Evaluation of Recovery Goals for Endangered White Sturgeon in the Kootenai River, Idaho

Abstract

Our objective was to evaluate recovery goals for endangered white sturgeon Acipencer transmontanus in the Kootenai River, Idaho. We used demographic statistics for white sturgeon in the Kootenai River in a stochastic density-dependent population model to estimate recruitment rates needed for population recovery. We simulated future abundance of white sturgeon in the Kootenai River over a 25-year period and a range of hypothetical recruitment rates to estimate the level of recruitment that would lead to population recovery (7,000 fish, the number present before the population suffered recruitment failure). We compared simulations of future abundance at enhanced levels of recruitment with those based on the present status of the population and with the recruitment criterion in the Kootenai River White Sturgeon Recovery Plan. We found that the population would decline to only 57 individuals after 25 years and only 6 individuals after 50 years if recruitment failure continued. The population would reach the target carrying capacity of 7,000 individuals within 25 years only when each adult produced 0.4 age-1 recruits, a recruitment rate equivalent to reaching the target level of recruitment in the recovery plan every year. In contrast, the population would grow to only 1,200 individuals if the target level of recruitment in the recovery plan was produced in only 3 of every 10 years, as specified in the recovery plan. We suggest that recovery goals for white sturgeon in the Kootenai River can be modified as follows: (1) a population goal of 7,000 subadults and adults; (2) population recovery within 25 years; and (3) a minimum recruitment rate of at least 20 age-1 juveniles detected from each year-class in each of 10 years by use of a standardized monitoring protocol.