Effectiveness of Artificial Substrate in Capturing and Retaining Sturgeon Eggs

Over the past 50 years, there has been a well-documented collapse in white sturgeon recruitment in the Kootenai River, and white sturgeon has been listed as an endangered species since 1994. Libby Dam, constructed along the Kootenai River in northwest Montana, started operation in 1974, which is believed to be the last successful year for white sturgeon recruitment. Lack of appropriate spawning substrate is thought to be a primary factor responsible for white sturgeon population recruitment failure. White sturgeon are broadcast spawners that release adhesive, negatively buoyant eggs that sink to the riverbed. Three- to six-foot sand waves (or dunes) now exist in the reach where spawning occurs. Available information suggests that suffocation and high egg mortality occur where the bed is composed of shifting sand substrate. A Substrate Enhancement Pilot Project Implementation Plan was developed by the Seattle District, U.S. Army Corps of Engineers, to test the effectiveness of various types of artificial substrate for improving spawning success in the reach downstream of Libby Dam. 1:20 Froude-scale physical modeling of different artificial substrate designs was conducted at the Colorado State University Hydraulics Laboratory. This investigation involved three separate tests of rock riprap placed as a mass on the riverbed that projected above the effects of the sand waves. This paper presents an analysis of the flow velocities and turbulent Reynolds stresses that developed over the surface of each artificial substrate. In addition, an evaluation of the effectiveness of each substrate to trap and retain sturgeon eggs is presented.