Interannual variability in size-selective winter mortality of young-of-the-year striped bass

Early life stages of fish are characterized by high size-selective mortality rates, with selection generally acting against smaller, slow-growing individuals. Here, we investigate, for the St. Lawrence River striped bass (Morone saxatilis) population, how size of young-of-the-year juveniles (YOYs) affected survival from the pre-wintering period until the following spring, by comparing their otolith daily growth trajectory to that of one-year-old juveniles (OYOs). Otolith growth in the first 50 d after hatch was faster in post- than in pre-winter juveniles in both years, indicating that fast-growing individuals were more likely to survive to the next spring. A larger back-calculated size at age 1 in the 2016 year class compared to that observed in 2017 also suggests interannual variability in size-selective overwinter survival. Our results indicate that the design of YOY abundance surveys aimed at predicting annual recruitment strength needs to account for the effect of size-dependent mortality until the end of the first winter of life, as high abundance of relatively small YOYs in autumn may not necessarily translate into a large number of OYOs in the following spring and thus into high recruitment.