Age structure and seasonal movement of Atlantic sturgeon (Acipenser oxyrinchus) aggregating in eastern Long Island Sound and the Connecticut River

Atlantic sturgeon (Acipenser oxyrinchus) seasonally aggregate in Long Island Sound and the Connecticut River, but their size and age structure and use of the river remain insufficiently understood. We analyzed all available length data from monitoring efforts (1988–2021: number of samples [n]=3544), estimated age from sections of pectoral-fin spines (n=296), and measured annuli widths for retrospective size-at-age analysis (n=166). Fish ranged from 21 to 218 cm in total length ([TL], mean: 105.2 cm TL), but 87% of them measured 50–130 cm TL. Ages ranged from 0 to 18 years (mean: 8.1 years), with 92% of all individuals estimated to be younger than 12 years. Annuli widths indicate that faster growing fish selectively disappeared from the study area over time. To reveal movement patterns, particularly for the upper Connecticut River (freshwater), we analyzed 3 years (2019–2021) of acoustic detections of 85 individuals. These fish occurred in the study area from March through November but stayed on average only 54–91 d. The majority of fish entering the receiver arrays in Long Island Sound also moved into the river but largely utilized its lower, brackish estuary. Still, a large proportion of individuals (35%–66%) made upriver excursions into freshwater, and the timing coincided with low flow and warm river temperatures in late summer. Therefore, both the brackish and freshwater portions of the Connecticut River serve as important seasonal feeding habitats for Atlantic sturgeon ≤130 cm TL.