Application of a Standardized Gillnetting Method to Assess Cohort Strength in a Depressed Lake Sturgeon Population in the Nelson River, Canada: Implications for Impact Assessment, Development of Mitigation Strategies and Monitoring

Many of the rivers inhabited by Lake Sturgeon have been and continue to be coveted for hydroelectric development. Although habitat alterations can be predicted/quantified, assessment of impacts and development of mitigation strategies is complicated both by depressed population levels (influenced by over-exploitation), and logistic issues associated with sampling in large, torrid rivers. A standardized gillnetting method, focused on sampling juveniles (age 1 – 10 years), was used to assess cohort strength in a depressed population located upstream and downstream of the proposed Keeyask hydroelectric generating station (GS) in the Nelson River, Manitoba. Results suggest similar cohort frequency distributions both upstream and downstream of the proposed GS axis. In both areas, over the three successive years of sampling (2010 – 2012), a single strong cohort (2008) dominated the catch while the remaining cohorts were weakly represented. Correlations to abiotic predictors (flow, air temperature, etc.) identified in other locations, do not explain the observed recruitment pattern. Pending receipt of regulatory approvals, construction of the Keeyask GS may begin as early as 2014. The development of mitigation strategies and monitoring plans for the project considered the current state of the population and included a stocking program and habitat remediation.