White Sturgeon (Acipenser transmontanus) in the upper Columbia River in British Columbia, Canada, was listed as endangered under the federal Species at Risk Act (SARA) in 2006 as the population is undergoing recruitment failure. One segment of the population resides in the Mid-Columbia River, which is a section of the upper Columbia River located between Hugh L. Keenleyside Dam (Castlegar, BC) and Revelstoke Dam (Revelstoke, BC). This small population segment is comprised of approximately 52 adult White Sturgeon (37 – 92 individuals at 95% confidence level) that are older than when the construction of HLK Dam occurred (1969). Natural recruitment to this population has not been identified. In 2007, BC Hydro began an experimental conservation aquaculture program that has released hatchery-reared juvenile White Sturgeon into the Mid-Columbia River. This program has been ongoing in an attempt to evaluate the feasibility of developing either a self-sustaining or failsafe population in this section of the upper Columbia River.
Over the three years, a total of 12 hatchery-origin juvenile White Sturgeon were captured. Half of the captures had survived one winter prior to capture (age 2); the other half were released in the spring of the capture year. Though sample sizes within years are low, growth since release from the hatchery was calculated for all juveniles. On average the age-1 (released in 2013) fish had grown 5.3 cm in length and gained 0.042 kg. The age-2 fish (released in 2012) had grown 11.6 cm in length and 0.193 kg in weight since release. The fish released in 2012 gained weight at a higher rate than those in 2013, on average gaining 0.174 kg/year. Fish from the 2013 year class, however, grew in length at a higher rate compared to the 2012 year class, increasing 15.0 cm/year on average. Only one juvenile sturgeon was captured from the 2014 year class and as such results cannot be compared to other release years. As a result of low capture rates of juvenile White Sturgeon during these study years (2013-2015), increased capture effort is recommended as well as concentrating effort in locations of previous capture.
The main objectives of this study are to 1) describe juvenile White Sturgeon habitat use, including quality and quantity within the Mid-Columbia River, and 2) determine growth and survival of juveniles released from the conservation aquaculture program. These objectives have been assessed in previous years through both direct (capture efforts) and indirect (telemetry) methods, though direct capture was the focus of the study years reported here.
Field sampling was designed to optimize chances of catching juvenile White Sturgeon using previous years’ successes and failures as guidelines. Previous work has also shown that juvenile White Sturgeon within the Columbia River prefer calm, deep (>10 m) areas with fine substrates (Golder 2009b). Additionally, the 2012 acoustic positioning study showed that juvenile White Sturgeon movement is concentrated within the thalweg or in floodplain areas associated with the thalweg, and that movement of juvenile White Sturgeon is greatest early to mid-September (Golder and ONA 2013).
Gillnet and set line sites were established randomly using the general random tessellation stratified (GRTS; Stevens and Olsen 2004) design in R (R Development Core Team). This method provides spatially balanced randomly chosen sample locations. Sites were randomly distributed along the center line of the Mid-Columbia River and distinguished as setline or gill net sites. Over sample sites were also created to replace sites that were rejected during sampling due to logistical concerns (depth, velocity, obstructions) to ensure that randomness and spatial segregation were maintained within the study design. The generated GRTS sites were used as a guideline, and once in the field, sample locations were selected based on targeted water depths (10 – 30 m).
Timing of sampling was targeted in the fall of 2013 (September/October) to coincide with movements (Golder and ONA 2013). Sampling times were expanded over summer and fall (July – October) in both 2014 and 2015 to exploit water temperatures optimal for foraging and expend additional sampling efforts.