Pre-Migration Patterns of Growth, Energy Dynamics, and Resource Use in Multiple Cohorts of Juvenile Bluefish in the Hudson River Estuary, New York

In fish populations, interactions between age-classes may be an important source of density dependent population structuring, especially if there is a disparity in competitive ability among the cohorts.  Inter-cohort competitive interactions within a single year class have rarely been investigated and may have implications for recruitment success.  Our objectives were to examine the interaction between cohorts of juvenile bluefish (Pomatomus saltatrix) prior to the autumn migration in the Hudson River estuary, 2008/2009, and assess the potential effect of the interaction on recruitment dynamics by comparing growth and lipid content.  Hatch-date analysis corroborated the presence of spring- and summer-spawned cohorts.  Diet overlap was high while spatial overlap was low between the 2 cohorts throughout the summer and early autumn.  Growth was similar between the cohorts, and white muscle lipid content was higher in the summer cohort than in the spring cohort.  Lipid levels increased in the summer cohort and declined in the spring cohort until September, but declined in both cohorts after September.  Our results indicated that differential habitat use between the cohorts was not associated with a foraging cost for the smaller summer cohort as cohort-specific growth rates were similar, and lipid content was higher in the summer cohort.