Cohort-specific estimates of first-year survival are positively associated with size at stocking for lake sturgeon Acipenser fulvescens (Rafinesque 1817) stocked in Black Lake, Michigan, USA

The authors conducted a gillnet survey in 2013 in Black Lake, Michigan, USA to evaluate the lake sturgeon (Acipenser fulvescens) stocking programme that began in 2001. Objectives were to (i) estimate year-class specific abundance of juvenile lake sturgeon in Black Lake; and (ii) determine year-class specific survival of stocked year classes and determine whether year-class-specific first-year survival was related to average size at the time of stocking. Deployed were 15 and 20cm stretch mesh gillnets at 72 randomly selected sites in Black Lake over a 3-week survey using a Schnabel multiple-mark, multiple-recapture estimator to determine overall abundance of stocked fish. Ages for captured fish were determined from fin ray cross sections and the presence of coded wire tags, and apportioned the overall abundance estimate of juveniles to year class using an age-length key. Overall survival estimates were calculated by dividing the year-class specific abundance estimates by the number of fish stocked that year. Also evaluated was the relationship between first-year survival and average total length (TL) at time of stocking using logistic regression. Overall survival from stocking to 2013 ranged from 0.03 to 0.53. First-year survival was positively associated with average TL at stocking, and ranged from 0.05 for fish stocked at 9cm TL to 0.84 for fish stocked at 22cm TL. Estimation of future cohort-specific abundance based on size-based expected survival allows managers to establish annual stocking targets that should lead to the achievement of long-term population goals for adult abundance.