The Gulf of Maine Research Institute has quite a bit of good information about herring posted on-line.
Did you know: "The herring is a fish of open waters, traveling as a rule in schools of hundreds or
thousands; single fish are seldom seen, or even small companies of a few dozen.
As a rule all the individual members of a school are about the same size,
whether large or small. It is not known how long any given school may preserve
its identity as such."
Read this article to learn more:
Many thanks to the Gulf of Maine Research Institute!!!
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