Drift Dynamics of Post-Hatch White Sturgeon and Estimation of Spawning in the Upper U.S. Portion of the Columbia River during 2012-2013

The subpopulation of White Sturgeon Acipenser transmontanus in the Columbia River between Grand Coulee Dam (Washington) and Hugh Keenleyside Dam (British Columbia) has experienced chronic recruitment failure for nearly 40 years. Past research has documented viable gametes that successfully hatch and begin larval drift.  To understand why recruitment is limiting, larval drift dynamics must be understood. Post-hatch Sturgeon were collected nightly via benthic icthyoplankton nets during 2012-2013. Sturgeon were staged in the field and assigned to three overall stages: early-stage-free-embryo (EFE; stages 36-39); mid-stage-free-embryo (MFE; stages 40-43); and late-stage free-embryo (LFE; stage 44+). Based on larval developmental stage during collection, spawning in 2012 was estimated to occur between June 29^th and August 13^th and between June 10^th and July 15^th in 2013. Peaks in estimated spawning during both years coincided with a descending hydrograph and water temperatures that ranged from 13.2-17.1ºC. We captured 2,071 post-hatch Sturgeon in 2012 (10% EFE, 9.4% MFE and 80.6% LFE) and 4,321 (43.7% EFE, 25.2% MFE and 31.1% LFE) in 2013. Power peaking from upstream dams and raising of Lake Roosevelt to full pool was occurring during larval drift in both years. Ultimately, reservoir operations during larval drift could likely be limiting White Sturgeon recruitment.