Effects of Variable Prey and Cohort Dynamics on Growth of Young-of-the-Year Estuarine Bluefish: Evidence for Interactions between Spring- and Summer-Spawned Cohorts

Abstract

Previous field studies of bluefish Pomatomus saltatrix have documented variation in young-of-the-year (age-0) growth rates among years and between spring- and summer-spawned cohorts. However, the potential factors responsible for generating variable growth in age-0 bluefish have not been investigated. We constructed an individual-based model that combined size-dependent bluefish foraging with a bioenergetics model to quantify the potential effects of variable prey fish dynamics on first-summer growth of juvenile bluefish. We used long-term monitoring data to define baseline conditions and calibrate the model. We then performed three simulation experiments designed to assess the effects of initial density and arrival timing of prey species and bluefish cohorts on bluefish length distributions on October 1. Simulation experiments indicated that spring-spawned bluefish were robust to fluctuations in prey dynamics because of a spawning strategy that ensures temporal overlap with a diversity of prey fish species. In contrast, summer-spawned bluefish were sensitive to variation in prey fish dynamics because of their dependence on a single prey species. Model results also revealed the potential for the time of arrival and the initial density of the spring-spawned cohort to affect the growth of the summer-spawned cohort. Our findings demonstrate that population-level interactions between bluefish and their prey can be complex and have a considerable influence on the early growth rates of the summer-spawned cohort.