ABSTRACT Objective The goal of this study was to characterize the variability in age, growth, and life history of sea-run fish throughout a large, East Coast, USA, watershed to improve the parameterization of longitudinal variation in demographics and spawning histories in an undammed river. Methods Both live and dead American Shad Alosa sapidissima were collected during spring 2020 and 2021. Sex, length, age, and repeat spawning information were recorded for all individuals (n = 512). Growth curves were created to test hypotheses about the variables that were related to the growth rates of American Shad for this relatively unsampled portion of the spawning population in the Delaware River. Results We observed variation in size, age, repeat spawning probability and propensity, and sex ratios from downstream to upstream as well as during the spawning season. Individual traits also varied among the fish that died during migration and those that were collected alive. Conclusions This study expands the current knowledge about variability in the life history traits that are commonly used in assessing and managing an anadromous fish that spawns upstream in a large, undammed watershed. Our results have broad implications for the assessment and management of anadromous fish populations globally and contribute to understanding parity along a continuum. Some potential priorities for future work include using telemetry to understand the final disposition of live fish, investigating fine-scale genetic control for correlated life-history traits, and investigating the correlations between natal origin (i.e., genetic stock mixing) and longitudinal variation within spawning populations.
Best et al. (2026) studied this question.