Latent effects of early life history on partial migration for an estuarine-dependent fish

Partial migration is the divergence of a population into migratory and resident contingents. This behavior is well documented for many diadromous species, but proximate causes of partial migration in fishes are poorly understood. Here, we tested the hypothesis that migratory and resident contingents within a population of white perch (Morone americana) are associated with larval growth and mortality rates, where slower growth and higher mortality was associated with migratory behavior. In addition, we examined the influence of environmental factors (temperature, zooplankton density, and freshwater flow) on larval vital rates. In 2005, an intensive field survey was conducted in the Patuxent River estuary (Chesapeake Bay, MD). Otolith microstructure analysis was used to determine vital rates of larvae and back-calculate hatch-date distributions of juveniles from resident and migratory contingents. Migratory contingent fish originated primarily from early-spawned larval cohorts, which were characterized by slower growth compared to later spawned cohorts. In contrast, resident juveniles tended to originate from later-spawned cohorts with faster growth. Zooplankton densities supported the inference that favorable larval growth conditions occurred later in the larval production period. The results support latent effects on partial migration of white perch related to spawning phenology, its interaction with temperature, and resultant larval growth rates.