Depth selectivity and spatial distribution of juvenile lake sturgeon in a large, fragmented river

Lake sturgeon are considered imperilled across much of their range where rehabilitation efforts have been employed to enhance recovery. Habitat requirements are not known for all life stages of lake sturgeon, especially the juvenile stage. Juvenile lake sturgeon can be important in assessing effectiveness of rehabilitation efforts and therefore life history requirements for this stage is important. The objectives of this study were to determine if juvenile lake sturgeon within the Ottawa River, Canada has a depth preference; if so, to determine if depth selectivity was a function of body length; and finally, to determine if spatial structuring exists for juvenile lake sturgeon within reach type (i.e. impounded vs unimpounded reaches). A depth stratified, index netting program selective to juvenile lake sturgeon was conducted in the Ottawa River, Canada from 20082010. Overall, a total of 192 juvenile lake sturgeon were sampled. A Bayesian approach was used to analyze the data including logistic regression, Poisson regression and generalized linear model. The probability of capturing a juvenile lake sturgeon in a net and their relative abundance was greatest as the 1220 m depth stratum and lowest at 3550 m depth stratum in both impounded and unimpounded river reaches. Lake sturgeon mean total length was smallest at shallowest depth stratum (13 m) and greatest in the deepest depth stratum (5075 m). For spatial segregation, mean total length of lake sturgeon was significantly smaller in the lower reach of the three contiguous, unimpounded reaches whereas the trend was opposite in impounded reaches where the smallest lake sturgeon were sampled in the upper third of the river reach. This study therefore identified areas where the probability of capturing a juvenile lake sturgeon is the greatest and where to best expend efforts through a stratified random sample study design when conducting effectiveness monitoring of any restoration or management actions.