Age, Growth and Genetic Markers of Semelparous vs. Iteroparous American Shad (Alosa sapidissima) in the Upper Delaware River 2020-2021

Abstract

The goal of this study was to characterize variability in age, growth and life history of American shad (Alosa sapidissima) throughout the upper Delaware River. Both live and dead American shad were collected during spring 2020 and 2021. Sex, length, age, and repeat spawning information were recorded for each individual (n = 512), in addition to whether they were collected alive or dead. Several von Bertalanffy growth curves (VBGF) were created to both test hypotheses about variables affecting the growth rates of American shad, as well as to produce accurate growth estimates for this relatively unsampled portion of the spawning population in the Delaware River. Spawning American shad collected from the upper Delaware River were 6 years old on average. About half (48%) of the fish collected possessed repeat spawning marks. Average fork length decreased and average age increased with distance sampled upstream. A sex-based model was determined to be the best predictor of growth and was combined with the river mile of capture and young-of-year length data to estimate population parameters. The results of this study expanded knowledge about several life history characteristics of spawning American shad in the upper reaches of the Delaware River and can be used by fisheries managers during stock assessment to better predict growth rates and the mortality of American shad spawning in this geographic location.