Fall and winter estuarine recruitment of bluefish Pomatomus saltatrix: selectivity for large lipid-rich prey increases depleted energy levels

The early life history of bluefish Pomatomus saltatrix follows a complex cycle with several migrations to and from estuarine nurseries. In contrast to spring and summer, little is known about fall and winter estuarine habitat use of juvenile bluefish. Here, we examined fall and winter estuarine ecology of juvenile bluefish in the Matanzas River Estuary in northeastern Florida over a 2 year period. Three distinct intra-annual cohorts of young-of-the-year (YOY), and age 1+ fish were identified through size frequencies and verified with otoliths. Estuarine recruitment was first observed in late October by spring-spawned and age 1+ fish, followed by summerspawned YOY, and finally by the fall-spawned cohort with no new recruitment after February. Interannual differences in the timing of estuarine entry were likely due to variation in shelf cooling. A peak in relative abundance was observed in December. The highest relative abundances were found near the sandy inlets. Fish dominated the diet of all bluefish cohorts, mugilids by age 1+ and spring-spawned YOY bluefish, and engraulids by summerand fall-spawned YOY. In contrast to previous studies, YOY and age 1+ bluefish were strongly selective for Mugil spp. prey. Bluefish lipid content increased over the fall and winter, peaking in January. A comparison of prey lipid levels across 30 potential prey species showed that Mugil spp. had the highest lipid content, 5 to 6× higher than lipid levels in other common prey items. We conclude that juvenile bluefish use Florida estuaries during the fall and winter to increase depleted lipids through selective feeding. Year class strength and cohort survival may be strongly related to the availability of selected prey items during this time.