and bring them back to a fishable level. Some of the measures could be improving the habitat where the sturgeon are spawning, or rehabilitating the historic spawning area (this is thought to be a reach of river in the vicinity of Bonners Ferry). The US Geological Survey (USGS) has some very sophisticated equipment for studying rivers. The USGS is now helping the IDFG and the Kootenai Tribe of Idaho with a study of the river, including water velocities, river flow, river stage (height), sediment transportation, and lake elevations to determine how these changes can affect white sturgeon spawning locations. The principal objective of the proposed study is to (1) improve the understanding of the sediment transport-processes in white sturgeon spawning habitat, and (2) develop computer models to assess concepts of these processes and to evaluate the feasibility and potential effects of proposed recovery actions on spawning substrate conditions. The objectives and scope of this proposed project will provide appropriate and valid scientific information to the White Sturgeon Recovery Team's adaptive management decision process. The intent is to determine whether or not to implement substrate enhancement measures in the spawning reach or rehabilitate the historic location. Studies were started in 2002 and progress by the USGS is being made. Bathymetric mapping is being conducted in the white sturgeon spawning reach and upstream of Bonners Ferry to Libby Dam. Sediment sampling in the river is being conducted during the different flow releases from Libby Dam. Stream-velocity (feet per second) and stream-flow (cubic-feet per second) measurements were made and the suspended-sediment in the water column of the Kootenai River was sampled . These suspended-sediment samples were collected under a range of river flows and analyzed for concentration and particle-size distribution. A USGS sediment modeler has begun constructing multi-dimensional models to simulate sediment transport in the white sturgeon spawning reach. These models will be used to assess the feasibility of improving the substrate where white sturgeon spawn. There are no "silver bullets" to recovering white sturgeon but the answer to the mysteries are right around the corner. It will take time and effort. There is good reason to hope that the white sturgeon in the Kootenai River will continue to persist for another 175 million years.