Kootenai River white sturgeon: Synthesis of two decades of research

Abstract

Little information is available on the Kootenai River white sturgeon Acipenser transmontanus population prior to the completion of Libby Dam (Montana, USA) in 1972. Regulation of the Kootenai River by the dam significantly lowered discharge and reduced river temperatures during the white sturgeon spawning season. The population became recruitment limited and was listed as endangered under the US Endangered Species Act in 1994. An international recovery team between the USA and Canada was formed to develop a recovery plan and recommend recovery measures. This paper is a synthesis of research that followed. Population studies estimated an abundance of 1000 adults declining at about 4% annually. Through conservation culture hatchery stockings in the early 1990s, survival was found to be about 65% in the first year and 90% thereafter; consequently, hatchery fish soon dominated the population. Wild white sturgeon spawning occurred in spring when the river warmed to ≥8°C but took place over sand substrates which were thought to be unsuitable for incubation and rearing. Recruitment failures continued to drive the decline despite augmented discharge, which was of little value to white sturgeon spawning. Evaluation of spawning habitat and fluvial processes confirmed that cobbles and gravels were present at most spawning locations but were buried under sediment. Although discharges ≥1600 m 3 s -1 for a period of 2 wk would likely scour fine substrates and provide more suitable spawning and rearing conditions, such a measure would be socially and politically unacceptable. Thus, support should be given to a habitat management plan that restores suitable substrates that help promote enhanced survival of embryos and larvae. © Inter-Research 2012.