Cooperative Fish and Wildlife Research Units Program: Montana Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Recruitment of White Sturgeon in the Transboundary Recovery Area (TRA) of the Columbia River [Hugh L. Keenleyside Dam (HLK) to Grand Coulee Dam (GCD) in WA, USA] has not occurred at a rate sufficient over the past 40 years to maintain the population going forward. Conservation aquaculture has become a critical component of recovery programs, including for White Sturgeon (Acipenser transmontanus) in the lower Columbia River where extirpation has largely been avoided due to the success of hatchery-origin juveniles released into the wild. Survival of hatchery-origin juveniles in the upper Columbia River population has been higher than originally predicted, with more than 30,000 individuals estimated to be at large in the population (BC Hydro 2016a). Within the hatchery population, certain year classes are estimated to be in higher abundance than the existing wild population (~3,000 mature individuals), as a result of higher survival for year classes released at larger body size. Of further concern, within year class genetic diversity has been estimated to be reduced relative to the time of release from the hatchery (McLellan and Crossman unpublished data) as a result of disproportionate survival among maternal family groups. As a result of these findings, there is an urgent need to determine when the hatchery population will mature and begin contributing to natural spawning, as genetic swamping of the existing wild population is a risk given numbers of estimated annual breeders (121.5 ± 34.7 adults (mean ± SD); Jay et al. 2014). In the wild, White Sturgeon begin maturing between the ages of 15-35 years for females and 10-12 years for males (PSMFC 1992; Billard and Lecointre 2001). When provided with conditions for maximum growth in captivity, sexual maturity can occur much earlier with males maturing as early as 3 years of age and females as early as 6 years of age (Doroshov et al. 1997) However, age at first maturity is not well documented for hatchery-origin fish in productive systems like the lower Columbia River, Canada, where growth rates are high following release into the wild and individuals are reaching a body size similar to mature adults by age 14 (BC Hydro 2016b). The hatchery population in the lower Columbia River, Canada, represents a unique opportunity to determine age and size at first maturity in hatchery-origin fish, whether the hatchery-origin fish differ in reproductive indices (Table 1) compared to wild fish, and how other variables (e.g. habitat use or environmental covariates) may influence when individuals become reproductive. This information, in combination with other ongoing monitoring, will help inform both long-term population targets and ongoing revisions to numbers of fish that are released annually from the conservation aquaculture program. Sturgeon females and males are not sexual dimorphic (Billard and Lecointre, 2001). There are several available methods to assess sex and stage of maturity in sturgeons (Webb and Van Eenennaam 2015), though direct comparison among all methods (ultrasound, endoscopy, measurement of plasma sex steroids, and biopsy) in their efficiency and reliability in assigning sex and stage of maturity are limited. Additionally, certain methods are more invasive than others limiting what may be possible for threatened or endangered populations where permitting requirements focus only on noninvasive techniques, and the most accurate method(s) that may be applied to females to assess sex and stage of maturity may differ from those that may be applied to males. This further supports the need for comparative assessments between available methods for females and males and, given the endangered status of sturgeon species globally, is applicable beyond White Sturgeon.