YOU ARE WHAT YOU EAT??
What do herring eat?Herring survive entirely by feeding on plankton - the tiny drifters of the ocean. There are two basic types of plankton: phytoplankton (plants) and zooplankton (animals). The zooplankton community, comprised of invertebrate and fish larvae as well as many species that remain drifters for life (holoplankton), is thought by some scientists to be the biggest source of protein in the world's oceans and is, not surprisingly, an important food source for many organisms. Although herring are opportunistic feeders, they feed primarily on small holoplanktonic crustaceans called copepods
Copepods and other tiny crustaceans are the predominant members of the zooplankton in the coastal waters of the Gulf of Maine.  Two copepod species, Pseudocalanus minitus and Calanus finmarchicus comprise more than two thirds of the herring's diet in winter through summer, with three other copepod species the dominant food sources in the fall. The larvae (nauplii) of copepods make up a major part of the diet of larval herring.
The survival and distribution of herring in the Gulf of Maine depends largely on the distributions their major prey, the copepods. Herring growth rates vary with copepod availability and abundance. The copepod Calanus finmarchicus, perhaps the most abundant copepod in the Gulf of Maine, is vital to the success of Atlantic herring populations. Atlantic herring time their migrations around the presence of this copepod. The herring are dependent on these food sources to such a degree that herring scientists have proposed that information on prey species may provide a method to predict the location of herring stocks.
Herring feed at night in the upper water column, following the massive vertical migrations of zooplankton that inhabit deep waters by day and surface waters by night. Research has shown that herring feed on zooplankton in several ways. Much like the way a whale strains zooplankton from the water with its baleen plates, herring are able to use their gill rakers to filter-feed. Herring can also visually detect larger prey, such as an individual copepod or a mysid shrimp, and execute directed attacks on these targets
Funded by the Maine Sardine Council, the National Fish and Wildlife Foundation, and Stinson Seafood, Inc.