Effects of Biotic and Abiotic Factors on Growth and Relative Survival of Young American Shad, <i>Alosa sapidissima</i>, in the Connecticut River

Abstract

We examined the hypothesis that temporal oscillations in zooplankton abundance, river flows, and temperatures in the Connecticut River affect the survival and growth rates of larval and juvenile American shad, Alosa sapidissima, among 5-d cohorts. The relative survival rates between newly hatched shad larvae and juveniles were low among early cohorts (May 21 – June 15), but rose rapidly among later cohorts (June 21 – July 6) when river flows were low and temperatures and zooplankton densities were high. Age of larval and juvenile shad was estimated by counting daily rings on sagittal otoliths and age-specific length increments determined by backcalculation techniques. Cohort-specific growth rates of larval shad increased linearly with rising zooplankton densities, and asymptotically with rising river temperatures and declining flows. By contrast, juvenile growth rates among 5-d cohorts showed no significant linear or nonlinear relationships to water temperatures and flows.