Size-structured piscivory:advection and the linkage between predator and prey recruitment in young-of-the-year bluefish

The interaction of size-structured predator and prey populat~ons can affect the recruitment success of both predators and prey.Here, we examine how the timing and location of spawning, advective processes, and size-structured predator-prey interactions may influence the ecology and life history of an offshore-spawning, estuarine-dependent marine fish.Bluefish Pomatomus saltalrixrecruit to mid-Atlantic Bight estuaries as 2 distinct cohorts.The predominant spring-spawned cohort results from: (1) spawning in the South Atlantic Bight in March and April, (2) advection northward along the edges of the Gulf Stream, and (3) an active migration into New York/New Jersey (USA) estuaries in June and July.A second less abundant cohort resulting from summer-spawning in the mid-Atlantic Bight recruits to inshore areas in August.This inshore recruitment entails a dramatlc habitat shift that coincides with a feeding shift from planktivory to piscivory and a large increase in growth rates.We hypothesized that the migration of spring-spawned young-of-the-year (YOY) bluefish into northern estuaries at an advanced s u e facilitates piscivory on the local inshore fishes that become their principal prey.We tested this hypothesis by determining the annual recruitment date of YOY bluefish and their prey, and by examining the diet and prey slze selectivities, and predator size-prey size relationships of YOY bluefish in Great South Bay (GSB), New York.Our results showed that: (1) the date of juvenile recruitment into GSB coincides with the appearance of their main prey item, Atlantic silversides Menidia menidia; (2) YOY bluefish feed primarily on the most abundant prey available in GSB; and(3) bluefish are size-selective, consistently ingesting small prey sizes.These results suggest that advection into high latitudes permits spring-spawned bluefish to exploit habitats at an earlier time and at a larger size than would otherwise be possible.This unique strategy also allows bluefish to accelerate the onset of piscivory by timing their estuarine entry with the appearance of small coastal fishes.The relationships between bluefish and their prey are determined by a complex interplay between recruitment timing of both predator and prey, relative prey (size and type) abundances and predator selectivities.The observed pattern of spawning, advection and recruitment to nursery areas, which is common to other bluefish populations, may represent a reproductive strategy that maximizes growth and survival.